Table 2.

Common beer spoilage species and their effects on beer.

Stage of brewing process	Spoilage organismb	Information	Literature
Brewing raw materials	Aspergillus fumigatus	Off-flavours: roughness and stale	Vaughan et al. (2005)
	Fusarium culmorum	Production of mycotoxins, gushing inducer	Laitila et al. (2002)
	Fusarium graminearum
Mashing & wort separation	Ped. pentosaceus	No defect in finished beer detected	Simpson and Taguchi (1995)
	Bacillus coagulans	Formation of lactic acid and nitrosamine	Smith et al. (1992)
	Rahnella aquatilis	Undesirable formation of diacetyl & dimethyl sulphide (DMS)	Van Vuuren et al. (1980)
	Citrobacter freundii	Notable off-flavours and aromas. Production of diacetyl, DMS, acetoin, acetaldehyde, lactic acid and 2,3-butandiol	Van Vuuren et al. (1980)
	Klebsiella terrigena	High concentrations of DMS	Van Vuuren et al. (1980)
	Klebsiella oxytoca
Fermentation	Ped. inopinatus	Longer fermentation times, production of diacetyl	Priest and Campbell (2003)
	Selenomonas lacticifex	Relatively strong beer spoilage potential	Schleifer et al. (1990)
	Zym. paucivorans	Poorly characterised as a beer spoilage microorganism. Reported to not grow in beer at pH 4.6 and at ethanol concentrations <5% (w/v)	Schleifer et al. (1990); Suzuki (2020)
	Zym. raffinosivorans	Spoilage activity similar to Pectinatus spp., turbidity, production of H2S and “rotten-egg” smell	Jespersen and Jakobsen (1996)
	Rahnella aquatilis	Notable off flavours and aromas from production of diacetyl, DMS, acetoin, acetaldehyde, lactic acid and 2,3-butandiol	Van Vuuren et al. (1980)
	Obesumbacterium proteus	Inhibit fermentation, increased beer pH, production of acetoin, lactic acid, propanol, DMS, isobutanol and 2,3-budandiaol Parsnip-like off-flavour and aroma	Priest et al. (1974)
	Non-Saccharomyces*	Slow or stuck fermentations, superattenuation. Final beer: turbid, off-flavours & aromas	Lawrence (1988)
	Saccharomyces spp.**
Ageing, Filtration, Pasteurisation & packaging	Meg. cerevisiae	Risk to no and low alcohol beers. Unpleasant odours. Formation of acetoin, hydrogen sulphide, butyric, acetic, caproic, isovaleric and valeric acids.	Back (2005)
	Pect. cerevisiiphilus	Haziness reported, produce vast amounts of acetoin, hydrogen sulphide, acetic and propionic acids. Sour taste, “rotten-egg” smell	Paradh et al. (2011)
	Pect. frisingensis
	Lactobacillus spp.	Hazing or ropiness, sourness, undesirable flavours, and aromas	Suzuki (2015)
	Pediococcus spp.
Contaminants of final product	P. damnosus	Off-flavours: production of diacetyl and lactic acid. Turbidity, acidity, gas production, ropiness	Sakamoto and Konings (2003)
	P. inopinatus	Minor beer spoilage potential	Iijima et al. (2007)
	L. brevis	Turbidity, acidity, superattenuation, gas production and off flavours	Suzuki (2011a)
	L. casei	Diacetyl off-flavour in final beer	Suzuki (2015)
	L. coryneformis
	L. plantarum
	Meg. cerevisiae	Production of butyric acid, H2S, and small amounts of C-5 and C-6 fatty acids. Turbidity and unpleasant off-flavours	Juvonen (2015); Paradh et al. (2011)
	Mic. kristinae	Uncommon aroma of fruitiness in beer	Back (1981)
	Z. mobilis	Production of large quantities of acetaldehyde and hydrogen sulphide. ‘Fruity’ and ‘sulphidic’ aroma characteristics	Anderson and Howard (1974); Dadds et al. (1971)
Dispense	A. aceti	Haziness, acidification (lactic and acetic acid strains), production of diacetyl, unpleasant phenolic, buttery, rotten egg and atypical fruity aromas	Quain (2015)
	A. pasteurianus
	G. oxydans
	Lactic acid bacteria
	Wild yeasts

^aThe information is summarised from the literature cited in the table. ^bL., Lactobacillus, Meg., Megasphaera, P., Pediococcus, Pect, Pectinatus, Mic., Micrococcus, Z, Zymomonas, Zym, Zymophilus. *Non-Saccharomyces wild yeasts include organisms of the genera Brettanomyces, Candida, Debaryomyces, Dekkera, Filobasidium, Hanseniaspora, Kluyveromyces, Pichia, Torulaspora, Zygosaccharomyces. **Saccharomyces wild yeasts primarily include three species, S. cerevisiae, S. bayanus and S. pastorianus.