Page 20 - MALOLACTIC FERMENTATION – IMPORTANCE OF WINE LACTIC ACID BACTERIA IN WINEMAKING

MALOLACTIC FERMENTATION IN WINE
Historically, MLF was not well controlled in wine production, and its effect was often less than desirable. If MLF proceeded to completion without imparting flavours uncomplimentary to the organoleptic profile of the wine, MLF was considered a success. Current wine produc- tion techniques are much more sophisticated, as are the strains of wine lactic acid bacteria available to the winemaking community. The impact on wine flavour from MLF can now be attributed to the way the wine LAB either modify the existing flavour compound precursors, which occur naturally in grape juice and wine, or to the production of specific flavour com- pounds as the bacteria grow in the product. Indeed, winemakers are now capable of “sculpt- ing” wines by making use of specific bacteria and their ability to modify the aroma, texture, mouthfeel and organoleptic profile of the product.
The impact of MLF on the body of wines can be attributed to the decarboxylation reaction itself, as well as to the formation of metabolic by-products. When MLF occurs, the dicarbox- ylic acid, L-malic acid, is converted to the monocarboxylic acid, L-lactic acid. There will be a concomitant increase in pH because of the conversion of one of the acidic carboxyl groups of malic acid into CO2. On average, after MLF is complete, the pH will increase by approximately 0.2 units. This tends to make the wine less acidic, softer and texturally more pleasing in the mouth.
As a result of the growth of MLB in wine, it is often felt that a degree of biological stability toward bacterial growth is imparted. Winemakers generally feel that once their wine has successfully passed through MLF, clarification and stabilization of the product can be per- formed. The use of selected MLB strains in the winemaking process has played a large role in achieving early biological stability for the product. These strains of wine LAB have been well researched and exhaustively catalogued. They confer upon the winemaking process the same degree of reliability and predictability as the known strains of active dry wine yeast, which are routinely used to conduct the alcoholic fermentation (AF).
In the past, MLF has been used mainly in the production of red wines, and sometimes in the production of white wines. In white wine production, MLF is usually used to lower the acidity of wines produced in cool climates or to confer a degree of organoleptic complexity to such lesser-flavoured white varieties as Chardonnay. Recent research has begun to explore the effects of MLF on white wines from varied viticultural regions. The malolactic organisms are subject to the same growth necessities in white wine as in red wine, but when they interact with the components of the white wine matrix, the products they form can vary. This is very interesting and helpful, because it can aid the winemaking community in its quest to craft a product with a unique, pleasing and characteristic organoleptic profile.
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