From: Bruce Zoecklein
Subject: Calcium mucate formed from rot-degraded fruit, stressed fermentations, immature skin and/ or seed phenols
Calcium mucate. As indicated in the latest news journal, mucic acid can be formed in rot degraded grapes, resulting in the formation of calcium mucate a crystalline precipitate. Rot causes the enzymatic oxidation of galacturonic acid (the structural backbone of pectin) to mucic acid. In the presence of calcium this may form the insoluble salt calcium mucate.
If you are processing rot-degraded fruit and have used calcium sprays in the vineyard your wines are at rick of forming this precipitate shortly after bottling. This is another good reason for having a fruit sorting table and carefully culling out rot. If you are unable to remove almost all of the rot , I would suggest that we examine your wines for calcium mucate prior to bottling.
Stressed fermentations The elevated fermentable N levels as a result of the wet season have, in many cases, been off-set by fruit rot. Depletion of N and residues from some late season sprays can either inhibit fermentation or cause off aroma/flavors. A review of the factors influencing fermentations is posted on my web site at www.fst.vt.edu/Zoecklein
Immature phenols. If rot degradation requires that you bring in reds with slightly immature skin or seed tannins, process to encourage maximum polymerization: Keep the sulfur dioxide low, even if you have some rot in the tank. If the SO2 level is too high it will simply prevent phenols from binding together. Sulfur dioxide in juice have little real anti -microbiological effect except at very high levels. Ferment at relatively warm temperatures ( liquid up to 86 F or 30 C). This will add depth (as a result of increased extraction) and will increase the rate of polymerization.
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