Cider sickness, caused by infection through Zymomonas anaerobia is now very uncommon, as it is countered by the lower pHs (<3.5) and reduced tendency to have residual sugar in the product. Symptoms include an aroma of banana skins and a white turbidity due to the acetaldehyde produced reacting with polyphenols to form insoluble complexes.
Mousiness in cider is due to isomers of 2-acetyl or ethyl tetrahydropyridine (Fig. 5.6) produced by lactic acid bacteria or Brettanomyces under aerobic conditions. Detection of the flavour depends on reaction of the compounds with saliva, with the acidity of the saliva releasing the compounds from the base forms where they are not detected. Thus, simple smelling of cider will not tell whether there is a problem or not.
Ropiness in cider is due to the production by lactic acid bacteria of a polymeric glucan that increases the viscosity of the cider, which appears to be oily when poured due to the movement of the slimy glucan.
Lactic acid bacteria may also break down glycerol. They produce 3-hydroxypropanal which spontaneously dehydrates to generate acrolein that has a bitter taste and a pungent aroma (Fig. 5.7).
Chill hazes in cider are due to complex formation between polyphenols and polysaccharides, and to a lesser extent, with the very low levels of proteins. This is promoted by iron and copper, the levels of which should be minimised.
Fig. 5.6 A source of mousiness in cider.
3-Hydroxypropanal Fig. 5.7 A source of pungent bitterness in cider.
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