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WineEast In the northeast, the wines often most in need of acid reduction are those most resistant to MLF. To get over this hurdle, it helps to understand what factors promote or inhibit MLF. Remember that wine, by its very nature, is endowed with anti- microbial properties, namely sulfur dioxide, low pH, alcohol and relatively limited residual nutrient levels. This challenging environ- ment inhibits the vast majority of microorganisms in the universe and, fortuitously, all known pathogens. While LAB exhibit some degree of resistance to these limiting factors, they still feel the stress from them. When MLF is desired, winemakers should take measures to accommodate the bacteria's sensitivities. Factors inhibiting MLF Sulfur dioxide: LAB are very sensitive to SO2 than 30ppm or a free SO2 . A total SO2 of more greater than 10ppm can completely inhibit MLF.2 p H: Below pH 3.1 it is very difficult to initiate MLF. Alcohol: Alcohol levels higher than 13.5% in white wines and 14% in reds have an inhibitory effect on LAB. Temperature: LAB are strongly inhibited by temperatures below 60°F (16°C). They tend to perform best in the range of 64°-70°F (18°-21°C.)3 Medium-chain fatty acids: Certain medium-chain organic fatty ac- ids can interfere with MLF. These fatty acids are produced by yeast during fermentation and can inhibit the growth of LAB. Inadequate nutrients: Through clarification and alcoholic fermen- tation (AF), many of the nutrients required by LAB are depleted. Waterloo_Nov10.qxp 8/26/10 11:36 AM Page 1 In addition to the more common inhibitors mentioned above, other potential impeding factors are residual pesticides4 and growth of the spoilage organisms Lactobacillus and Pediococcus. To my knowledge, I have never encountered inhibition due to residual pesticides, at least to the extent where it was not remedied, inadvertently, by ad- justing one or more of the other factors already discussed. Low-level treatment with carbon is cited as a solution to pesticide inhibition.5 Excessive growth of undesirable LAB, notably Lactobacillus and Pediococcus, can inhibit desirable LAB like Oenococcus oeni (a.k.a. Leuconostoc oenos) through nutrient depletion and produc- tion of bacteriocin.6 In the cellar If MLF is desired, the must should receive no more than 50ppm of SO2 SO2 at crush. Entrainment during AF will eliminate about half this , with most of the balance being bound-up with acetaldehyde and other sulfur-binding substances. No further SO2 addition should take place until MLF is complete. In addition, it might be wise to use a low-SO2 tion to ensure a low post-fermentation SO2. If pH is below 3.2, it should be adjusted upward with calcium carbonate or potassium bicarbonate before LAB inoculation. Bench trials should be used to determine the proper treatment level. In practice I prefer using KHCO3 (potassium bicarbonate) because it stabilizes faster than CaCO3 (calcium carbonate). I shoot for a pH of no less than 3.2 to better encourage the bacteria. -producing yeast for the alcoholic fermenta- Wines & Vines JUne 2012 61