Malo-lactic fermentation control

The bacterial conversion of malic acid to lactic acid and carbon dioxide has been recognized since 1890 and is referred to as the malo-lactic fermentation. This conversion has been promoted under controlled conditions in the cooler viticultural regions of the world where grapes mature with excessive amounts of malic acid which causes taste imbalance... 

Practical and fundamental aspects of malo-lactic fermentation are given. Conditions which winemakers can use for better control of the fermentation, including detailed procedures for inoculation with Leuconostoc oenos ML 34 and for inhibition with fumaric acid, are presented. New information on the role of malic acid decarboxylation in bacterial metabolism and on the enzymatics of malic acid decarboxylation are reviewed. The malic acid decarboxylation seems to involve two pathways a direct decarboxylation of malic to lactic acid with NAD as a coenzyme and a concurrent but small oxidative decarboxylation to pyruvic acid and NADH. How these pathways can bring about the marked stimulation of bacterial growth rate by the malo-lactic reaction and their negligible effect on growth yield are discussed. 

To show correlation between occurrence of malo-lactic fermentation and bacterial inoculation, and to show consistency of results among the control lots and inoculated lots, it is imperative that the division of lots be made before alcoholic fermentation. For red wines, great care must be taken to obtain equitable distribution of the crushed grapes in each of the lots. The inconsistency in the results mentioned above may have been caused by variation in amounts of grape skins during the alcoholic fermentation with the accompanying effect on fermentation temperature, sulfur dioxide concentration,. pH after pressing, and concentration of nutrients (55, 56). 

Detection of Malo-Lactic Fermentation. It is imperative that the winemaker, to control malo-lactic fermentation, has a satisfactory method for its detection. Disappearance of malic acid is the indication of the fermentation, but the formation of lactic acid is not sufficient evidence since it might also be formed by yeast and by bacteria from other carbohydrate sources. The rate of conversion of malic acid is expected to reflect bacterial metabolism and growth. In New York State wines, Rice and Mattick (41) showed bacterial growth (as measured by viable count) to be more or less exponential to 106-107 cells/ml, preceding disappearance of malic acid. The rate of loss of malic acid is probably also exponential. Malic acid seems to disappear so slowly that its loss is not detected until a bacterial population of about 106-107 cells/ml is reached then it seems to disappear so rapidly that its complete loss is detected within a few days (41). Rice and Mattick (41) also showed a slight increase in bacterial population for a few days following this. 

Tyj"alo—lactic fermentation can be defined as the bacterial conversion of L-malic acid to L-lactic acid and carbon dioxide during storage of new wine. Malic acid is dicarboxylic, but lactic acid is monocarboxylic therefore, the net result of malo-lactic fermentation in wine, aside from the production of carbon dioxide, is a loss in total acidity. In commercial practice, this fermentation is not well understood, and better methods of controlling it are sought. 

Pilone, G. J., Energetics and Control of Malo-Lactic Fermentation, Doc-... 

Malo-Lacttc Starter Culture. This must be monitored with great care and precision. Most California wineries don t use Leuconostoc starter cultures for malo-lactic fermentations because the organisms are generally so unpredictable and difficult to control. Where used, in the cooler coastal areas, the results are worth the effort, but it must be stressed that this is not for amateurs. Precise control is absolutely essential. See Pilone and Kunkee (10), Tchelistcheff et al. (II), and earlier papers by Kunkee. 

The growth of malo-lactic bacteria in wines is favored by moderate temperatures, low acidity, very low levels of S02, and the presence of small amounts of sugar undergoing fermentation by yeast. It is frequently possible to inoculate a wine with a pure culture of a desirable strain of bacteria and obtain the malo-lactic fermentation under controlled conditions. The pure-culture multiplication of the selected strain of bacteria is difficult, however. It is also difficult to control the time of the malo-lactic fermentation—sometimes it occurs when not wanted, and at other times will not go when very much desired. For the home winemaker it is probably most satisfactory to accept the malo-lactic fermentation if it occurs immediately following the alcoholic fermentation. The wines should then be siphoned away from deposits, stored in completely filled containers at cool temperatures, and have added to them about 50 ppm S02. If the malo-lactic fermentation does not take place spontaneously and the wine is reasonably tart, the above described regime of preservation will likely prevent its occurrence. When the malo-lactic transformation takes place in wines in bottles, the results are nearly always bad. The wine becomes slightly carbonated, and the spoiled sauerkraut flavors are emphasized. 

Henick-Kling, T. (1995). Control of malo-lactic fermentation in wine Energetics, flavour modification and methods of starter culture preparation. J. Appl. Bacteriol. 79, 29S-37S. Imazio, S., Labra, M., Grassi, F., Scienza, A., and Failla, O. (2006). Chloroplast microsatellites to investigate the origin of grapevine. Genet. Resour. Crop Evol. 53,1003-1011. 

Prior to 1960, few made any attempts to control the malo-lactic fermentation in red wines. Ingraham et al. (19) showed that there were at least five types of lactic acid bacteria capable of decomposing malic acid in California wines. Webb and Ingraham (20) showed that the malo-lactic fermentation could be induced in the winery. Prior to that time, most malo-lactic fermentations occurred spontaneously from the inoculum normally present in the vats. 

Henick-Kling, T. 1995. Control of malo-lactic fermentation in wine Energetics, flavour modification and methods of starter culture preparation. J. Appl. Bacterial Symp. Supp. 79, 29S-37S. 

Crapisi, A., Spettoli, P., Nuti, M., and Zamorani, A. (1987) Comparative traits of Lactobacillus brevis, Lact. JrucUvorans and Leuconostoc oenos immobilized cells for the control of malo-lactic fermentation in wine. 

Kunkee, R.E. 1967a. Control of malo-lactic fermentation induced by Leuconostoc citrovorum. Am. J. Enol. Vitic. 18 71-77. 

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