Malo-lactic fermentation, inhibition

Practical and fundamental aspects of malo-lactic fermentation are given. Conditions which winemakers can use for better control of the fermentation, including detailed procedures for inoculation with Leuconostoc oenos ML 34 and for inhibition with fumaric acid, are presented. New information on the role of malic acid decarboxylation in bacterial metabolism and on the enzymatics of malic acid decarboxylation are reviewed. The malic acid decarboxylation seems to involve two pathways a direct decarboxylation of malic to lactic acid with NAD as a coenzyme and a concurrent but small oxidative decarboxylation to pyruvic acid and NADH. How these pathways can bring about the marked stimulation of bacterial growth rate by the malo-lactic reaction and their negligible effect on growth yield are discussed. 

San Joaquin Valley (Calif.) table wines (wines with less than 14% ethanol) represent about 80% of wine production in California. In two large wineries there, the malo-lactic fermentation is inhibited and does... 

Fumaric Aero Inhibition. Another means of preventing malo-lactic fermentation is to add fumaric acid after alcoholic fermentation is complete (45, 46, 47,48). The inhibition is relative and its extent is dependent on the amount added. The susceptibility to fumaric acid is also dependent on the strain of malo-lactic bacteria tested (49). However, we know of no case where fumaric acid addition at the levels suggested by Cofran and Meyer (45) (about 0.05%) did not delay malo-lactic fermentation under normal winemaking conditions. This includes several experiments from our pilot winery (50). Nevertheless, we have not been hasty to recommend the use of fumaric acid as an inhibitor because 1) of the difficulty in solubilizing the acid in wine 2) we do not know the mechanism of action of its inhibition [Pilone (47, 48) has shown that the bacteria metabolize low levels of fumaric acid to lactic acid but, at inhibitory levels at wine pH, the acid is bactericidal] and 3) of the desirability of minimizing the use of chemical additives. 

Malo-Lactic Fermentation. The bacterial conversion of malic acid to lactic acid usually does not occur in North Coast white wines because of low pH, high S02, and cool storage temperatures, factors that inhibit lactic acid bacteria activity. Some work has been done in the North Coast with malo-lactic fermentation in Chardonnay, following the traditional practices in Burgundy. Factors used to encourage experimental malo-lactic fermentation in white wines have been bacterial inoculation, warmer (18°-21° C) fermentation temperatures, prolonged lees contact, and low free-S02 levels until fermentation is complete. 

Gerbaux, V., VUla, A., Monamy, C. Bertrand, A. (1997). Use of lysozyme to inhibit malo-lactic fermentation and to stabilize wine after malolactic fermentation. Am. J. Enol. Vitic.,48, 49-54. 

The inhibition of malo-lactic fermentation can be obtained by SO2 (/w30 mg/liter), maintainance of storage temperature at less than 18°C and adjustment of pH to at least below 3.3. Killing or removing the bacteria from wine is a more definite step to stabilize wine against malo-lactic fermentation. Pasteurization and particularly HTST treatment (high temperature, short time -98 C for one second - with rapid cooling) is often used. Sterile filtration has also been used with 0.45 (un membrane filters. 

Pilone, G.J., B.C. Rankine, and D.A. Pilone. 1974. Inhibiting malo-lactic fermentation in Australian dry red wines by adding fumaric acid. Am.J. Enol. Vitic. 25 99-107. 

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