Effects of pH and Total Acidity on Male-lactic Fermentation in Wine

Bousbouras, George Elias
Major Prof
Kunkee, R.E.

Malo-lactic fermentation is a bacterial secondary fermentation in wine which converts dicarboxylic malic acid to the monocarboxylic lactic acid. The rate depends on many variables. The formula of malo-lactic fermentation can be thought of as a complex differential equation with numerous independent variables, many of which are still unknown. New information on the complexity about some of these variables should enable winemakers to have better control of the fermentation. Early investigators recognized a change in wine brought about by bacteria that resulted in production of lactic acid, but also often brought about a reduction of total acidity (Pasteur, 165d; Balard, 1061). It is assumed that, although this fermentation was only recognized a little over one hundred years ago, it has occurred in wines since the beginning of winemaking itself. In the last few decades, due to its great importance in winemaking, this secondary fermentation began to be studied thoroughly. For an enologist, this secondary fermentation provides a large number of opportunities for study. Along with the conversion of slate to lactate there arises new sensory constituents in wines. The change in pH creates different conditions for the state of color and tartrate stability of the wine. The malo-lactic fermentation results in an acidity decrease which can result in desirable or undesirable properties for the wine. The fermentation may provide either an increase in complexity of the flavor or add off-flavors. Also, there is a reduction in chelating compounds by loss of malic acid and citric acid. The latter reduction would tend to encourage oxidative reactions in wine. Gassiness is produced during the fermentation and it is an indicator of instability in bottled wine. The appearance of male-lactic fermentation may take place very soon after alcoholic fermentation or it may appear months or years later, even after the wine has been bottled. In conclusion, the general aspects of malo-lactic fermentation in wines pose an interesting question. How important is the original pH and total acidity of the wine, before malo-lactic fermentation, on the rate of malo-lactic fermentation and on the development of desirable or undesirable effects of the fermentation? The work presented here, entitled the "Effects of pH and Total Acidity on Malo-lactic Fermentation in Nine" is an attempt to answer this question.