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Application Notes for Malolactic Bacteria
Wine Parameters SO 2 , alcohol, pH, 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 30-40 ppm depending on the strain of bacteria and the type of wine (see chart on page 10). Some strains of yeast (especially Saccharomyces bayanus) produce high levels of SO 2 during alcoholic fermentation. Alcohol High levels of alcohol have an inhibitory effect on bacteria. In general, Viniflora strains can handle up to 14% alcohol, and the CH16 strain is especially selected for high alcohol wines of up to 16% alcohol. pH Low pH levels create challenging conditions for malolactic fermentations. Most Viniflora strains can handle pH levels down to 3.2. The CH35 and CH11 strains were selected to handle lower pH levels, and under certain conditions can go down to 3.0. High pH can be a challenge as well in that both desirable and undesirable bacteria find it easier to thrive. High pH values usually dictate the need for a strong inoculation of Oenococcus oeni to outcompete undesirable bacteria. Temperature The optimal temperature for malolactic fermentation is 17 - 22 °C / 63 - 72 °F, with a maximum temperature of around 25 °C / 77 °F. Temperatures below 10 °C / 50 °F will slow the metabolism of malolactic bacteria to the point that fermentation is significantly delayed. Low temperatures in the wine do not necessarily kill the cells under most conditions, but will make them dormant. In most cases, if all other parameters are good, the fermentation can be restarted by heating the wine to optimal temperatures. Temperatures above 25 °C / 77 °F can kill Oenococcus oeni and should be avoided.
The rate of malolactic fermentation, and ultimately, the success of the fermentation, is dependent on several key factors:
• The strain of bacteria • The level of inoculation • The parameters of the wine
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. Novonesis is the world 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 parameters of wine, and the high standards of winemakers. Level of Inoculation – The Magic Number 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 106 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. Novonesis 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.
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