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WINEMAKING valid camps depending on their terroirs and goals: the Green Juice Club (30 ppm at the crusher for healthy fruit) and the Brown Juice Club (nothing at the crusher). Bisulfite also binds to aldehydes, prin- cipally acetaldehyde, which is the penulti- mate enzymatic step in fermentation just prior to its ethanol endpoint. As a result, all sulfur dioxide added at the crusher and created by yeasts during fermentation is bound; none is free at the end of fermenta- tion. In fact, the more you add, the more you create an aldehyde pool, necessitat- ing increased addition later. To obtain 25 ppm free SO2 post-fermentation, Green Juice Club members typically add 70 ppm, whereas Brown Juice Club members need only add 50 ppm. In addition to aldehyde binding, bisulfite will observably bleach monomeric pig- ment. Though terrifying, this is a reversible reaction that actually stabilizes red color by maintaining a pool of monomeric pig- ment that is restored to the wine as it ages and the pigments polymerize. Pigment-bound forms differ from the aldehyde bisulfite complex (ABC) in that also combines in red wines with unpo- lymerized pigments, rendering them col- orless. Addition of SO2 to young red wine pH 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 % SO2 7.5 6.1 4.9 3.9 3.1 2.5 2.0 1.6 1.3 1.0 0.8 0.6 (m) % HSO3 92.5 93.9 95.1 96.1 96.8 97.5 98.0 98.4 98.7 98.9 99.1 99.2 Distribution of Free SO2 % SO3 -2 .009 .012 .015 .019 .024 .030 .038 .048 .061 .077 .097 they are in rapid equilibrium with free SO2 , and although they are included in FSO2 analysis as true free SO2, this is not actually the case. While these forms also inhibit malolactic fermentation as if they were free, they do not inhibit oxidative conversion by acetobacter of ethanol to acetic acid.5 teria in red wine is entirely dependent on reductive strength. at Various pHs Free SO2 11 ppm 13 ppm 16 ppm 21 ppm 26 ppm 32 ppm 40 ppm 50 ppm 63 ppm 79 ppm 99 ppm to Obtain 0.8 ppm Molecular SO2 0.122 125 ppm from wine through its reaction with oxy- gen, producing sulfuric acid (H2 Sulfite (SO3 Suppression of vinegar bac- shown above. Unfortunately, this does not directly protect wine from oxygen. Because it dissociates at pH 6.9, sulfite is present in very small amounts at wine pH (see table.) Its concentration, however, varies tenfold—from 0.12% at pH 4.0 down to 0.012% at pH 3.0. As a result, 2-) slowly depletes FSO2 SO4 ) as 58 Wines & Vines MARCH 2012