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GRAPEGROWING release of "reductive" or sulfur-containing compounds. If there is a desire to store dry white wines in tanks sur lie, it is recommended that the lees be stored in barrels for several months, then added back to the tank.22 Protein stability — The greater the lees contact, the lower the need for bentonite for protein stability. It is not believed that lees hydrolyze grape proteins, or that proteins are adsorbed by yeast. Rather, lees aging produces an additional mannoprotein, which adds stability. The production is increased with temperature, time and frequency of stirring. Biological stability — M. Guilloux‑ Benatier et al. have studied the liberation of amino acids and glucose during élevage of red Burgundy wine on lees.13 Their studies were done with and without the addition of exogenous b‑1,3-glucanase preparations. Their most significant finding was an increase in glucose concentration, from 43 mg/L in the control wine, to 570 mg/L in wine stored on its lees, to 910 mg/L in wine stored on its lees with added b‑1,3-glucanase. Thus, the growth of the spoilage yeast Brettanomyces in barreled wine may be stimulated by the availability of this carbon source. Bitartrate stability — Mannoproteins produced by yeast can act as crystal inhibitors. The longer the lees contact time, the greater is the likelihood of potassium bitartrate stability. Removal of mycotoxins — The volume of mycotoxins including Ochratoxin-A is less as a result of the use of lees, which can act as a fining agent to both adsorb and, in some cases electrostatically bind compounds and remove them from solution. Reductive strength — Longevity, or the ability to age, is an important quality attribute. The reductive strength of a wine is a measure of the uptake of oxygen. This is influenced by the phenol composition and lees, among other things. The reaction of a young wine with oxygen can make that wine more resistant to later oxidation. This means that young wines can consume oxygen which increases the reductive strength by increasing resistance to later oxidation. C. Smith noted that lees (and particularly suspended lees) in a young wine deplete the oxygen concentration.24 As such they can impact the degree of oxidative phenol polymerization thus increasing astringency and possibly reductive strength. Wine lees are an important tool for winemakers. They influence mouthfeel, aroma, bouquet, oxidative, physical and microbiological stability. Additional research is needed to help clarify the influence of both yeast and bacterial lees on these and other wine features. PWV This text was adapted from Enology Notes #162, available at: vtwines.info. Bibliography 1. Boivin, S., M. Feuillat, H. Alexandre and C. Charpentier. 1998 "Effect of must turbidity on cell wall porosity and macromolecule excretion of Saccharomyces cerevisiae cultivated on grape juice." Am. J. EnoI. & Vitic. 4: 325–331. 2. Charpentier, C., and M. Feuillat. 1993 "Yeast autolysis." In Wine Microbiology and Biotechnology. G.H. Fleet (ed.), pp. 225–242. Harwood Academic Publishers, Chur, Switzerland. 3. Delteil, D. 2001 "Working with lees: Key elements to wine maturation." 30th Annual Technical Issue of Aust. & NZ Grapegrower & Winemaker. 4. Delteil, D. 2002. Verbal communication. 5. Escot, S., M. Feuillat, L. Dulau and C. Charpentier. 2001 "Release of polysac- Liquid Nitrogen Dosing Systems: Key Benefits: Flushes oxygen out of bottle head space Keeps the fruit in every pour Best "locks in" FSO2 levels 800.371.3303 www.chartdosers.com Dosing The World One Drop At A Time pr actica l win ery & vin eya rd AU GU ST 20 13 79