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January 2016 WINES&VINES 159 WINE EAST GRAPEGROWING Impact of Crop Level and Harvest Date Ontario research looks at wine aroma compounds and sensory properties By Andrew G. Reynolds, Luis Hugo Moreno Luna and Fred Di Profio KEY POINTS Researchers at Brock University studied whether a full wine grape crop with a delayed harvest date (akin to appassimento) might have a greater positive impact on wine aroma than reducing crop level. Four grape varieties from a vineyard in Niagara-on-the-Lake, Ontario, were subjected to two crop level treatments (full crop and half crop) and three different harvest dates in 2011-12. Delayed harvest surpassed the effects of crop reduction for most volatile components. Crop level had little impact on the sensory properties of all four cultivars in both seasons. Delayed harvest resulted in substantial and mostly positive sensorial changes. Extended harvest was in some cases disadvantageous, however. M ore than 800 volatile compounds have been identified in wine. 1 Some of these compounds can be associated with vari- etal characteristics or are generated during fermentation, while oth- ers are considered undesirable when they occur. 2 Volatile compounds become part of the wine mix by different sources. In grape sugars, for example, fermentation releases primary metabolites ethanol and CO 2 , sec- ondary metabolites esters, acids and higher alcohols, non-volatile grape-derived pre- cursors such as monoterpenes, norisopren- oids and some thiols that are released by enzymatic action by bacteria and yeasts, and esters and diacetyl 3 from the action of malolactic bacteria. The effects of crop level reduction on berry composition are normally an increase in sugar level (Brix) and a corresponding increase of ethanol. Crop reduction may increase free and bound terpenes, 4 indi- vidual monoterpenes and norisoprenoids, 5 anthocyanins and phenols, 6 as well as in- creasing volatile acids. 7 Delay of harvest also is linked to an increase in Brix by a reduction in berry weight due to dehydra- tion processes. 8 In addition to Brix, pheno- lics 9 and aroma compounds 10 are either concentrated or new ones are produced. The drying of fruit also generates shrink- age, which modifies the shape and dimen- sion of the transported products. 11 This change or reduction of volatiles and polyphenols is not only due to concen- tration but to changes in metabolism. 12 Dehydration by controlled processes can reduce ethyl acetate and acetic acid, 13 and increase ethanol and acetaldehyde, among other compounds. 14 Wines made from de- hydrated grapes normally contain more terpenes and norisoprenoids. 8,13 Grapes CABERNET FRANC HARVEST DATE RIESLING HARVEST DATE Impact of harvest date on aroma and flavor descriptors of 2011 Riesling (above left) and 2012 Riesling (below left) and 2011 Cabernet Franc (above right) and 2012 Cabernet Franc (below right) from Pondview Estate Winery in Niagara-on-the-Lake, Ontario. Lowercase descriptors are orthonasal aroma and uppercase are ret- ronasal aroma/taste/mouthfeel. *, **, ***, ****, NS: Significant at p < 0.05, 0.01, 0.001, 0.0001, or not significant, respectively. T0=normal commercial harvest, T1=three weeks after T0, and T2=three weeks after T1.