1.4. Acid taste

Acid taste is due to excessive amounts of certain acids which are formed during fermentation. Two acids are involved: acetic acid which is volatile and lactic acid which is non-volatile. It should be stressed that there is no connection between the presence of acetic and/or lactic acids and the Free Fatty Acid (FFA) content which is dealt with later.

Appropriate drying will reduce the acidity in the fermented beans, however if this is conducted too quickly the acidity will remain in the cocoa. During manufacture, the acetic acid present in dried beans will normally be reduced to an acceptably low level, but the non-volatile lactic acid remains and if present in excess will cause an off-flavour in chocolate. Furthermore, the presence of excessive acidity usually correlates with poor development of cacao intensity. The presence of acetic acid is readily detected by smelling the beans, but the acidity due to lactic acid can only be detected by tasting cocoa mass samples or chocolate made from them.

A high degree of acidity is usually associated with a pH of 5.0 or less in the dried beans. The pH of cocoa mass prepared from properly fermented and dried West African beans in which the perceived acidity is very slight or absent is around 5.5. Control of pH, however, is not an assurance of good cacao intensity and if measures are taken to raise the pH, by neutralising for instance, they will not achieve an acceptable level of cacao intensity.

For some cocoas, acidity can be reduced by storing the unopened pods for a few days before commencing fermentation (Meyer et al., 1989). However, care must be taken that only undamaged pods are stored to reduce the risk of ochratoxin A formation. Acidity may also be reduced by the combined action of removing about 20% of the pulp prior to fermentation and reducing the fermentation time. The disadvantage of this treatment is that cocoa flavour may not be fully developed, although on balance, limited cocoa flavour development with slightly increased bitterness and astringency may be perceived as a lesser flavour defect than excessive acidity (Schwan and Wheals, 2004).

Although acid taste may be reduced if the fermentation is extended for an extra 4 or 5 days, usually with extra turning of the fermenting beans, this leads to serious off-flavour problems. The pH of the beans is increased but this leads to mould growth and putrefaction and the production of ammoniacal off-flavours mentioned above. Acid taste, which might have been corrected by the manufacturer during processing, is replaced by these much more serious off flavours which make the beans virtually unusable.