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w i inneeGM A K IN GG w R O WIN of spoilage bacteria and yeast that can adversely affect a wine's flavor. The most common of these are Acetobacter, L a c t o b a c i l l u s , Pe d i o c o c c u s , a n d Brettanomyces. All of these are sensitive to some degree to sulfur dioxide but the best results come from a combination of sulfur dioxide and good cellar practices. Acetobacter is also known as acetic acid or vinegar bacteria. As the name implies, it can grow in wine and produce vinegar (acetic acid). Acetobacter can only develop in the presence of oxygen and often becomes a problem in wines that are being aged in un-topped containers. It can be controlled with a combination of sulfur dioxide and keeping tanks and barrels topped and full after fermentation. Lactobacillus and Pediococcus are both forms of undesirable malolactic bacteria. Lactobacillus typically grows in high pH red wines that have a stuck fermentation. It grows on the sugar present from the incomplete alcoholic fermentation and produces large quantities of acetic acid. Because it usually grows in high pH musts (greater than 3.75), sulfur dioxide is less effective. The best treatment is prevention, adding acid to a high pH must, and maintaining a healthy fermentation that completes to dryness. If Lactobacillus has already become established, lysozyme (an antimicrobial enzyme that is effective at high pH), can be added to control growth. Pediococcus produces an off-aroma that is described as "vegetal" or "dirty socks" and often comes from cooperage that has not been kept clean. Like all spoilage microbes, it can be prevented by a combination of proper sanitation of winery equipment and cooperage, adding pure inoculums of yeast and malolactic bacteria for fermentation, and the addition of sulfur dioxide. Brettanomyces is yeast that can grow in wine without the presence of oxygen or sugar. It usually shows up in high pH red wines while they are being aged and it produces an aroma that is described as "barnyard" or "horse sweat." Brettanomyces grows very slowly and some winemakers feel that a small amount of its aroma can add complexity to a wine. However, too much of this character can be seen as a flaw and most winemakers avoid it. Sulfur dioxide usually does not kill Brettanomyces but prevents it from growing. As a wine ages, the level of free SO2 diminishes, and a wine that has been adjusted with sulfur dioxide prior to being placed in barrels may require supplementary additions as it is being aged to prevent Brettanomyces from developing. When to add sulfur dioxide The flavor of white wines always benefits from the preservative nature of sulfur dioxide. The timing of the addition, whether it is added before or after alcoholic fermentation, has a huge affect on a wine's ultimate character. If sulfur dioxide is added prior to alcoholic fermentation, the enzyme polyphenol oxidase is inhibited and less oxidative browning of the juice occurs. This helps to preserve the fruity and floral aromas found in the juice. The presence of sulfur dioxide will also inhibit malolactic bacteria and help to prevent malolactic fermentation (MLF) from occurring, leaving more of the natural acidity in the final wine. This method is preferred for fruit-forward wines with crisp acidity that will not receive a great deal of barrel ageing. If sulfur dioxide is not added prior to alcoholic fermentation, more oxidative browning will occur and, within a few days of pressing, the juice will take on a Your source for informative technical books. ORDER TODAY! www.PracticalWinery.com and click BOOKSHELF pr actica l win ery & vin eya r d JANUARY 20 14 57