Issue link: http://winesandvines.uberflip.com/i/591609
124 WINES&VINES November 2015 WINEMAKING WINE EAST grapes and is found in especially high concentrations in Sauvignon Blanc. In wine, it can react with quinones, which can oxidize the volatile thiols, thereby depressing their aromatic impact. GSH can also preserve esters, terpenes and wine color during aging, according to multiple studies. A recent study of Sauvignon Blanc by Alexandre Pons found that skin contact of only 18 hours increased the GSH concentration in the must up to 55% more than in the initial concentration. Re- sults were highly variable between batches, but they always showed a higher glutathione concentra- tion with skin contact. The same study found the GSH concentra- tion to be highest in the cold- soaked must after only 30 minutes. After 30 minutes, the concentra- tion of GSH decreased. This phe- nomenon occurs because most GSH is found in the skins of the grape. Therefore, even if cold soak doesn't increase the volatile thiol concentration in a wine, it may help to preserve their aroma through an increase in GSH. It is advisable to conduct a cold soak under CO 2 and with the addition of SO 2 in order to deactivate poly- phenol oxidases and minimize oxidation, thereby allowing for the maximum retention of GSH, according to W.J. du Toit. Anti-oxidant additions The concentration of conjugated thiols is known to increase during the oxidation of juice, according to a study by Aurélie Roland. However, the volatile thiols in wine are easily oxidized. Polyphe- nol oxidases may cause phenols such as caftaric acid and catechins to oxidize into quinones, which can cause the rapid oxidation of thiols during fermentation. There- fore, wines made from musts that have been treated with an addi- tion of 50ppm of SO 2 are likely to have higher concentrations of aromas arising from volatile thi- ols, research from Carien Coetzee reveals. It's worth noting that adding ascorbic acid prior to fermentation may provide additional protection against oxidation, as it is a more powerful reducer of quinones than SO 2 , according to a 2014 study by Maria Nikolantonaki. Ascorbic acid additions warrant further re- search with regard to their use in the production of high-quality, thiol-driven wines, as the study by Nikolantonaki was performed in a model wine. It should be noted that ascorbic acid is unpredictable and can lead to the formation of pigments that SO 2 can't prevent. It also has been implicated in the formation of sotolon, a compound that produces a maple syrup-like aroma in prematurely aged white wines. Pressing Oxygen seems to be the arch- enemy of the volatile thiols. As mentioned previously, oxygen in- clusion during the juice stage will lead to a depression in the final concentration of GSH. Less GSH in the wine may leave thiols more vulnerable to oxidation by qui- nones. Therefore, pressing should be conducted under a reductive environment with carbon dioxide or nitrogen gas in order to pre- serve volatile thiols. With increasing pressure, one can extract more conjugated thiols in the press. However, with higher pressure, one will begin to extract more phenols, which can then oxi- dize to form quinones. The qui- nones will react with glutathione, thereby leaving the thiols more vulnerable to oxidation, according to research by Manu Maggu of New Zealand. Consequently, it's worth adding SO 2 prior to press- ing, as well as pressing in an an- aerobic environment in order to inhibit the polyphenol oxidases and maximize aromatic potential of the volatile thiols. Yeast strain Various yeast strains have been demonstrated to produce wines with increased concentrations of volatile thiols. As the origin of the volatile thiols is not fully under- stood, it is not known entirely why some yeast strains result in wines 360 E. State Parkway • Schaumburg, IL • 60173-5335 USA (847) 755-0360 • Toll-Free FAX: (800) 800-0320 International FAX: (847) 885-0996 • sales@kuriyama.com www.kuriyama.com The Kuriyama Value ™ Wine and Beverage Hoses POLYWIRE ® PLUS Suction & Discharge WSTF ™ Series Suction & Discharge T350LL Series Washdown CLEARBRAID ® Discharge FT ™ Series Suction T410LL Series Suction & Discharge Kuriyama of America, Inc. ™ SUBSCRIBE ONLINE AND SAVE! winesandvines.com/subscribe Print + Digital Magazine 12 monthly issues a year for $28 winesandvines.com/subscribe