The Biology of Malolactic “Bugs”

In this excerpt from the technical binder “Malolactic Fermentation in Wine” (Lallemand, 2005) written for commercial winemakers, researchers at Lallemand, Inc. offer an insider’s view of the more technical aspects of malolactic fermentation (MLF). Lactic acid bacteria (LAB) are natural inhabitants of vineyards and wineries. These bacteria can transform malic acid into lactic acid. Wild LAB may not completely degrade all the malic acid in wine must and may additionally produce off aromas or flavors. However, specially selected strains of LAB, such as certain strains Oenococcus Oeni, are the desired microorganisms for performing a successful malolactic fermentation. Lactic acid bacteria (LAB) are found naturally on grapes, leaves, soil and equipment surfaces and have the ability to grow on a variety of sources, including grape juice. The most common LAB belong to the genera Lactobacillus, Pediococcus, Leuconostoc and Oenococcus. These bacteria are generally microaerophillic (they respire anaerobically, but are stimulated by small amounts of oxygen), require carbohydrates and must be supplied with amino acids and vitamins in order to proliferate. Wild or cultured LAB may cause a malolactic fermentation in wine.