Impact of crop level and harvest date on aroma compounds of four Vitis vinifera wine grape cultivars in Ontario, Canada

Abstract

Pinot gris, Riesling, Cabernet Franc and Cabernet Sauvignon from a vineyard in Niagara-on-the-Lake, Ontario (Canada) were subjected to two crop level treatments (full crop, half crop) combined with three harvest dates [commercial harvest (T0), 3 wk after T0 (T1), 6 wk after T0 (T2)] in 2011-2012 in a randomized experiment. Wines were produced from all treatment replicates. We hypothesized that a full crop with a longer “harvest date” (≈ appassimento) might have a greater positive impact on wine aroma than reducing crop level. Analysis of wine aroma volatiles was carried out by GC-MS. Aroma compounds were quantified by calibration with analytical standards prepared at different concentrations in model wine. Delay in harvest overcame effects of crop reduction  for  almost  volatile  components.  Pinot  Gris  and  Riesling  benefitted  with  increases  in  varietal  aromas e.g. monoterpenes (linalool, geraniol, citronellol) and increases in esters, aldehydes, alcohols, and norisoprenoids. Reduced concentrations with delayed harvest for volatile acids and grassy-green odour compounds (e.g. 1-hexanol, hexanoic acid) in wines were also evident and beneficial for odour quality. Increases in ethanol were related to increased berry and must sugars, but higher alcohols did not increase with harvest date. Extended harvest was in some cases disadvantageous, particularly for T2 treatments, due to production of compounds like benzaldehyde, diethyl acetal, or higher concentrations of higher alcohols e.g. isoamyl alcohol and nonanol in T2 treatments, which could be linked to pre-harvest spoilage.