Page 19 - MALOLACTIC FERMENTATION – IMPORTANCE OF WINE LACTIC ACID BACTERIA IN WINEMAKING

WINE SENSORY COMPONENTS AND MALOLACTIC FERMENTATION
RICH MORENZONI, PH.D.
Malolactic fermentation (MLF) is the well-documented decarboxylation of L-malic acid to L-lactic acid and CO2 by wine lactic bacteria (LAB). It is a biological process conducted by a living organism, which means that lactic acid and CO2 are not the sole end products of the reaction. The causative bacteria cannot grow on L-malic acid as the only carbon source. They require carbohydrates and nitrogen, as do all living organisms. These bacteria derive the majority of energy for growth by metabolizing the various sugars present in grape juice and/ or wine. The decarboxylation of malic acid supplies only a very small amount of the energy required to sustain microbial growth. As a corollary to the bacterial metabolism of carbohy- drates and amino acids, a variety of metabolic end products can be produced. Some of the compounds produced have pleasing organoleptic and sensory properties, while some do not. Recently, Sumby et al. (2013) have demonstrated the presence of esterases in wine MLB and have clearly shown they can modify the ester profile during the course of MLF in wine. The success and usefulness of selected MLB strains rest in their ability to produce desired products with minimal or no production of undesirable products. Malolactic bacteria possess the ability to affect wines in a positive way, both texturally and sensorially.
The most common wine LAB currently in use is Oenococcus oeni. Many strains of this organ- ism are available, and they can affect the organoleptic profile as well as the body and texture of wine. Some common terms used to describe the positive effects of MLF on wine flavour are nutty, toasty, buttery, fruity and spicy. These descriptors can be attributed to the produc- tion of flavour-active compounds, or to the modification of existing flavour components. In addition, the body of the wine can be affected, making it softer and richer.
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