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July 2016 WINES&VINES 41 PRACTICAL WINERY & VINEYARD WINEMAKING wine. This technique is not in commercial application, but its parameters have been studied. The advantages are a greater tol- erance toward inhibitors, the re- usability of the inoculum and an increased rate of L-malic acid deg- radation. 17 Research has been con- ducted on this process, but trials are limited to small-volume ex- periments in laboratory media. Immobilization of O. oeni was done on grape skins and stems as solid supports. 14 Mixed yeast and bacteria reac- tors also have been tried. In this scenario, the must first enters a Saccharomyces cerevisiae reactor and is then passed to an O. oeni reactor. The chemical composition of esters and other volatile com- pounds suggests the wine pro- duced in this trial has no defects and would be fruity and floral. 14 In another variation, a biore- actor sheet containing immobi- lized cells of S. cerevisiae and O. oeni was used. The sheet can be dried, stored and added to grape must. It triggers alcoholic fer- mentation and L-malic acid deg- radation, and the resulting wine has no analytical defects. 28 Unlocking more questions Because of its sensory impact, ma- lolactic fermentation is a valuable step in winemaking, even for wines with low levels of L-malic acid. Progress in the preparation of se- lected wine lactic acid bacteria starter cultures has made them reliable tools utilized by many winemakers. Their effectiveness has been improved by better strain selection and by defining protocols for their growth and preparation. These production advances have been largely accomplished by the producers of commercially available strains. The scientific un- derstanding of wine lactic acid bac- teria in general (and Oenococcus oeni in particular) has advanced considerably in terms of physiology, metabolism and genetics. The identification of malolac- tic bacteria species, the genetic typing of wine LAB strains and the genetic identification of undesir- able organisms has occurred, but improvements to wine LAB starter cultures have remained limited. The adaptation of cells to their survival and growth in wine has been attempted, but scientific re- search data are able to explain only a portion of the observations. To date, discovering the reasons definitively responsible for the enological quality of certain se- lected wine LAB strains has been more difficult than expected. Research into comparative ge- nomics and investigations into the products of gene expression have yielded limited results, but high- throughput investigative genetic methods may stimulate progress. However, although adapted to lactic acid bacteria in wine, these methods alone will probably not provide solutions. Genetic markers for quality will be identified only by estab- lishing correlations between the level of transcription of genes c o d i n g f o r p r o t e i n a n d t h e strain behaviour under enologi- cal conditions. Correlations can be significant only if analyses are carried out on extensive col- lections of wine LAB strains growing in a sufficient number of different wines. Laboratory studies on such fundamental parameters as alcohol and pH is only a first step. Fluidized bed reactors of wine LAB alone or mixed with S. cere- visiae still seem far in the future. Attaching the bacteria to supports that can be utilized in batches may be a little closer. Progress depends on close col- laboration among winemakers, producers of selected wine LAB cultures and scientists. Dr. Aline Lonvaud-Funel is a professor emeritus at the Institut des Sciences de la Vigne et du Vin Université de Bor- deaux. She is an enologist and holds a degree in biochemistry. Her first re- search was under the direction of pro- fessor Pascal Ribéreau-Gayon. While earning a Ph.D. she studied lactic acid bacteria in wine. This text and figures are reprinted from the book Malolactic Fermentation—Im- portance of Wine Lactic Acid Bacteria in Winemaking published by Lallemand. The references for this article are available online at winesandvines.com