Spoilage, acetic

Table 8.3 Conventional and rapid detection and characterisation methods for heer spoilage acetic acid bacteria, Zymomonas, and Enterobacteriaceae species...

Some of the volatile substances which are produced during fermentation, like acrolein, diacetyl, 2-butanol, allyl alcohol, or acetic acid, are a result of enhanced microbiological activities and may cause an unpleasant flavour (off-flavour) at certain levels thus, elevated concentrations of such compounds are markers for spoilage of the raw material, negative microbiological influences during or after the fermentation process, or a poor distillation technique. 

Volatile Acidity. Acetic acid is the primary acid formed during wine spoilage. Legal limits for it exist in all wine-producing countries, varying from 0.10 to 0.25% exclusive of sulfur dioxide and sorbic acid. The United States and California State limits are among the lowest. Good... 

Acetic acid content is used as a criterion for aerobic bacterial spoilage in wines. We can easily analyze two wines and determine that one has a lower volatile acidity than the other. But by every available standard of product quality judgment, the wine with the higher level of acetic acid may be the superior product. It is no accident that Subpart ZZ, Part 240, Title 26 of the Code of Federal Regulations allows the direct addition of acetic acid to correct natural deficiencies in grape wine. As sanitation practices have improved, the so-called natural acetic acid content diminished, and this has been correlated with lower consumer acceptance in certain cases (2). 

Unfortunately, uncontrolled MLF also presents a risk of wine spoilage by compounds that can produce off-flavours (including acetic acid, volatile phenols and mousiness) or that may be hazardous to human health (such as ethyl carbamate and biogenic amines). The most important aspects of the development of LAB and MLF in wines are dealt with in this chapter. 

When alcoholic fermentation is too slow or when it stops, conditions are favourable for bacterial development. LAB ferment different quantities of sugars that have not been totally fermented by yeasts and produce acetic acid and D-lactic acid. This alteration is called Lactic disease" (piqure lactique) and is characterised by a high volatile acidity that depreciates the wine. If this volatile acidity exceeds the limit of 1 g/L, the wine is unmarketable (Lonvaud-Funel 1999). This spoilage also occurs in fortified wine where O. oeni, L. hilgardii, L. fructivorans and L. plantarum are active in spite of very high ethanol contents. 

Acetic acid represents the only organic acid of normal olfactory sensory significance to wines (27). While acetic acid may be formed by . cerevisiae, the concentrations produced are typically less than 300 mg/L (55), far lower than the concentrations produced by spoilage microorganisms (he, Acetobacter) which are the predominate source (52). Apiculate yeasts may also serve as a source of acetic acid Romano et ah (36) found that Kl apiculata typically produced greater than 200 mg/L acetic acid in synthetic medium fermentations. 

A major cause of wine spoilage by AAB is the production of excessive acetic acid. The legal limit for acetic acid in wine is 1.2-1.4 g/L, concentrations that also greatly reduce wine quality (Drysdale and Fleet, 1989a Sponholz, 1993). Drysdale and Fleet (1989a) reported that as much as 50-60% of the ethanol content of a wine could be oxidized by these bacteria with the production of 1.5-3.75 g/L of acetic acid. 

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