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72 WINES&VINES April 2016 GRAPEGROWING both Shiraz and Carignane. The large study on Shiraz in Australia, in which severe pruning (i.e., dramatic reduction in yield) in fact de- creased or had no effect on wine color in three of four years, has already been mentioned. From their work together in California, Free- man and Kliewer concluded, "Contrary to popular belief, increasing the pruning level, hence yield, generally increased these quality parameters." In the late 1980s, a study of Cab- ernet Sauvignon in Napa Valley by Kliewer at UC Davis found that taste panels could suc- cessfully distinguish between 6.6 and 11.0 tons per acre wines in only one of two years, and could not distinguish between wines made from vines with smaller differences in yield. In addition to several studies in the 1980s already mentioned, many studies over the next two decades reported similar observa- tions. In Pinot Noir, large differences in yield (twofold) caused no differences in fruit color or pH, and cluster thinning to reduce yield about 35% had no effect on skin tannin or color in a study of Merlot in three consecutive years. Other Australian studies in hot regions reported a nil to weak relationship between yield and berry color in Shiraz and Cabernet Sauvignon vineyards. In yet another compre- hensive study of Shiraz wines produced in South Australia, John Gray and coauthors were unable to find a relationship between yield and their "wine value index" across a large sample of growers in several regions. Leading grapevine scholar Markus Keller and colleagues conducted a series of studies in Washington state that involved changing yield in various ways. In one five-year study, after reducing clusters by about 25% in Cab- ernet Sauvignon, Riesling and Chenin Blanc, Keller and colleagues found that "cluster thin- ning and its timing had little or no influence on shoot growth, leaf area, pruning weight, berry number, berry weight and fruit composition (soluble solids, titratable acidity, pH, color) in both the current and subsequent seasons." In another five-year study, reducing clusters by about 40% had no effect on fruit composition (including color) in Cabernet Sauvignon. In 2010, Keller and colleagues conducted novel experiments in which the temperature of buds was increased in order to enhance their fruitfulness and found that "although yield per shoot varied threefold among treatments, differences in fruit composition were minor." Yet the world of winegrowing has not assimilated these many experimental contradictions of HYLQ. There are a few authors who have reported positive changes in fruit or wines (such as increased fruity aroma) with increasing yield, regardless of harvest criteria. However, for fruit harvested at similar Brix, the conse- quences of yield reduction by pruning or clus- ter thinning for grapes and wine, when present, are often similar to the slightly in- creased astringency in Cabernet Sauvignon wines reported by Chapman, Matthews, and Guinard (2004). That is, changes in sensory attributes that are sometimes statistically sig- nificant but also small. In that 2004 study, wine astringency ratings were closely corre- In most cases when yields varied but fruit were harvested at the same Brix (rather than on the same date), studies have found little or no significant differences or loss of quality attributes in fruit or wine.