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24 APRIL 1, 2015 GOOD FRUIT GROWER www.goodfruit.com Defi cit irrigation enhances color and fruitiness of wines. by Melissa Hansen R egulated deficit irrigation strategies can improve fruit quality by producing smaller berries, but does it affect the chemical and sensory properties of the wine? Washington State University research- ers found that the moderate regulated defi cit irrigation strategies generally followed by wine grape growers and more severe defi cit irrigation both positively impact the fruity aroma components of red wine. Wines from the more severe irrigation regimes also had the highest color saturation. Because viticultural practices can impact winemaking and wine quality, wine analysis is an important compo- nent of grape research conducted by WSU. Dr. Markus Keller and enologist Dr. James Harbertson recently con- ducted a regulated defi cit irrigation project on Cabernet Sauvignon wine grapes. Graduate student Dr. Luis Federico Casassa, under the guidance of Harbertson, conducted the wine sensory evaluation portion of the defi cit irrigation study. Though Casassa is now at the Wine Research Center of the National Institute of Agronomic Technology in Mendoza, Argentina, he received his PhD in Food Science in 2013. Wines made from grapes produced under regulated defi cit irrigation practices have been chemically evaluated in the past, but little research has been done on the sen- sory properties of such wines. Casassa shared highlights of his research during the annual meeting of the Washington Association of Wine Grape Growers. The wine sensory research was conducted from 2008 to 2013 on wines made from grapes from four irrigation regimes: 100 percent evapotranspiration (ET) from fruit set to harvest; 60 to 70 percent ET fruit set to harvest (industry standard); 25 percent ET fruit set to harvest; and 25 percent ET fruit set to veraison, then 100 percent ET veraison to harvest. Some of the berry and wine chemical differences under the irrigation regimes related to smaller berries from some of the most severe treatments. Small berries have a higher proportion of skin and seed derived compounds, such as anthocyanins, which play a role in wine color, and tan- nins, which give wines bitterness and astringency. Casassa found the highest levels of tannins and antho- cyanins in the 25 percent ET from fruit set to harvest irri- gation regime. In general, tannins from seeds contributed more to wines than tannins from skins, he said, and noted that tannins from seeds seem to be more diffi cult to retain in the wine matrix because they may undergo interactions with other components, such as polysaccharides, that can "sequester" them and avoid tannin extraction. Aromas and color Casassa was interested in learning if irrigation treat- ments had an effect on the volatile and aromatic com- pounds of wine. To measure sensory aspects, Casassa used trained panelists to evaluate the wines for taste, smell, and mouth-feel. He found an increase in wine anthocyanins, color sat- uration, bitterness, and astringency ratings in the wines from the 25 percent ET all season compared to other ET regimes, but less consistent effects on aroma. Yields from the 25 percent ET treatment were 30 to 70 percent lower than in the 100 percent ET. He also observed more color saturation in wines from the industry standard of 70 percent ET and the early defi - cit (25 percent ET from fruit set to veraison/100 percent ET to harvest). The two treatments also showed a reduced effect on astringency and bitterness. Both the early defi cit (25 ET/100 ET) and industry stan- dard of 70 ET enhanced red and black berry aromas in the wine. "The results suggest that moderate RDI protocols such as the 70 percent ET and 25/100 percent ET positively impact the fruity component of wine aroma," he said. "The more severe RDI protocols, like the 25 percent ET all season, increased perceived color saturation, astrin- gency, and bitterness, which could be useful for blending purposes." Casassa added that the 25/100 percent ET would be an advisable protocol to follow in Washington State if water supply becomes limited and growers need to manage water more effi ciently. • Irrigation effects on wine Ste. Michelle Wine Estates varied water amounts at different timings in an ultra-premium Cabernet Sauvignon block at their Cold Creek Vineyard. The project investigated the physiological and viticultural effects on the vines and also analyzed wine chemistry and sensory differences of wines made from the dif- ferent treatments. (See "Irrigation effects on wine.") The project included two trials cover- ing 2008 to 2010 and 2011 to 2014. Luckily for researchers, each trial included warm, cool, and average seasons, which allowed the same irrigation treatments to be studied under different conditions. Cold Creek Vineyard was planted in 1981, with a vine spacing of seven-by-ten feet in a north-south row orientation. Vines are spur-pruned and trained to a loose verti- cal shoot positioned system. In the fi rst trial, from 2008 to 2010, irrigation treatments were: —70 percent ET from fruit set to har- vest (industry standard) —35 percent ET from fruit set to veraison, 70 percent ET from veraison to harvest —70 percent ET from fruit set to veraison, 35 percent ET from veraison to harvest —35 percent ET from fruit set to harvest PHOTOS COURTESY MARKUS KELLER A side benefit of regulated deficit irrigation is weed control. Notice the abundance of weeds in the left photo (100 percent ET) compared to the lack of weeds in the 25 percent ET vines on the right. Defi cit irrigation guidelines G e n e r a l g u i d e l i n e s to follow when applying regulated defi cit irrigation regimes to wine grapes: —Avoid early season stress, which negatively impacts fruit set (this year's crop) and bud fruitfulness (next year's crop). —Avoid giving excess water in mid-season, which results in larger berries and a bigger canopy. —Avoid late season stress, which shrivels and dehydrates berries and reduces tonnage. If applying RDI to red wine grape varieties, do it early—before veraison. Don't wait for post-veraison or you will have no benefi - cial effect, says Dr. Markus Keller, Washington State University horticulturist. COURTESY LUIS FEDERICO CASASSA Washington State University researcher Dr. Luis Federico Casassa found that moderate RDI protocols such as the 70 percent ET and 25/100 percent ET positively impact the fruity component of wine aroma. ONLINE Learn more about evapotranspiration and irrigation scheduling at: www.wine.wsu.edu, www.irrigation.wsu.edu, or www.weather.wsu.edu