Sulfur dioxide yeast inhibition

In principle, the same carbohydrates and their degradation products formed after hydrolysis of wood can be recovered from sulfite spent liquors. However, this requires complicated and expensive separation techniques. The industrial use of sulfite spent liquor components is mainly limited to fermentation processes. The most common product is ethyl alcohol which is produced from hexose sugars by yeast (Saccharomyces cerevisae) and separated from the mixture by distillation. Even the carbon dioxide formed in the process can be recovered. Other fermentation products, including acetone, n-butanol, and lactic acid, can be produced by certain microorganisms. Because some contaminants, for example, sulfur dioxide, inhibit the growth of the yeast, they must be removed from the liquor prior to the fermentation. 

Sulfuric acid is one of the most traditional antimicrobial substances, widely employed in products such as wines. It is soluble in water and gives sulfurous acid and its ions when it comes into contact with water in foods. The ions percentage increases with the reduction of pH value. Sulfuric acid salts can be used as preservatives and are more useful since they are available in dry forms. The antimicrobial action against yeasts and moulds and bacteria is selective, with certain species to be more sensitive in inhibition compared to other species. Bacteria are generally more sensitive in inhibition. Sulfur dioxide and sulfuric acid salts are GRAS substances however, their level of use in wines is restricted to 0.035%. Its presence at higher levels lead to undesired taste and is generally forbidden in foodstuffs that are considered as sources of thiamine due to the fact that they inactivate... 

In addition to common soil and plant bacteria that do not persist in wine formation, members of the lactic and acetic acid bacterial families can be found on the surface of the grape. These bacteria can pose a problem in wine fermentation, particularly if an antimicrobial agent like sulfur dioxide is not used or if the yeasts are inhibited in their abiUty to dominate the fermentation, allowing other organisms to proliferate. The metaboUc activities of these bacteria often lead to high acetic and organic acid concentrations that can be inhibitory to yeast. 

Terrell, R.R.,J.R. Morris, M.G. Johnson, E.E. Gbur, andDJ. Makus. 1993. Yeast inhibition in grape juice containing sulfur dioxide, sorbic acid and dimethyldi-carbonate./. Food Sci. 58(5) 1132-1135. 

The need for sulfur dioxide in the free state was pointed out by Hailer (1911), who examined the growth-inhibiting and lethal effects of sulfurous acid, its sodium and potassium salts, and several of its addition compounds, on microorganisms such as those commonly encountered in food products. The bacteria used were found to be very sensitive to the presence of sulfurous acid in the nutrient medium, the yeasts were consider-... 

Cocolin, L. and D.A. Mills. 2003. Wine yeast inhibition by sulfur dioxide a comparison of culture-dependent and independent methods. Am.J. Enol. Vitic. 54 125-130. 

Sorbate has also been implicated as the precursor of a flavor defect in wine that has a geranium character. Sorbate may be added in the winemaking process as a secondary yeast inhibitor to reduce the amount of sulfur dioxide used. While sorbate is a good yeast inhibitor, it does not inhibit the growth of bacteria. Crowell and Guymon [144] have found that certain bacteria in wines can convert sorbate to 2-ethoxyhexa-3,5-diene, which has a geranium character. 

This section covers the phenomenon of inhibition in grape must fermentation. A large number of substances exist that may hinder yeast multiplication chemical antiseptics and antibiotics and fungicides (Rib6reau-Gayon et al., 1975a). Inhibitors used for the conservation of wines (in particular sulfur dioxide) are described in Chapters 8 and 9. 

---