Chapter 5 - Lactic acid bacteria and malolactic fermentation in winemaking

Abstract

Wine is an ancient, traditional, and widely popular alcoholic beverage fermented from grapes. Winemaking requires a succession of biotransformations that must be well managed by the winemaker. This involves not only the natural microflora but also, often, selected starters, added to the must or wine at the appropriate time. Microbial resource management has played a central role in the wine industry. There are two different fermentations in the winemaking process. The alcoholic fermentation process is mediated by the metabolic activity of common yeast, Saccharomyces cerevisiae, and the malolactic fermentation (MLF), by that of lactic acid bacteria belonging to the ancient genera-Lactobacillus, Oenococcus, Leuconostoc, and Pediococcus with a predominance of the species Oenococcus oeni. MLF is the process by which certain LAB convert l-malic acid into l-lactic acid and carbon dioxide. This fermentation is essential to produce some red wines, white wines, and sparkling base wines. The softening of the wine, by increasing its pH, is the main function of MLF, and the removal of a microbial carbon source impacts the flavor profile of the finished wines. Several species of lactic acid bacteria (LAB) can undertake MLF, of which O. oeni is one of the species most adapted to the harsh conditions of wine. MLF bacteria have the ability to transport malate into their cytoplasm via a specific malate permease, in addition to passive transport, and produce a cytoplasmic malolactic enzyme responsible for the malic acid decarboxylation. For the success of MLF, the selection of the right bacteria depends on the control of appropriate physico-chemical parameters.