Malolactic fermentation in wine - beyond deacidification

Introduction, 589 2. Citrate fermentation, 589 3. Metabolism of carbohydrates, 590 3.1 Metabolism of mono‐ and disaccharides, 590 3.2 Metabolism of polysaccharides, 591 3.3 Metabolism of polyols, 591 4. Catabolism of aldehydes, 592 5. Hydrolysis of glycosides, 592 6. Degradation of phenolic acids, 593 7. Synthesis and hydrolysis of esters, 593 8. Lipolysis, 593 9. Proteolysis and peptidolysis, 593 10. Amino acid catabolism, 594 11. Sensory impact, 595 12. Health implications, 595 12.1 Formation of amines, 595 12.2 Formation of ethyl carbamate precursors, 595 12.3 Formation of glyoxal and methylglyoxal, 596 13. Conclusions, 596 14. References, 596 Malolactic fermentation (MLF) in wine is a secondary fermentation that usually occurs at the end of alcoholic fermentation by yeasts, although it sometimes occurs earlier. It is practically a biological process of wine deacidification in which the dicarboxylic L‐malic acid (malate) is converted to the monocarboxylic L‐lactic acid (lactate) and carbon dioxide (Davis et al. 1985). Deacidification is particularly desirable for high‐acid wine produced in cool‐climate regions, such as New Zealand and Canada. This process is normally carried out by lactic acid bacteria (LAB) isolated from wine, including Oenococcus oeni (formerly Leuconostoc oenos; Dicks et al. 1995), Lactobacillus spp. and Pediococcus spp. (Wibowo et al. 1985). Various technologies, such as bioreactors with high‐density cells and immobilized cells or enzymes, have been developed to facilitate wine deacidification (Maicas 2001). Oenococcus oeni is the preferred species used to conduct MLF due to its acid tolerance and flavour profile produced. In addition to its occurrence in wine, MLF occurs in other fermented beverages, such as cider (Carr 1987; Jarvis et al. 1995).