Diagnostic Key Prevention of Post-Fermentation Off-Character Production
Prevention of Post-Fermentation Off-Character Production
Prevention of Bacterial Spoilage
Traditional wine making practices were designed to prevent bacterial spoilage in wine. When the pH of your wine is kept at or below 3.8 few bacteria will grow in it. Only Oenococcus routinely grows at pH 3.6 and below. The addition of SO2 at the crusher and periodically during the wine making process prevents the growth of most bacteria while having a lesser affect on the more resistant yeast. The absence of oxygen during fermentation, aging and bottling prevents the growth of acetic acid bacteria that can turn your wine to vinegar. Traditional fining agents, such as gelatin, isinglass, egg whites, skim milk (casein), bentonite, and activated charcoal can reduce the numbers of bacteria and remove nutrients that the bacteria can grow on.
New techniques are also available to reduce or prevent the growth of bacteria in wine. The addition of lysozyme prevents the growth of the gram positive lactic acid bacteria. Addition of dimethyldicarbonate (DMDC or Velcorin) is used to kill microbes usually at the bottling stage. Filtration of wine is another successful method for the prevention of bacterial growth in finished wine.
Prevention of Brettanomyces Spoilage and Management of Infection
Once you have Brettanomyces in your winery it can be nearly impossible to eradicate. Good sanitation practices are the primary route for prevention of Brettanomyces spoilage. Cleaning will remove biofilms and Brettanomyces from surfaces in the winery. Sanitizing surfaces will keep the numbers of Brettanomyces in the winery low. Prompt cleaning of equipment and spills prevents build up of populations and spread of Brettanomyces by insect vectors. Sanitizing barrels is a difficult but important aspect of any sanitation program. Wood is impossible to completely remove contamination from but there are methods that will penetrate the pores in the wood to some extent. These methods take advantage of gas as a sanitizer such as ozone or chlorine dioxide. Both of these methods can be expensive and dangerous to use and should only be done by trained personnel.
Secondary to this are methods to prevent Brettanomyces in the finished product. Fining and filtering are the primary methods here. While fining serves to both remove Brettanomyces from the wine and to remove nutrients that Brettanomyces can grow on, it does not prevent the growth of all Brettanomyces. Proper filtration with a 0.45 µm nominal filtration system prior to bottling will remove all Brettanomyces from the wine but if spoilage has already occurred, filtration will be of little use.
Other useful methods to control and prevent Brettanomyces spoilage include chemicals to kill or prevent Brettanomycesgrowth, control of nutrient availability, temperature control, and careful monitoring. Sulfur dioxide will slow down growth and keep numbers lower. All of the Brettanomyces strains that have been tested are sensitive to dimethyldicarbonate (DMDC, Velcorin) which can be used at bottling. Storage of wines at low temperature will slow growth of any Brettanomyces that might be present. Finally monitoring wine for Brettanomyces contamination makes certain that actions can be taken early to control any potential problems.