The Science of Ice Cream Meltdown and Structural Collapse: A Comprehensive Review

ABSTRACT

Ice cream exhibits distinct meltdown behaviors at room temperature, as determined by the structural aspects created during manufacturing. In general, as the ice melts, ice cream either turns completely into a flowing liquid (complete collapse) or retains a portion of its original shape (partial collapse), leaving a solid‐like melted ice cream foam. Melting tests enable researchers to compare structural changes in ice cream under controlled conditions, providing insight into how formulations and processing parameters influence ice cream stability. The microstructure formed during production significantly impacts meltdown behavior, affecting both the melting/collapse rate and the ability to retain shape. Key factors such as fat destabilization, overrun, mix viscosity, and serum phase properties all play crucial roles in determining melting characteristics. For instance, higher fat destabilization can form a fat network that stabilizes air bubbles and resists foam collapse, while increased overrun reportedly slows melting due to the insulating effect of air cells. Mix viscosity and serum phase properties also influence the flow properties of the melted ice cream. This review discusses the influence of these structural components on meltdown behavior, providing a comprehensive understanding of the interplay between formulation, processing, and microstructure. Furthermore, the rheology helps explain the fundamental mechanisms of ice cream melting and collapse, aiming to inform the development of ice cream products with desirable melt‐resistant properties.

1. Introduction

The meltdown behavior of ice cream is an important quality attribute that directly impacts the consumer taste experience. It reflects the structural stability of the product under ambient conditions, which is critical for ensuring both consumer satisfaction and consistent product performance. Rapid melting of ice cream may lead to undesirable dripping and loss of its intended shape, typically resulting in a dome‐shaped meltdown, as shown in Figure 1. On the other hand, excessively slow melting may not be ideal for soft serve ice cream, which benefits from a dome‐shaped meltdown behavior. Beyond consumer preference, meltdown behavior is also an important factor in the industry for evaluating product stability, particularly for frozen novelties such as ice cream sandwiches and ice cream bars, which need to maintain their designed shape during potential extreme temperature fluctuations in cold‐chain distribution and storage conditions, with possible melt–refreeze processes involved. Understanding meltdown behavior is essential for manufacturers seeking to optimize formulations and processing conditions. The rate and pattern of melting are influenced by multiple factors, including ingredient composition, processing parameters, and storage conditions. As a result, measuring and characterizing meltdown behavior is critical for ensuring product consistency, quality control, and shelf‐life stability.

FIGURE 1.

The typical meltdown curve, shape retention during melting, and structural change illustration for two types of meltdown behaviors, completely drip‐through (left) and melted ice cream with remnant foam (right). The curves of completely drip‐through samples typically do not reach to 100% of the drip‐through portion due to water evaporation and residual foam left on the mesh. Figure was adapted from Wu (2023).

Ice cream meltdown behavior is intricately linked to its internal structure. Ice cream represents a complex system composed of three primary phases: air, solid, and liquid (Goff and Hartel 2013). Air, manifesting as air bubbles, is introduced during the freezing process, where it is incorporated by either whipping or injection as part of the water‐to‐ice transition. At freezing temperatures, solids are present as crystallized milk fat and ice crystals. Milk fat typically exists in two forms: individual fat globules and fat clusters, with the latter known to slow the melting process. The liquid component of ice cream consists of the concentrated unfrozen serum phase that develops during freezing, with solutes like stabilizers, emulsifiers, sweeteners, and salts concentrated in this phase, while most of the water transitions into ice (Goff 1997a). These constituents interact throughout the ice cream production process, collectively influencing the ultimate microstructure of the ice cream and, in turn, its meltdown characteristics.

The meltdown test is one of the oldest and most common methods employed by researchers and scientists to characterize ice cream melting properties with varying formulations and processing conditions. Dating back to 1916, one of the earliest meltdown tests was conducted by Holdaway and Reynolds (1916). Since then, researchers and scientists from industry and academia have widely adopted this test for quantitatively measuring the melting process of ice cream and further innovating and reformulating ice cream. The ice cream meltdown test has evolved over the years, transitioning from the practice of placing a brick of ice cream on a wooden board and measuring the weight of the melted ice cream over a specific time interval, as done by Holdaway and Reynolds (1916). Modern practices involve taking a slice of ice cream, either with the same weight or the same volume, directly from the freezer and placing it on a wire mesh. Below the mesh, a scale records the melted ice cream as it drips through, often referred to as the “drip‐through” part, at regular time intervals. The weight of the melted ice cream that passes through the mesh is then plotted over time to construct the meltdown curve, typically exhibiting a sigmoid shape. Depending on the specific structure of ice cream, the duration of a complete meltdown test can vary, resulting in variations within the meltdown curve and the parameters obtained (Alvi and Martinez‐Monteagudo 2023).

The terms “meltdown test” or “drip‐through test” are often used interchangeably in the literature, although the processes they measure are not identical. Specifically, dripping is not always equivalent to melting. In some cases, the ice in ice cream will melt but product retains its shape on the mesh due to the structural stability, which slows or delays the dripping process. As a result, the curve generated by this test reflects the melted ice cream “drip‐through” process rather than the ice crystal melting process. Since it is challenging to measure the melting process in real time, the drip‐through curve is often used as a proxy to describe the melting process. Here, the term meltdown test is used in accordance with common usage in the field, while clarifying its practical limitations in capturing the actual melting process.

A complete meltdown curve in a sigmoid shape is characterized by three phases: the lag phase, the fast‐melting phase, and the stationary phase, corresponding to three parameters: induction time, melting rate, and the amount of melted ice cream left on the mesh at the end of the meltdown test (Wu et al. 2019), as shown in Figure 1. During the initial lag phase, which marks the period before the first melted ice cream drip, heat penetrates the ice cream, initiating the melting of ice crystals from the outside toward the interior. As heat penetrates the ice cream, some is absorbed as latent heat for ice melting, which reduces the rate of temperature increase attributable to thermal diffusivity. The melting of ice dilutes the serum phase, reducing its viscosity and increasing its fluidity, eventually leading to the onset of the second phase, known as the fast‐melting phase. During this stage, the melted ice cream begins to flow through the wire mesh, primarily driven by the force of gravity, until it reaches its maximum meltdown rate, which is calculated from the slope of the linear section of the curve (Koxholt et al. 2001). Within the fast‐melting phase, the rate and extent of ice cream collapse are dependent on the presence of remaining structural components, including air cells and clusters or globules of fat. When numerous fat clusters are situated around the air cells, they can jam together as the mass begins to collapse and block the lamella between air cells, impeding the flow as the serum begins to drains, thus forming a three‐dimensional network with the air cells. This network formation results in a gradual slowdown of the meltdown process, which more precisely reflects a reduction in the rate of structural collapse, as by that stage all ice crystals have already melted and no further phase change occurs. This ultimately marks the transition to a steady state, characterized by minimal weight change in the melted ice cream. In some cases, slow‐melting ice creams may require 4–8 h to reach this steady state. In cases where only a few fat clusters are present, the ice cream melts from the outer layer to the inside in a hemispherical shape, layer by layer, until the entire ice cream sample has fully passed through the mesh without leaving any melted foam behind. At some point, the meltdown process ultimately transitions into the stationary phase without further drainage.

Simultaneously, a range of meltdown parameters, beyond the melting rate, has been derived from this test. These parameters include the shape factor (Cottrell et al. 1979), the half‐life for melting of the ice cream (referring to the time it takes for half of the original ice cream mass to drip through the mesh) (Roland et al. 1999), the induction/lag time when the first melted ice cream dripped through (Rathnakumar et al. 2023), the percentage of remnant foam left by the end of the melt test (Liu et al. 2022), and the diameter and height measurement of the melted ice cream (Alvarez et al. 2005). Additionally, predictive models have been developed to describe the meltdown curve (Alvi and Martinez‐Monteagudo 2024). The aim of quantifying these diverse parameters obtained from the meltdown test is to establish connections between ice cream microstructure and its meltdown behavior, offering insights into variations in ice cream quality and stability when exposed to temperature fluctuations.

This review seeks to offer a comprehensive overview of ice cream meltdown, encompassing the processes of ice melting and structural collapse. It also explores the influence of ingredients and process conditions on meltdown, along with examining the correlation between rheological parameters and the melting process. Since ice cream is a complex system with multiple structural components influencing the overall behavior, it is important to note that changes in one parameter or ingredient often affect other structural aspects (Masuda et al. 2024; Gallagher and Hartel 2025; Gao et al. 2025). This can make it difficult to isolate the effect of a single factor on melting. This complexity likely contributes to the inconsistent results observed in the literature. Therefore, while the structure is discussed in detail below, it is essential to remember that no single factor completely governs the melting process by itself and that melting is the result of complex interactions among the structural aspects.

2. Ice Cream Structures and Effects on Meltdown

The structure of ice cream plays a crucial role in its meltdown behavior. Although the rate at which ice cream melts may not necessarily correlate with sensory attributes or other attributes of product quality, altering the structure of ice cream through formulation or processing adjustments can achieve desired melting characteristics in terms of melting rate and shape retention (Figure 2). For instance, structural modifications can result in a visually appealing hemispherical meltdown for soft serve or improve shape retention during storage and distribution. This section will explore the key structural components of ice cream and their impact on meltdown behavior, highlighting how structural adjustments can influence the final product performance. While the influence of each structural component on meltdown behavior is discussed, isolating individual components in practical applications is challenging, as they work together to form the ice cream microstructure and determine its melting properties.

FIGURE 2.

The shape retention of ice cream with various microstructural elements, including overrun, mix viscosity, and fat destabilization, and its illustrations. Figure was adapted from Wu (2023).

2.1. Fat Structure

The fat in ice cream, particularly milk fat, provides a rich and creamy flavor, a smooth texture during consumption, and structural stability during temperature fluctuations. Common milk fat sources include fresh cream, unsalted butter, and anhydrous milk fat, with nondairy options including coconut oil, palm kernel oil, and sunflower oil. Beyond its sensory contributions, the structure of fat is crucial in determining the meltdown behavior of ice cream. Key parameters, such as the size and distribution of fat globules and the formation and extent of fat cluster formation (fat destabilization), significantly influence resistance to melting and structural collapse. These structural attributes are shaped by both composition and process parameters, including the type of emulsifiers used, the solid fat content (SFC), the viscosity of the ice cream mix, and processing conditions such as homogenization and freezing. Even freezing point depression influences fat globule destabilization by affecting ice crystallization, which, together with the shear forces generated during freezing, drives the extent of destabilization (Goff and Jordan 1989).

After the homogenization process, larger fat globules have been broken down into smaller ones in a narrower size distribution. This reduction in particle size limits the tendency of fat globules to separate. Additionally, proteins adsorb onto the surface of these smaller globules, contributing to their stability and preventing coalescence. Fat destabilization occurs during the freezing process, where the presence of low‐molecular‐weight surfactants (LMWSs), commonly known as emulsifiers, can enhance the extent of this destabilization. Emulsifiers are highly effective at reducing the interfacial tension between the serum phase and fat globules at low temperatures, surpassing the performance of casein. This reduction in interfacial tension and net free energy allows emulsifiers to displace proteins through the orogenic effect, thereby decreasing protein adsorption to the fat globule surface and increasing its presence in the serum phase during the aging step (Dickinson and Gelin 1992; Dickinson et al. 1999; Wilde et al. 2004; Maldonado‐Valderrama et al. 2007, Maldonado‐Valderrama et al. 2008; VanWees et al. 2022). As a result, the fat globule surface retains more LMWSs, leaving it more susceptible to rupture during shearing than a protein interface. Consequently, fat globules coated with more emulsifiers and fewer caseins are less stable when exposed to shear forces during freezing (Fredrick et al. 2010). In the freezing stage, the presence of emulsifiers and solid fat within the globules contributes to their rigidity and prevents complete coalescence. This destabilization leads to the clustering of individual fat globules, forming large (∼100 µm) fat aggregates (Thiel et al. 2016). Fat destabilization is crucial in frozen desserts, as it enhances dryness during extrusion and packaging, ensures a smooth texture, and improves resistance to melting by reducing the melting rate and promoting better shape retention throughout the meltdown test.

During freezing and aeration, fat globules and clusters either migrate to the air cell surface, serving to stabilize air bubbles by hindering coalescence between adjacent air cells, or remain within the unfrozen serum phase (Goff, Verespej, et al. 1999; Liu et al. 2022). The formation of large fat aggregates resulting from fat destabilization plays a crucial role in slowing the melt rate and reducing structural collapse during the melting process. During meltdown, the transition from ice crystals to water causes a dilution of the unfrozen phase, reducing viscosity and increasing fluid mobility, which causes the melted liquid to flow and drain. When a sufficient quantity of large fat aggregates is present in the lamella and the thickness of lamella is smaller than the size of these fat aggregates, the destabilized fat aggregates undergo restructuring as the system begins to collapse. These fat globule clusters jam together and effectively block the lamella, forming a fat network that slows the drainage of the liquid phase and stabilizes the air cells, which is essential for maintaining ice cream foam stability, even as it melts (Koxholt et al. 2001). Ultimately, one of the crucial factors that determine the amount of melted ice cream foam matrix that remains at the end of the drip‐through test is the strength and stability of the fat network, as depicted schematically in Figure 2.

Manipulating factors such as fat type and quantity, the type and concentration of emulsifiers and proteins, ice cream mix viscosity, and processing conditions (especially during homogenization and freezing) can significantly affect fat globule size and destabilization. These changes have a substantial impact on the formation of the fat network within the ice cream, leading to a wide range of meltdown behaviors observed in meltdown tests, including melting rate and structural collapse behavior.

Solid fat content (SFC), or the amount of crystalline fat contained within each fat globule, affects the meltdown rate mainly by influencing the degree of fat destabilization. Partial coalescence of fat can only occur if the fat globules have the proper SFC. When SFC in the mix is too low, complete coalescence among fat droplets takes place, whereas with higher SFC, the fat network within each droplet becomes excessively rigid, hindering coalescence and maintaining droplet separation (Pawar et al. 2011; Thiel et al. 2016). Neither fully coalesced nor rigid fat droplets can form the desired fat network needed to slow the melt rate and preserve the structural integrity of the melted ice cream. Different degrees of SFC in the ice cream mix can be achieved by altering the ratio between saturated and unsaturated milkfat fractions (Méndez‐Velasco and Goff 2012), the degree of saturation of emulsifiers (Barford et al. 1991), and aging temperature and time (Abd El‐Rahman et al. 1997; Zhao et al. 2023).

Commercially, an easy and a more common approach to changing SFC is to blend different fat sources, such as combining milk fat and vegetable oil or adding various plant‐based fats, to achieve the desired SFC in the mix for partial coalescence. For example, an SFC of 60%–80%, which can be achieved by blending liquid and solid fats from palm kernel oil and high‐oleic sunflower oil, results in a high degree of fat destabilization and a slow melting rate, whereas SFC values outside this range lead to a faster melting rate (Sung and Goff 2010). Similarly, a blend of coconut oil and milk fat with an SFC range of 55%–68% produces more fat aggregates compared to ice cream made with only milk fat (Liu et al. 2022). The higher SFC enhances particle interactions, leading to stronger fat aggregation and a longer induction time before the ice cream starts to drip. Regardless of the fat source or method of adjustment, the key factor is that the elastic energy, the energy resisting coalescence due to the internal fat structure, must reach a sufficient threshold to allow deformation of the fat network as globules change shape during coalescence (Thiel et al. 2016). Thus, the ideal SFC range for any fat source or combination of fats cannot be determined beforehand and requires preliminary trials to identify the optimal conditions.

In addition to fat composition, emulsifiers play a significant role in modifying the crystallization behavior of fat, influenced by their varying chain lengths and degree of saturation (Munk et al. 2013; Jiang et al. 2019). Lipophilic emulsifiers, such as mono‐ and diglycerides and lactic acid ester of mono‐diglycerides (LACTEM), exhibit a structure similar to triacylglycerols in the oil phase, enhancing interfacial heterogeneous nucleation through a template effect (Sakamoto et al. 2004; Jiang et al. 2019). In contrast, hydrophilic emulsifiers, such as polysorbate 80, excel at reducing surface tension between the water and oil phases while remaining in the liquid at the oil–water (O/W) interface, promoting partial coalescence and further reducing the melting rate. Both types of emulsifiers effectively lower interfacial tension, which supports efficient protein displacement (Thiel et al. 2016; Goibier et al. 2017; Wang et al. 2021).

Proteins in ice cream not only contribute to its nutritional value but also play a key role in stabilizing the air–water (A/W) and oil‐water (O/W) interfaces, thereby influencing fat destabilization. The thickness of protein coverage on the O/W interface, the ability of the proteins to reduce interfacial tension, and the extent of surface coverage all play crucial roles in determining the degree of partial coalescence under the influence of shear forces during freezing. In the realm of dairy ice cream, whey protein and casein are the primary proteins influencing fat stabilization. Specifically, casein demonstrates superior efficacy in stabilizing fat compared to whey protein (Goff et al. 1989; Goff 1997b). Globular serum proteins, such as whey protein, form a thick and elastic layer around fat globules but are more easily disrupted by shear forces and more prone to fat destabilization than casein‐stabilized emulsions. In contrast, casein forms a cohesive protein film that creates a strong steric barrier at the interface, making it more resistant to emulsifiers attempting to reduce surface tension (Pelan et al. 1997; VanWees et al. 2022; VanWees 2024). Generally, the degree of fat destabilization decreases with an increase in protein content due to the formation of a thicker adsorbed protein layer at the fat globule surface and a higher surface coverage area. This increased coverage makes it more difficult for LMWSs to displace proteins (Segall and Goff 1999). Notably, ice cream containing 10% protein forms an exceptionally stable emulsion, with no observed fat destabilization (Segall and Goff 1999; Alvarez et al. 2005; Daw and Hartel 2015).

Adjusting the protein ratio or concentration can influence fat destabilization in ice cream, whereas a novel processing method controls protein adsorption on fat droplets by limiting the type and amount of protein available during homogenization. In the 1970s, Mussellwhite and Walker (1971) proposed a new method to control protein adsorption to fat, promoting fat destabilization without the need for emulsifiers. This process involved separating ingredient streams during homogenization and pasteurization, which were then re‐combined before freezing. One stream contained all the fat, a small amount of protein, and water, while the other stream included the remaining ingredients (with no emulsifiers). This approach resulted in a stable emulsion during aging, which underwent partial coalescence under shear forces in the freezer barrel without the requirement of emulsifiers (Segall and Goff 2002a, 2002b). Although not widely used in the industry, controlling protein adsorption during production could provide valuable insights for future clean label innovations in the ice cream industry.

Shear forces are critical in shaping the microstructure of ice cream, particularly during dynamic freezing, where they influence both fat destabilization and air incorporation. While homogenization reduces fat droplet size, it is during dynamic freezing that shear forces generated by the rotating dasher promote partial coalescence of fat globules. This process contributes to the formation of a fat network that stabilizes air cells and impacts the meltdown behavior of ice cream. The formation of ice crystals increases the viscosity of the ice cream slurry, altering flow behavior and intensifying the mechanical interactions from the dasher. This, in turn, promotes collisions between fat globules and facilitates partial coalescence. While shear forces originate from the mechanical action of the dasher, their impact on the ice cream mix and final frozen product is modulated by formulation factors like viscosity, total solids, and ice phase volume, along with processing parameters such as freezer design and dasher speed.

The viscosity inside the barrel depends on ice cream ingredients, such as hydrocolloids, and the temperature, which governs both the serum phase viscosity and the extent of ice crystallization. Higher viscosity generally enhances fat destabilization by generating greater shear force in the scraped surface freezer barrel. Adding stabilizers at concentrations up to 0.4% significantly promotes fat destabilization, even without the use of polysorbate 80 (Wu et al. 2019). Greater fat destabilization typically occurs in continuous freezers, as the continuous flow and higher shear rates enhance the frequency of fat globule collisions compared to the more static, intermittent churning conditions in batch freezers (Goff, Verespej, et al. 1999; Goff and Hartel 2013). Increasing dasher speed also enhances fat destabilization, regardless of the emulsifier combination added to the ice cream (Warren and Hartel 2018). Furthermore, assembling the continuous freezer with increased dasher displacement has been shown to increase fat destabilization due to higher agitation and shear forces, which promotes greater collision among fat globules (Kokubo et al. 1996; Gallagher 2024).

2.2. Air Phase

During dynamic freezing, air is incorporated into the mix through mechanical agitation by the rotating dasher and scraper blades, which disperse air bubbles throughout the partially frozen mix. These air bubbles are stabilized by proteins and emulsifiers adsorbing at the A/W interface, as well as by fat aggregates formed through partial coalescence, which help strengthen and stabilize the air cell structure. The stabilization is further reinforced by increased viscosity in the serum phase and the formation of destabilized fat networks (Euston 2008; Warren and Hartel 2014). Once the ice cream melts, the foam structure begins to break down due to liquid drainage, bubble coalescence, and disproportionation (Foegeding et al. 2006). As a result, the stability and properties of the air bubbles are critical, as they directly influence how well the melted ice cream foam holds up during meltdown.

When a slab of frozen dessert is placed on a screen in a typical meltdown test, heat transfer from the surrounding air (which is at a higher temperature than the frozen dessert) into the product begins immediately. Convection heat transfer occurs at the surface of the frozen product, causing the outside to heat up while the innermost parts remain cold. Heat penetration into the frozen dessert depends on the thermal conductivity of the serum phase and the properties of air phase, namely overrun and, to some extent, air cell size distribution. As heat transfers into the ice cream slab, ice crystals at the exterior begin to melt, absorbing latent heat in the process, as reflected in a decrease in thermal diffusivity (Ben‐Yoseph and Hartel 1998). This results in a reduced temperature increase (compared to a system with no phase change). Furthermore, the drainage and dripping of melted ice cream influence the stability of the melted ice cream foam; greater retention of liquid and fat structure within the foam lamellae reduces the likelihood of two air interfaces merging and rupturing, which would otherwise lead to further collapse of the foam (Wilde and Clark 1996).

Overrun, the air content in frozen desserts, directly impacts the melting process for two reasons. First, the insulating properties of air slow heat penetration during melting. Second, a higher amount of air trapped within the fat network generally enhances the stability of the melted ice cream foam, leading to slower rates of melting and foam collapse and resulting in a greater amount of melted foam remaining at the end of the test (Sakurai et al. 1996; Sofjan and Hartel 2004; Warren and Hartel 2018). This trend is also observed in frozen desserts with overrun levels exceeding 100%. For instance, frozen dessert with 175% overrun had a slower melting rate compared to samples with 100% or 125% overrun (VanWees et al. 2020). Additionally, frozen dessert with 175% overrun retained nearly twice as much melted foam as the 100% overrun samples. This can be attributed not only to the higher number of air bubbles trapped in the melted foam, which helped maintain the structure, but also to changes in other structural elements, such as fat destabilization, which was enhanced by the increased overrun (VanWees et al. 2020). The large volume of small air cells facilitates fat destabilization during production, contributing to the formation of a stronger fat network in the 175% overrun frozen dessert, which further reduces the melting rate (VanWees et al. 2020).

The effect of overrun on meltdown also depends on the type of network, whether it is dominated by ice crystals or fat. In ice cream with fat‐dominated structure, the effect of overrun is limited (Liu et al. 2023b). Ice cream with a thicker serum phase and a stronger fat network shows greater resistance to melting, even with lower overrun. In contrast, well‐stabilized air cells play a key role in the melting process of ice crystal‐dominated ice cream, particularly during the later stages of melting (Liu et al. 2023b). Overall, the effect of overrun on meltdown depends on how well the air is stabilized by the surrounding network, which plays a crucial role in preventing collapse during melting. Although air cell size distribution has been considered a potential factor influencing meltdown behavior, no distinct correlation has been established between air cell size and melting rate, likely because other structural components exert a greater effect or the variation in air cell size is typically too small to detect (Daw and Hartel 2015; Amador et al. 2017; Warren and Hartel 2018).

Changing the type of gas injected or whipped into ice cream not only reduces the need for additives, allowing for a clean‐label premium product without compromising sensory qualities (Bohra 2023), but it also could change melt resistance and melted ice cream foam stability by altering the effectiveness of air incorporation (e.g., changes in overrun under the same processing conditions compared to air), air cell size distribution, or the rate of air bubble growth through reducing disproportionation (Wilde and Clark 1996). Using ultrasound with CO₂ gas bubbles of varying sizes was shown to enhance the melt resistance of soft‐serve ice cream (Adhikari et al. 2020). Samples treated with ultrasound and carbonation showed higher overrun values and slower melting rates compared to control samples without these treatments. The improved melt resistance was attributed to the use of CO₂, a heavier gas than air, which causes the bubbles to rise and collapse more slowly, potentially slowing the melting of carbonated soft‐serve ice cream (Eisner et al. 2005; Adhikari et al. 2020). Similarly, employing supercritical carbon dioxide (SC‐CO₂) for flash freezing also improves the structural properties of ice cream. Longer exposure time (blast time between 1.5 and 2.5 s) to SC‐CO₂ resulted in higher overrun and reduced melting rates (Bohra 2023). These findings highlight that gas selection can be used to tailor microstructural characteristics like overrun, subsequently affecting meltdown behavior.

Pasteurization conditions, particularly combinations of time and pressure, have been shown to influence fat destabilization, air cell size distribution, overrun, and meltdown properties in artisanal ice cream (Lomolino et al. 2023). A short vacuum treatment reduced both the number and size of air bubbles, while extended vacuum application (30 min at 0.05 MPa) significantly increased overrun and produced larger air bubbles compared to non‐vacuum ice cream. This treatment also led to a slower melting rate and a delayed induction time during meltdown tests compared to the non‐vacuum sample prepared at atmospheric pressure. The improvement in melt resistance observed in vacuum‐treated ice cream with higher overrun may attributed to more uniform and smaller fat globules, enhancing surface area for emulsifier displacement and promoting partial coalescence (Dolby 1953; Lomolino et al. 2023). As a result, increased fat destabilization effectively stabilizes air bubbles, contributing to higher overrun and smaller air cell sizes, ultimately leading to a slower melting rate during meltdown test (Wu 2023).

Air bubbles continue to change in size and distribution during storage (Cook and Hartel 2010), which may also affect meltdown behavior. Changes in air cells occur through three main mechanisms: coalescence, disproportionation, and drainage (Chang and Hartel 2002). Storage conditions, such as temperature and storage period, influence the air bubble growth rate through the above mechanisms. Lower storage temperatures slow air cell growth compared to higher storage temperatures. For instance, ice cream stored between −50°C and −70°C showed no significant increase in air cell size, while storage at −18°C for 52 weeks led to a notable increase in size (Park et al. 2015). Regarding the melting rate, ice cream stored at −18°C took longer to melt than samples stored at −50°C and −70°C, while no clear difference was observed for samples stored at −50°C or −70°C. On the other hand, longer storage time enhanced ice cream melt resistance by extending both the first dripping time and total melting time, in proportion to the storage duration over 90 days (Kozłowicz et al. 2019). It is important to note that, in addition to changes in air cells during extended storage or at higher temperatures, other components, such as ice crystal growth and the further concentrated serum phase (due to ice crystal growth), can also contribute to a more melt‐resistant ice cream. Interestingly, frozen desserts with overrun above 100% stored at fluctuating temperatures showed no significant differences in air cell size distribution after 3 weeks with no changes in the meltdown properties (VanWees 2024). This may be attributed to the high degree of fat destabilization, which likely helped stabilize the air cells and maintain steric stability during storage (Barfod 2001; Goff 2002). These findings suggest that dynamic structural changes, together with initial formulation parameters, have a greater influence on meltdown resistance than air cell size alone.

Changes in air cells during storage can also lead to the defect of shrinkage in ice cream, with potentially significant effects on meltdown. Shrinkage occurs when extensive coalescence of air bubbles creates channels in the frozen matrix, reducing air volume and causing the product to collapse, leaving it unable to fill the container (Dubey and White 1996; VanWees et al. 2022). Here, shrinkage refers to the instability and collapse of the air phase when the ice cream foam is in a frozen state, whereas melting is the collapse of unfrozen/melted ice cream foam due to serum flow at or above room temperature. The structural collapse that occurs during shrinkage may alter the microstructure of the ice cream, which in turn affects its meltdown behavior at room temperature. For instance, ice cream made from buffalo milk exhibited shrinkage after 4 weeks of storage at −20°C, coinciding with a notable increase in melting rate (Roy et al. 2021). In contrast, no strong correlations were found between shrinkage and melting properties in high‐protein, high‐overrun frozen desserts (VanWees 2024). This observation may be due to the fact that the collapse of the melted ice cream foam is primarily influenced by the structure of the ice cream matrix and its flow properties rather than the instability of the air cells, which typically cause shrinkage in the frozen structure. Further research is needed to explore the relationship between shrinkage and meltdown properties in ice cream.

2.3. Ice Phase

In a meltdown test, environmental heat melts the ice crystals in the ice cream, removing latent heat. The resulting water mixes with the concentrated serum phase, reducing its viscosity. This thinner serum phase then drains through the remaining ice cream structure, eventually dripping through the screen upon which the ice cream sits. The ice phase significantly affects all aspects of the meltdown process, including induction time, melting rate, and shape retention at the end of the test (Wu et al. 2019).

Approximately half of the water in ice cream freezes during the dynamic freezing process. This percentage increases to 75%–80% after the hardening stage (Leighton 1927; Julien 1985). Ice crystals in ice cream generally range from 1 to 150 µm in diameter and typically follow a log‐normal distribution (Donhowe et al. 1991; Cook and Hartel 2010). The average crystal size of the commercial and pilot plant scale ice cream falls between 35 and 67 µm (Berger and White 1979; Cook and Hartel 2010; Warren and Hartel 2014). The ice phase structure significantly affects ice cream meltdown behavior (Lomolino et al. 2020; Liu et al. 2023b), specifically related to the ice phase volume and the distribution of ice crystal sizes.

Ice phase volume in ice cream is determined by both total solids content and the freezing point of the formulation. Lower total solids increase ice phase volume and ice crystal size by promoting greater ice formation (Donhowe et al. 1991; Hartel 1996). Additionally, sugars, milk minerals, and other low‐molecular‐weight solutes lower the freezing point through colligative effects, influencing the temperature of ice formation and, consequently, the ice phase volume and crystal size in the final product (Leighton 1927; Goff and Hartel 2013).

Ice phase volume may influence melting, though no consistent correlation has been established between ice phase volume and melting rate. While a higher ice fraction may lead to a slower melting rate and a longer time to completely drip through, this effect has been more commonly reported in studies comparing ice creams with a broader ice content range (30%–70%) and in a simpler system without fat or protein (Liu et al. 2023b; Wang 2024). In contrast, the melting rate remained unaffected by ice volume when other structural components exerted a greater influence on the matrix (Muse and Hartel 2004). This suggests that the meltdown behavior of ice cream is not solely determined by ice crystals but by how all components are arranged and interact within the matrix.

Over and above ice phase volume, the distribution of ice crystal sizes in ice cream, as affected by both formulation and process conditions, may also influence meltdown. Key process conditions influencing ice crystal size include draw temperature (Muse and Hartel 2004; Amador et al. 2017), dasher speed (Russell et al. 1999), as well as freezer and dasher design (Wildmoser et al. 2004; Cook and Hartel 2010; Gallagher 2024). Prolonged residence time in the freezer, achieved by reducing the throughput rate or increasing the hold‐up volume within the barrel, results in larger ice crystals, primarily due to crystal ripening in the freezer barrel (Russell et al. 1999; Drewett and Hartel 2007; Cook and Hartel 2010). Draw temperature can also influence ice crystal size distribution. Higher draw temperature leads to larger ice crystals in hardened ice cream based on relative rates of ice nucleation and growth (Amador et al. 2017). Also, increasing the dasher rotation speed alters ice crystal size. Higher rotational speed raises the product temperature in the freezer due to greater frictional energy dissipation, which promotes the dissolution of smaller crystals and accelerates crystal aggregation, resulting in larger crystals at the freezer exit (Russell et al. 1999; Drewett and Hartel 2007). The dasher design also influences the ice crystal size at the freezer outlet, with larger displacement dashers producing smaller and more consistent crystals based on a reduced extent of recrystallization within the barrel (Gallagher 2024).

Ice crystals that form during ice cream production continue to change during storage through recrystallization, which may also influence meltdown. Recrystallization occurs via four mechanisms: accretion, melt–refreeze, migratory recrystallization, and isomass recrystallization (Donhowe and Hartel 1996). During recrystallization, the total number of ice crystals decreases, while size of individual crystals increases (Hartel 1998). The rate of recrystallization is influenced by storage conditions, including temperature fluctuations and shelf life. Over time, these processes lead to changes in ice crystal size and size distribution, which, in turn, can potentially impact the meltdown behavior of ice cream. When ice cream is stored below its glass transition temperature (−40°C ± −10°C) (Whelan et al. 2008), the structure remains stable, with ice crystals showing minimal size increases (Flores and Goff 1999). When stored under extremely low temperature storage conditions, between −50°C and −70°C, ice crystals only grew slightly (Park et al. 2015). Storing ice cream above about −30°C to −20°C can lead to significant ice crystal growth through recrystallization. Studies have shown substantial increases in crystal size during extended storage, particularly with temperature fluctuations in both premium and low‐fat ice creams (Buyck et al. 2011; Ndoye and Alvarez 2015; Park et al. 2015). After 120 days of storage, recrystallization rates reached a plateau for both types of ice cream (Ndoye and Alvarez 2015). However, these studies did not evaluate the effect of recrystallization on melting.

As with ice phase volume, no consistent correlation has been reported in the literature between ice crystal size and melting rate. Various hypotheses have been proposed, though further investigation is needed. Larger ice crystals may disrupt the structure of the frozen dessert, potentially affecting meltdown properties by creating a less tortuous path for liquid to drain, resulting in a faster melting rate (Muse and Hartel 2004; Daw and Hartel 2015; Lomolino et al. 2020). However, larger ice crystals could also slow the melting process due to their size, requiring more time to fully melt into water and thin the serum phase (BahramParvar et al. 2013; VanWees 2024). Additionally, other factors in the ice cream structure, such as the presence of fat agglomerates in the serum phase (Koxholt et al. 2001) or protein structures (Liu et al. 2023b), can minimize the effect of ice crystal size on melting rate and the overall meltdown process. Similar to the impact of air bubbles, the impact of ice crystals on melting varies depending on whether the ice cream is primarily structured by a fat network or an ice crystal network (Liu et al. 2023b). Ice creams with a fat‐dominated structure generally showed longer lag times, slower melting rates, and lower melted percentages compared to those dominated by ice crystals (Liu et al. 2023b). This suggests that when other structural elements are more prominent, the influence of ice crystal size may be diminished.

Inconsistencies between ice crystal size and melting rate have been reported in the literature, which may be due to changes in other structural elements when the formulation and processing conditions are adjusted. This makes it challenging to isolate the effect of ice crystal size and volume on melting. In order to further understand how ice crystals affect melting, advanced technologies like X‐ray tomography may be needed to track structural changes along with ice crystal melting during the meltdown test (Pinzer et al. 2012).

2.4. Unfrozen Serum Phase

The unfrozen serum phase, which holds the ice cream structure together, typically comprises sweeteners, salt, polysaccharides, and proteins that undergo freeze concentration in the aqueous phase (Goff and Hartel 2013). As the ice cream begins to melt, the freeze‐concentrated serum phase is diluted by the water from the melting ice, resulting in a viscosity decrease. Consequently, the serum phase starts to flow, and the ice cream collapses. In principle, higher viscosity in the serum phase leads to a longer time for the ice cream to drip through due to increased viscous resistance. Additionally, some components in the unfrozen serum phase, especially in such a concentrated aqueous phase, may interact with each other to form a weak gel structure, preventing the melted ice cream from quickly dripping through (Zhang et al. 2018; Wu and Hartel 2024).

Milk proteins can affect meltdown behavior of ice cream by increasing the viscosity in the serum phase. As a macromolecule, protein enhances both the viscosity and shear‐thinning behavior of the ice cream mix, a phenomenon linked to the voluminosity of colloidal particles. The impact on viscosity varies depending on the structure of protein, degree of aggregation, unfolding characteristics, and protein type (Alvarez et al. 2005; Daw and Hartel 2015; Anwar et al. 2022). Micellar casein is particularly effective in increasing viscosity compared to whey protein, owing to its large particle size. Additionally, using high‐pressure treatment on the ice cream mix can induce casein aggregation through calcium‐induced association, further boosting viscosity and improving resistance to melting (Huppertz et al. 2011).

Hydrocolloids play a crucial role as stabilizers in ice cream and frozen dessert products. Commonly employed stabilizers include sodium alginate, carboxymethyl cellulose, carrageenan, gelatin, guar gum, locust bean gum, microcrystalline cellulose, and xanthan gum. These hydrocolloids affect meltdown through three mechanisms. First, they increase the viscosity of the ice cream mix by hydrating and swelling in the aqueous phase, occupying a significant volume in the solution (Phillips and Williams 2009). Different hydrocolloids exhibit distinct abilities to increase viscosity and influence non‐Newtonian behavior, with neutral hydrocolloids generally displaying a greater impact than anionic hydrocolloids in the ice cream mix (Cottrell et al. 1980). Second, certain hydrocolloids, such as xanthan, locust bean gum, and alginate, form a cryogel at freezing temperatures. This cryogel, remaining as a porous structure after the ice crystals melt, may help maintain the structural integrity of the melted ice cream and also may decrease the ability of water from melting ice to diffuse into the freeze‐concentrated serum phase (Goff, Ferdinando, et al. 1999; Patmore et al. 2003; Wu and Hartel 2024). Third, hydrocolloids can interact with proteins in the serum phase through either attractive or repulsive interactions. Opposite charges between proteins and hydrocolloids result in attractive interactions, leading to the formation of either a soluble complex or a two‐phase system through associative separation. This interaction may facilitate the creation of an internal network that preserves the structure and shape of the melted ice cream (Zhang et al. 2018; Lomolino et al. 2020). Conversely, segregative separation occurs when both biopolymers are either uncharged or have the same charges. The concentration of biopolymers in the mix determines the type of system formed. At low concentrations, they can be co‐soluble in the solution, resulting in a one‐phase system. However, at concentrations above a critical level, phase separation occurs, resulting in two phases, one enriched in protein and the other enriched in hydrocolloids (McClements 2006). Particularly in the freeze‐concentrated unfrozen phase, where proteins and polysaccharides are highly concentrated, such phase separation may become even distinct, leaving the polysaccharide that can form a cryogel even stronger due to the phase separation, hindering the melted liquid from dripping through (Wu and Hartel 2024).

Some natural ingredients, such as fruit and tea extracts containing polyphenols, fibers, and pectin, have been incorporated into the ice cream to enhance its nutritional value and functionality. Among the functionalities imparted by these ingredients is the reduction of the ice cream melt rate while maintaining a desirable shape (Hwang et al. 2009; Gabbi et al. 2018; Bilbao‐Sainz et al. 2019). Several hypotheses have been proposed regarding how the components from these extracts contribute to stabilizing the melted ice cream. First, macromolecules like pectin and fiber may adsorb water, thereby increasing viscosity in the ice cream mix (Erkaya et al. 2012; Karaman and Kayacier 2012; Gabbi et al. 2018; Ghandehari Yazdi et al. 2020). In this context, these macromolecules may function similarly to added stabilizers, reducing the melt rate and maintaining shape retention for the melted ice cream. Second, polyphenols from natural sources interact with casein and whey protein in dairy ice cream, forming a protein–polyphenolic network through noncovalent hydrophobic interactions or hydrogen bonding. This network creates a gel matrix capable of trapping various components, such as air bubbles, ice crystals, and fat globules, maintaining its structure even after complete ice crystal melting (Yildirim‐Elikoglu and Erdem 2018; Shadordizadeh et al. 2023; Wicks et al. 2023; Wicks 2024).

3. Rheology and Meltdown

Ice cream undergoes complex and dynamic rheological changes as it transitions from the frozen state to the melted state during the meltdown test. Understanding the intricate connections among the rheology, microstructure, and meltdown behavior of ice cream is essential for comprehensively understanding drip‐through results. Both the rheological and meltdown properties of ice cream are shaped by its microstructural composition and the arrangement of its components within the matrix (Wu et al. 2019; Freire et al. 2020; Liu et al. 2022, 2023b; Liu, Sala, et al. 2024). These elements govern the shift from a semisolid to a semiliquid state during melting. A thorough examination of these factors is necessary to fully explain how rheology, microstructure, and meltdown properties are interconnected.

3.1. Meltdown by Oscillatory Thermorheometry

A small amplitude oscillatory shear (SAOS) temperature ramp can be used to assess melting of ice cream by gradually increasing the temperature from −15°C to 25°C. This method preserves the structural integrity of the ice cream while measuring changes in storage modulus (Gʹ), loss modulus (Gʺ), and the damping factor (tan δ), which is the ratio of Gʺ to Gʹ. These parameters provide insight into the structural changes of ice cream during melting. The elastic properties of the ice cream matrix, which contribute to its initial structure and shape retention as it melts, are reflected in the storage modulus measurement (Gʹ). The following discussion will focus on Gʹ to explore its correlation with melting.

The oscillation thermorheometry (OTR) curves from the SAOS temperature ramp test can be divided into three regions (Wildmoser et al. 2004): Zone I (−15°C to −10°C), Zone II (−10°C to the freezing point, typically around −3°C to −2°C), and Zone III (freezing point of ice cream samples to 25°C), as shown in Figure 3. In the initial phase, below −10°C, ice cream exhibits solid‐like behavior, with the storage modulus (Gʹ) slightly higher than the loss modulus (Gʺ), primarily due to the presence of ice crystals. As expected, more ice phase content correlates with higher Gʹ in frozen product, correlating with reduced scoopability. The average ice crystal size is inversely correlated with Gʹ and Gʺ, as larger ice crystals result in lower Gʹ and Gʺ. This occurs because larger ice crystals have less contact area, reducing ice crystal connectivity and weakening the network (Wang 2024). Other factors, such as the viscosity of the continuous phase, overrun, and fat destabilization, also contribute to the rheological behavior at these temperatures (Goff et al. 1995; Freire et al. 2020). At −15°C, serum phase viscosity has an inverse relationship with Gʹ (Goff et al. 1995; Freire et al. 2020; Liu et al. 2023b). Higher polysaccharide concentration yields a higher serum phase viscosity, but lower Gʹ. The reduction in Gʹ and Gʺ at −15°C in ice creams with higher stabilizer concentrations has been suggested to be due to reduced connectivity among ice crystals, resulting from increased polysaccharide entanglement in the freeze‐concentrated serum phase (Freire et al. 2020; Liu et al. 2023a). Overrun has an inverse correlation with Gʹ at −15°C, meaning higher overrun results in lower Gʹ (Liu et al. 2023a, 2023b; Liu, Sala, et al. 2024). This occurs because the increased volume of air cells reduces interactions between ice crystals, weakening the ice crystal network (Liu, Sala, et al. 2024). Additionally, higher overrun generally produces larger air cells, leading to thinner lamellae and reduced connectivity among ice crystals (Liu et al. 2023b). On the other hand, when other structural elements, such as higher stabilizer levels, dominate the matrix, increased overrun can lead to higher Gʹ at −15°C. This is attributed not only to increased polysaccharide interactions but also to smaller air cell sizes, greater fat destabilization, and enhanced interactions at the serum phase/air cell interface. The higher air surface area in ice creams with greater overrun contributes to a stronger structure and a higher Gʹ at −15°C (Freire et al. 2020). Fat destabilization, however, has little influence on Gʹ as ice cream melts from −20°C to −3°C, particularly in formulations without stabilizers (Liu et al. 2023b). When stabilizers are present, fat destabilization correlates directly with Gʹ at −15°C (Freire et al. 2020). While other structural components affect Gʹ at −15°C, their impact is smaller compared to that of the ice phase (ice crystals and/or ice volume).

FIGURE 3.

Oscillation thermorheometry test of melting ice cream during a temperature sweep from −15°C to 25°C. The melting profile was divided into three zones based on the physical transitions occurring during melting. Gʹ obtained from oscillation thermorheometry for ice cream samples exhibiting two melting patterns—complete drip‐through and remnant melted ice cream foam (remnant foam) at the end of the test—correlated with low and high Gʹ_0°C, respectively. Figure was adapted from Freire (2020).

As the temperature increases, sample enters Zone II, also known as the melting stage in the OTR test. Here, ice crystals begin to melt, with water diluting the serum phase and causing a significant decrease in Gʹ due to the reduction in ice content. The slope of Gʹ during this stage has been suggested as an indicator of the rate of ice crystal melting (Eisner et al. 2005). Ice creams with higher fat content and serum phase viscosity, which showed a slower melting rate in meltdown tests, also exhibited a lower slope of Gʹ (Freire 2020). This correlation suggests that the fat network, formed through fat destabilization, creates a more complex and torturous path for serum phase flow (Liu et al. 2022, 2023a). Additionally, a more viscous serum phase slows liquid drainage during the melting process (Wu et al. 2019; Liu et al. 2023a).

Once the temperature rises above the freezing point and all ice crystals have melted, other structural elements of the ice cream, such as air bubbles, fat, proteins, and polysaccharides, now govern the storage modulus (Gʹ) in Zone III (Granger et al. 2005). These components directly affect the meltdown process, including the melting rate and the extent of shape retention at the end of the test. Gʹ at 0°C (Gʹ_0°C), measured from the OTR test, can be used to assess the elasticity of melted ice cream. Higher levels of fat destabilization, mix viscosity, and overrun result in increased Gʹ_0°C, indicating a more elastic structure in the melted ice cream (Eisner et al. 2005; Freire 2020; Liu et al. 2023b). This is due to a stronger fat network, improved water retention, and greater entanglement of polysaccharides within the matrix. Ice creams with low Gʹ_0°C values exhibited a higher drip‐through rate, while the drip rate decreased exponentially as Gʹ_0°C increased (Freire 2020). Beyond a certain threshold, further increase in Gʹ _0°C had minimal impact on the melting rate (Freire 2020). For melted ice cream to retain its shape, the remaining structure must have enough elasticity to at least partially resist the pull of gravity. Ice creams with low Gʹ_0°C typically lose their shape completely after melting, leaving no structure on the mesh. In contrast, ice creams with high Gʹ_0°C often maintain some foam on the screen after the meltdown test (Figure 3).

3.2. Rotational Rheological Tests on the Melted Ice Cream

Rheology is a valuable research tool for understanding foam properties, as the rheology of a continuous phase fluid of foam often differs from the rheology of the foam itself. For instance, foam viscosity can be several orders of magnitude higher than the continuous phase fluid viscosity (Buzza et al. 1995). Many studies focus on food foam rheology to explore how ingredients affect foam stabilization, using techniques such as SAOS and large amplitude oscillatory shear. These approaches are commonly applied to two‐phase liquid protein foams, such as egg white foams, with or without additional ingredients like sugar, acid, or stabilizers (Ptaszek 2014; Bonilla et al. 2022; Briceño‐Ahumada et al. 2022). Other research has measured the yield stress of foams to correlate it with foam stability (Völp et al. 2021). Since ice cream is a frozen foam system, understanding the rheology of melted ice cream can help shed light on structural collapse during and after meltdown. The measurement of melted ice cream primarily assesses the strength of the internal structure and the flow resistance of the melted liquid, which are key factors driving the melted ice cream to drip through during the meltdown test. The analysis excludes the influence of ice crystals, as previously discussed, since the effect of ice crystals on melting becomes less predominant when other main components are present.

Beyond traditional OTR tests, rotational rheological tests provide valuable insights into the structural changes and mechanisms involved in the meltdown test. In this context, the rheological tests are used to correlate the drip‐through and structural collapse processes from the meltdown test rather than the ice cream melting process, as the ice cream is evaluated in its melted state. These rotational rheological tests, such as flow ramp, creep, and stress growth tests, examine the structure of melted ice cream foam from different rheological perspectives. The key tests and parameters measured are outlined in Figure 4.

FIGURE 4.

Key parameters obtained from rheological tests for melted ice cream at 0°C: (A) hysteresis loop area, indicating the thixotropic behavior of melted ice cream, calculated from the area between the upward and downward flow ramp curves; (B) yield stress, representing the minimum stress required for the melted ice cream to begin flowing, determined from the peak of the stress growth test curve; (C) residual viscosity, representing the flow resistance of melted ice cream, determined by fitting creep test data to a Six‐Element Model, a simplified and precise version of the generalized Kelvin–Voigt model. Figure was adapted from Freire (2020).

The hysteresis loop area, commonly referred to as thixotropic property, is measured by applying a large deformation to melted ice cream while gradually increasing and then decreasing the shear rate (Karaca et al. 2009; Rossa et al. 2012; Aboulfazli et al. 2014). The area of the hysteresis loop measured during the up‐and‐down flow ramp test at 0°C (Hyst_0°C), as shown in Figure 4A, reflects the initial structure of ice cream, which is built by the fat network, air, and serum phase properties (Freire et al. 2020). A larger Hyst_0°C indicates a stronger initial structure in the ice cream, which is related to the induction time during the meltdown process, whereas a low Hyst_0°C corresponds to a weaker structure and shorter induction time (Freire 2020). As Hyst_0°C increases slightly, there is a significant rise in induction time, but further increases result in only minor changes. This pattern suggests that ice cream with a weaker structure offers fewer barriers for the diluted serum phases, leading to a faster release of the first melted drop compared to ice cream with a stronger initial structure.

The yield stress (σ_y) of melted ice cream, which represents the minimum force required for it to flow, can be measured through stress growth tests (Figure 4B). This measurement provides insight into the relationship between the structure of ice cream and the force needed to initiate flow and drip. When the gravitational force surpasses the yield stress of the foam, it triggers irreversible bubble rearrangements, leading to the viscous flow of the foam (Briceño‐Ahumada et al. 2022). Typically, a stronger structure, such as one with more partially coalesced fat globules, results in a higher yield stress. When yield stress is low, the melting/drip‐through rate is high. However, even a slight increase in yield stress leads to a significant reduction in the drip‐through rate, following an exponential decay trend. Beyond a certain threshold yield stress, the drip‐through rate stabilizes at a very low level (Freire 2020). Therefore, strengthening the matrix to increase yield stress offers a way to control the drip‐through rate.

In addition to using yield stress to correlate with the drip‐through rate, the residual viscosity (η ₀) from a creep test provides another way to examine the relationship between structure and the drip‐through process (Figure 4C). Residual viscosity reflects the flow resistance of the melted ice cream, with higher η ₀ indicating greater resistance to flow and drainage, resulting in a slower drip‐through rate. As η ₀ increases to a certain threshold, the drip‐through rate decreases exponentially. Beyond this point, the drip‐through rate stabilizes at a consistently low level (Freire 2020).

When the meltdown process reaches a stationary stage, the remaining ice cream forms a concentrated foam, with most of the liquid having drained during the fast‐melting phase. While the rheology of melted ice cream does not fully represent the foam structure at the end of the meltdown test, it still provides insights into the final body retention. A stronger structure, as indicated by rheological measurements, leads to better retention. Rheological parameters such as yield stress, hysteresis loop area, or residual viscosity all correlate well with the amount of remnant foam, with higher values indicating a stronger structure and improved body retention. Since the rheological and meltdown characteristics of ice cream are influenced by its microstructure and the organization of its components inside the matrix, the relationship of rheology and meltdown behavior remains complex and not yet fully understood, thereby necessitating further research to elucidate the underlying mechanisms and their practical implications.

4. Meltdown and Sensory Analysis

Ice cream melting in the mouth differs significantly from melting in a static meltdown test at room temperature. Although some studies have attempted to link the oral melt rate with the drip‐through measured in meltdown tests, no significant correlation has been found (Guinard et al. 1997; Warren and Hartel 2014; Tolve et al. 2024). In a meltdown test, ice cream melts under controlled conditions, at a set temperature and/or humidity, with a wire screen separating the drip‐through liquid and the melted ice cream foam. The melted ice cream drips due to gravitational force, with the test focusing on factors like the drip‐through rate (liquid released during melting) and the stability of the structure (whether it holds its shape or collapses). In contrast, melting in the mouth occurs under dynamic conditions, where the ice cream is exposed to body temperature—typically higher than the temperature in a meltdown test—and manipulated by the tongue and diluted by saliva. This process accelerates melting, making oral processing a key factor in the dynamic sensory experience of ice cream (Doyennette et al. 2019). Mouthfeel, coating sensation and flavor release, is closely linked to how the ice cream melts in the mouth. This melting process is influenced not only by temperature but also by the interaction between ice cream, saliva, and the mechanics of chewing. Measuring the lubrication properties of ice cream may provide a better indication of its meltdown behavior in the mouth than the traditional meltdown test (Liu, Sala, et al. 2024).

5. Future Work

While significant progress has been made in understanding the factors influencing ice cream meltdown, several challenges and opportunities remain for future research. Current studies have primarily focused on the effects of formulation, processing conditions, and structural characteristics on meltdown behavior. However, there is still a need to explore the interplay between these factors in more depth, particularly in the context of emerging ingredient technologies, evolving consumer preferences, and growing sustainability demands.

As discussed earlier, fat plays a key role in ice cream meltdown behavior, with its size and form making a significant difference. When most of the fat remains as individual globules, the ice cream melts quickly and tends to collapse into a dome shape. In contrast, a higher degree of fat destabilization improves melt resistance, allowing the ice cream to retain its shape even after 6–8 h in a meltdown test. This suggests an opportunity to explore alternative particles, such as starches and proteins, that could similarly influence meltdown behavior by modifying their size within the ice cream matrix. Such an approach could help enhance melting stability in low‐fat and nonfat ice cream products, offering a healthier option without compromising melting property.

Hard‐pack ice cream, soft‐serve ice cream, and ice cream sandwiches are typically formulated differently and undergo different processing conditions, which can influence their meltdown behavior. Additionally, the melting resistance requirements vary by type—for example, soft‐serve ice cream is designed to melt quickly, while ice cream sandwiches must maintain their structure during temperature fluctuations. For hard‐pack ice cream, shrinkage during temperature changes is also a consideration. Despite these differences, little research has explored how formulation and processing conditions impact the structural properties of various ice cream types and, in turn, affect their structural stability and meltdown behavior. Further investigation in this area along with the effect of storage on the meltdown properties of ice cream could provide valuable insights for optimizing product stability to meet specific functional requirements.

The unfrozen serum phase plays a crucial role during meltdown, yet its properties remain difficult to quantify. Attempts have been made to mimic this phase by preparing highly concentrated sugar solutions to measure viscosity (Wang 2024). However, incorporating proteins into such solutions is challenging due to their limited solubility at high sugar concentrations. Further research is needed to accurately quantify the viscosity and evolution of the unfrozen serum phase, especially when additional components like hydrocolloids are present. Advanced techniques like X‐ray microtomography or cryo‐confocal microscopy could provide deeper insights into the role of the unfrozen serum phase throughout the melting process.

Sustainability has become increasingly important in ice cream production. One approach to reducing energy consumption is storing ice cream at higher temperatures. However, as mentioned earlier, ice cream stored at higher temperatures undergoes changes more rapidly than when kept at lower temperatures or below its glass transition temperature. This can affect its melting properties, posing a challenge for this sustainability‐driven approach. Future research could focus on developing formulations that maintain melt resistance while allowing for storage at higher temperatures.

6. Conclusion

The microstructure of ice cream significantly affects its meltdown properties, influencing both the rate and behavior of melting. Structural elements, such as air bubbles and fat networks, play a key role by regulating the flow of melted liquid through lamella and stabilizing the internal structure. Fat destabilization creates a fat network that supports and holds air bubbles and the serum phase in place. The thickness of the lamella is determined by the presence of air bubbles, while its complexity, or tortuosity, is primarily influenced by ice crystals. Additionally, the unfrozen serum phase impacts meltdown by altering viscosity and potentially forming a gel that helps maintain the structural integrity of product.

Understanding the relationship between microstructure and meltdown is crucial for optimizing product development and ensuring quality. The meltdown behavior of ice cream, alongside qualities such as texture, mouthfeel, and overall enjoyment, is determined by both the complex microstructure and composition of the product, which ultimately affect consumer satisfaction. Moreover, meltdown control is essential for maintaining product stability during distribution and storage, where temperature fluctuations can compromise quality. Manufacturers can improve product resilience in various environments by adjusting formulations and processes to manage meltdown more effectively. For example, in high‐fat ice cream, the fat network effectively provides melt resistance. In low‐fat ice cream, where fat is insufficient to maintain structure, modifying other structural elements such as the serum phase, ice crystals, and air cells can achieve melt resistance comparable to that of full‐fat ice cream.

This review highlights the importance of ongoing research into ice cream meltdown, particularly in light of advancements in technology and processing techniques. Continuous exploration of the interaction between microstructure and meltdown is vital for driving innovation, meeting evolving consumer expectations, and maintaining high standards in frozen dessert science.

Author Contributions

Biqing Wu: writing – original draft, writing – review and editing, visualization, conceptualization. Didem Sözeri Atik: writing–original draft, writing – review and editing. Dieyckson O. Freire: writing – original draft, writing–review and editing, visualization. Richard W. Hartel: investigation, writing – review and editing, supervision, resources, conceptualization.

Conflicts of Interest

The authors declare no conflicts of interest.