Wines & Vines

64 WINES&VINES February 2018 GRAPEGROWING PRACTICAL WINERY & VINEYARD mas and flavors to be released into wine (see "Uptake and Release of Smoke Taint in Grape- vine"). Hydrolysis of the sugar bond can occur throughout the winemaking process including during fermentation, aging and storage. In fact, there can be a dramatic progressive re- lease of the smoky compounds. It has been shown that the level of guaiacol can increase from 4.3 µg/L in control (unsmoked) wine up to 388.3 µg/L in wines exposed to smoke ap- plications from juice stage to completion of malolactic fermentation. 18 The hydrolysis reaction has been pro- posed to be executed primarily by enzymes such as β-glucosidase, which are native to wine yeasts and wine bacteria. However, acid hydrolysis cannot be ruled out as a possible mechanism for release of the smoky phenols. Furthermore, it has been shown that upon consumption of smoke-affected wine en- zymes in human saliva can also cleave off remaining sugars, causing an unpleasant retro-nasal ash perception. 8 This explains why wines can have ashy notes, even when the unfermented grape juice did initially not show hints of an unpleasant aroma. Future prospects and possible solutions Thanks to wine research, we now know how such a taste can develop. In the future, a grape- vine variety could be bred to produce less GT enzyme. Alternately, a second sugar molecule could be added to prevent release of the smoky aroma, or yeasts not able to cleave the sugar- bound volatiles could be searched. From a practical point of view, it would be desirable to develop a process specifi- cally to remove the smoky volatiles or their sugar-bound forms from juice and wine without removing beneficial flavors and aromas. Unfortunately, many valuable fla- v o r / a r o m a c o m p o u n d s a r e c h e m i c a l l y highly similar to the smoky phenols, which is why the development of such a method would be very difficult. By means of genetic engineering, the grapevine gene responsible for production of the GT could be removed. However, con- sumers in certain areas such as Europe tend to reject genetically modified foods and beverages. Meanwhile, winegrowers and winemakers can take steps to minimize the sensory impacts of smoke exposure. Detailed advisory sheets are available online from the Department of Agriculture and Food in West- ern Australia and the Australian Wine Re- search Institute. 19 Katja Härtl is lecturer and researcher in the De- partment of Biotechnology of Natural Products at Technical University of Munich in Freising, Germany. She specializes in enzymatic activities and the availability of single and sugar-bound secondary metabolites in crop plants including the grapevine. Wilfried Schwab is professor and head of the Biotechnology of Natural Products Department at Technical University of Munich in Freising, Germany. His research interests are enzymes and secondary metabolites in plants, metabolic en- gineering and whole-cell biocatalysis of bioactive plant compounds. www.scottlab.com • info@scottlab.com Introducing the UNICO Filter • Filters product to turbidity below 1 NTU, keeping color and structure intact • Stainless steel membrane technology for lees filtration • Fully automatic system • For use on wine, cider, mead and lees Delivering a single pass solution for wine and lees The references for this article are available online at winesandvines.com/features. A second sugar molecule could be added to prevent release of the smoky aroma, or yeasts not able to cleave the sugar-bound volatiles could be searched. 707-938-1300 info@acrolon.com ®

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