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WINERY Excess hydrogen sulfide is typi- cally produced when yeast lack ade- quate nitrogen or vitamins. If the aroma persists after the fermenta- tion is completed, some of the sul- fur compounds can be removed. Table 2 includes a list of the offend- ing sulfur compounds found in wine, the concentration at which most people can perceive them, and a description of the aroma. When added to wine in very small quantities, copper sulfate forms an insoluble precipitate (cop- per sulfide) that can be left behind after racking. The addition should be less than 0.5 mg/L, which is the maximum residual allowed accord- ing to federal laws. The measurement of copper is best left to commercial laboratories because of the equipment required. Although a great way to remove sulfur, copper can also oxidize your wine, so it is important to control its use. Traces of brown/black pre- cipitate will form but are not always Description observed. Negatively charged pro- teins may react with copper and so occasionally it will be necessary to add further copper to remove the sulfur compounds. The reaction between copper and H2S is over quickly and a change can be per- ceived after a few hours. Other sulfur-derived off-aromas are thiols and alkyl sulfides. Thiols have a free sulfhydryl group (-SH) and can be bound by copper and removed, but alkyl sulfides (-CH2-S- CH2-) have alkane groups attached to sulfur that hinder copper's ability to bind sulfur. The most prominent alkyl sulfide is dimethyl sulfide, which is a very disagreeable aroma, reminiscent of rotten cabbage or the seaside at low tide. In model solutions it is possible to use sulfite in conjunc- tion with ascorbic acid (vitamin C) to cleave the disulfide and trap oxygen radicals, thus preventing the reformation of the disulfide so copper may be used to remove the PROBLEMS THAT CAN BE SOLVED WITH FINING Problem H2S, Thiols Polysaccharide Proteins Tannins (Excess) Catechins Browning, Stink Stinky (rotten eggs, stagnant water, onions) Haze (gelatinous masses) Haze (off white flakes) Astringent Bitter Off color, aroma FEELING STUCK? We can help avoid VA side effects. Only ConeTech can reduce the alcohol in fermenting must, without the slightest negative effect on the wine. www.conetech.com info@conetech.com ConeTech has helped countless winemakers solve this serious problem. To see how we can help you call us at (707) 577-7500. WWW.VWM-ONLINE.COM Fining Agent Copper Sulfate Enzymatic Treatment Bentonite Protein PVPP Carbon thiol. However, many winemakers report no appreciable reduction in dimethyl sulfide with this method. Yeast hulls have been promoted as a means of removing sulfur aro- mas – including dimethyl sulfide – but there is limited published evi- dence to support the claim. Aera- tion of wine is another popular way to remove hydrogen sulfide. One of the most difficult aspects of sulfur defects is there are no methods available in a typical win- ery to measure them. Gas chro- matographs must be equipped with special detectors for sulfur that only commercial laboratories can usually afford. Since the threshold of most of these compounds is very low, the best alternative detec- tor is your nose. Thus, monitor- ing your cellar for sulfur aromas is probably the most effective option short of sending samples to a com- mercial laboratory. PROBLEM-SOLVING There are many problems that can be handled with fining. Careful monitoring of your wine and char- acterizing its development during production will help in maintaining high quality. However, it is impor- tant to note that addressing vine- yard issues such as vine nutrition and site selection can help prevent some of these problems. This article is an excerpt from "A Guide to the Fining of Wine," published by WSU Extension. To download the full document, with references, visit http://cru.cahe. wsu.edu/CEPublications/em016/ em016.pdf. James F. Harbertson is an associ- ate professor and the extension enologist for Washington State University, Prosser. His research is focused on the phenolic com- pounds found in grapes and wine and their biochemical and chemi- cal changes during grape ripening, winemaking and aging. Comments? Please e-mail us at feedback@vwm-online.com. NOV - DEC 2012 VINEYARD & WINERY MANAGEMENT 85