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Application Notes for Malolactic Bacteria
Strain of Bacteria Different strains of Oenococcus oeni have different fermentation characteristics and different abilities to survive the extreme conditions of wine. The characteristics and survivability are determined by the strain’s natural capabilities and the skill used in preparing the cultures to adapt. Chr. Hansen is the world’s leader in bacteria preparations for food cultures, with a wide-ranging strain bank and extensive expertise. The Viniflora strains were selected and adapted specifically to meet the varied wine parameters and the high standards of winemakers. Wine Parameters SO 2 , pH, alcohol and temperature are the key wine parameters to consider for successful malolactic fermentations. Any one of these parameters outside the bacteria’s limitations can slow down or inhibit the fermentation. It is important to remember that these parameters all work in concert with one another and together have a synergistic effect on the bacteria. Exceeding the limitations for one parameter, if others are in line, may be less restrictive than three or four parameters that are high but within the limitations for the strain. SO 2 Be aware of the toxic effect of SO 2 on malolactic bacteria and keep the addition to a minimum. In general, lower is better, with the maximum TSO 2 at 30-70 ppm depending on the strain of bacteria and the type of wine (see chart on page 16). Some strains of yeast (especially Saccharomyces bayanus ) produce high levels of SO 2 during alcoholic fermentation. Choosing an ML-friendly strain of yeast, which produces minimal amounts of SO 2 , will help to assure the success of your malolactic fermentation.
The rate of the malolactic fermentation, and ultimately, the success of the fermentation, are dependant on several key factors — the level of inoculation, the strain of bacteria used and the parameters of the wine. Level of Inoculation – The Magic Number It is frequently observed that efficient malolactic fermentations require a minimum cell density of approximately 10 6 CFU/ml… one million cells per milliliter — the magic number . Malic acid conversion has also been found to be proportional to cell density; so the more cells above one million per milliliter, the faster the malolactic fermentation will progress. This means that a pouch of bacteria used to inoculate 660 gallons must contain at least 2.5x10 12 viable cells in order to ensure an inoculation level of 10 6 CFU/ml, and all of those cells must survive inoculation into the wine. Not all commercial preparations contain this level of viable cells, nor do all manufacturers prepare the cells to survive the inoculation. Chr. Hansen not only checks its Viniflora cultures to assure that their cell numbers exceed these levels, but also checks the cell’s ability to survive inoculation and convert malic acid. Stretching the Cultures Stretching the cultures by inoculating volumes of wine greater than what is recommended is not always prudent. Stretching means that the inoculation rates of the Oenococcus oeni may fall below 10 6 CFU/ml and that a malolactic fermentation with the desirable bacteria may not start until cells go through sufficient generations. Oenococcus oeni is a slow- growing organism and can be outcompeted by other, undesirable bacteria ( Lactobacillus, Pediococcus , etc.). Ultimately the quality of the wine can be affected, and at the very least the fermentation will be drawn out by days, weeks, or possibly months, tying up tank space, requiring ongoing monitoring and enduring unnecessary risk of oxidation and spoilage.
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