Score plot (A) and loading plot (B) of first and second principal components after principal-component analysis based on volatile components that mainly (P < 0.05) differentiated the four sourdoughs propagated under firm and liquid conditions for 1 (I) and 28 (V) days. The ingredients and technological parameters used for daily sourdough backslopping are reported in Table 1. C2, acetic acid; C6, caproic acid; Me2C3, 2-methyl-propionic acid; 3Mebutanal, 3-methyl-butanal; bzacetald, benzeneacetaldehyde; 2Mepropanol, 2-methyl-1-propanol; 3Mebutanol, 3-methyl-1-butanol; 2Mebutanol, 2-methyl-1-butanol; 3Me3buten1ol, 3-methyl-3-buten-1-ol; 3buten2one, 3-buten-2-one; 3Me2butanon3, 3-methyl-2-butanone; MC2, methyl acetate; Mbzte, methyl benzoate; EC2, ethyl acetate; PC2, propyl acetate; MP2C2, 2-methyl-propyl acetate; MB3C2, 3-methyl-butyl acetate; MB2C2, 2-methyl-butyl acetate; MB3C6, 3-methyl-butyl hexanoate; PheEC2, 2-phenyl-ethyl acetate; DMTS, dimethyl-trisulfide; 3Mefuran, 3-methyl-furan; 2Hxfuran, 2-hexyl-furan; Ether, diethyl-ether; 3EMbenz, 1-ethyl,3-methyl-benzene; 2EMbenz, 1-ethyl,2-methyl-benzene; TriMbenz1, 1,x,y-trimethyl-benzene; TriMbenz2, 1,w,z-trimethyl-benzene; TriMbenz3, 1,3,5-trimethyl-benzene; apinene, alpha-pinene; bmyrcene, beta-myrcene; dcarene, delta-carene; aterpinene, alpha-terpinene; pcymene, p-cymene; MEMbenz, 1(1-methyl-1-ethenyl)-4-methyl-benzene; bpinene, beta-pinene.