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34 WINES&VINES July 2016 WINEMAKING PRACTICAL WINERY & VINEYARD T he role of malolactic fermentation (MLF) in red wines and many white wines is constantly being studied. Initially recog- nized as a way to deacidify wine, MLF was adopted because it imparted a degree of microbiological stability and enriched sensory attributes to wine. Tasting, which has become increasingly important in the evaluation of wines, clearly confirms the effect MLF has on the sensory characteristics of both red and white wines. In certain regions, winegrowing practices and increased grape maturity result in the gradual reduction of malic acid concentra- tion in the must. Nevertheless, MLF is use- ful—not necessarily for its deacidification function, but for its impact on the sensory composition of wines. In the 1970s, producers were very inter- ested in the role of yeast in winemaking. Starter cultures made from active dry yeast are easy to use and highly diverse. They have been carefully studied for their enological proper- ties, fermentation capacities and influence on taste and aroma. Success was much slower for selected wine lactic acid bacteria (LAB) starter cul- tures due to their physiology and sensitivity to environmental factors. Performance fail- ures of wine LAB starter cultures in the 1980s kept them from being widely ac- cepted for use. The selectors and producers of starter cul- tures have expanded their research efforts, and both academic enologists and winemakers are interested in tangible aspects of the microbiol- ogy of winemaking. Information disseminated in seminars and trade publications has fur- thered the practice of using malolactic starter cultures, a process that has overcome its dif- ficult beginnings and is now a beneficial pro- cess to achieve certain wine styles. Winemaking is a microbiological process involving a very complex system. The na- ture of the micro-organisms that inhabit grape must—along with the must's chemical composition and temperature—influence the parameters that affect wine quality. Yeast and bacterial populations in wine are varied and variable. During alcoholic fer- mentation, different yeast species succes- sively dominate, while others remain in the minority or disappear. The four fundamental parameters of pH, alcohol, temperature and CO 2 determine the evolution of indigenous microbial populations, which may be monitored by winemakers from the beginning to the end of alcoholic fermenta- tion. Interactions among microorganisms are key factors in fermentation, but those interac- tions are difficult to evaluate. The use of starter cultures that massively increase yeast population is a convenient and sure way to master the microbiological com- position of the system. The addition of yeasts has become a classic step in winemaking that has gotten more refined as different strains become available. Today, this step is becoming more complex with the arrival of non-Saccha- romyces yeast species. The addition of com- mercially available wine LAB is becoming more established as the available starter cultures become more reliable. Due to the efforts of technical and research centers, industrial R&D departments and end users, considerable progress has been made in the functionality of commercially available wine LAB starter cultures. The major problem to overcome was the survival and growth of the bacteria inoculated into wine, as their population must be sufficiently large to en- sure MLF. Wine LAB will not degrade L-malic acid unless they are viable, and viability is necessary for maintaining essential cell mem- brane functions. Wine is a medium not conducive to micro- bial growth because it contains relatively high levels of acid, ethanol, fatty acids, polyphe- nols and other compounds. Indigenous mi- croflora, on the other hand, are well adapted The Role of Bacteria in Wine Understanding wine lactic acid bacteria and what the future may hold By Aline Lonvaud-Funel, Ph.D.