Wine fermentation spoilage

Although sulfite may not be as inhibitory to native yeasts as once believed, prefermentation additions are, nevertheless, crucial in the control of native lactic acid bacteria (LAB) and acetic acid bacteria (AAB). Failure to utilize the agent, at least in the recent history of some California red wine fermentations, has been one step implicated in rapid proliferation of spoilage LAB, the metabolites of which are strongly inhibitory toward both indigeneous and inoculated strains of Saccharomyces sp. (see Sec 1.4.1). 

Among Pasteur s many contributions to the wine industry were several simple methods of wine analysis, and his research has had a permanent influence on the wine industry. As a well-trained chemist he was certain that chemical analysis would reveal the nature of the process of alcoholic fermentation and the type and degree of spoilage related to it. In both cases he was correct. 

Daily sugar and temperature readings were made. For red wines, the fermentation lasted 5-7 days and the wine was drawn off the pomace essentially dry. If raisins or half-dried grapes are present, the fermentation ceased with 1-4 percent residual sugar and lactic bacterial spoilage ensued. Such wine should be distilled, he recommended. He added that if blended with other sound wine, it will contaminate that wine as well. 

Vinegar is one of the oldest known fermentation products, predated only by wine and possibly by certain foods from milk. First derived from the spoilage of wine, vinegar has been used as a condiment, food preservative, medicinal agent, primitive antibiotic, and... 

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. 

Brettiness". "Volatile phenols can be considered as natural components in wines and beer, or as spoilage compounds when present in excessive amounts" (84). Brettanomyces species can produce both mousiness and, at low concentrations of volatile phenolics, also "a distinct aroma described variously as cider-like, spicy, dove-like or phenolic... formed toward the end of fermentation" (84). The ethyl phenols produced can exceed the sensory threshold 16-fold (85), producing wines, at high concentrations of volatile phenolics, with distinct "barnyard", "stable", and "animal" phenolic odors (85-87). Wines with high concentrations of phenolic odors are deemed "Bretty" by tasters. 

Trioli, G. In Survey of studies in Italy on management offactors affecting alcoholic fermentations, Wine Spoilage Microbiology Conference Fresno, CA 1996 pp. 42-43. 

---