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160 WINES&VINES January 2016 GRAPEGROWING WINE EAST that undergo dehydration are sus- ceptible to microbial spoilage, leading to Botrytis cinerea-derived increases in higher alcohols, and production of high amounts of other alcohols such as glycerol, arabitol and mannitol. 15 Sour rot can reduce terpenes; for example, free geraniol, nerol and linalool concentrations declined and trans- furan linalool oxide, benzyl alco- hol, 2-phenylethanol increased in one study of Riesling. 16 We chose to experiment with different harvest dates to deter- mine whether keeping a full crop with an extended harvest date might have a greater positive im- pact on wine volatile composition than to reduce the crop level. In many situations, our growers al- ready have a balanced vine (i.e., <10 Ravaz Index) and don't need to drop crop for the sake of bal- ancing the vine. The overall objec- tive for this project was to determine the impact of harvest date and crop control on the wine volatile composition of four grape cultivars—two whites (Riesling and Pinot Gris), and two reds (Cabernet Sauvignon and Caber- net Franc)—commonly produced in the Niagara Peninsula region of Ontario, Canada. Description of methods Experimental design: Two crop levels imposed at véraison, full crop (FC) and half crop (HC), as well as three harvest dates (includ- ing two harvest dates after regular harvest) were combined in a facto- rial treatment arrangement con- taining six treatment combinations. Harvest date treatments were T0 (normal commercial harvest), T1 (three weeks after T0), and T2 (three weeks after T1). Wines were produced from each treat- ment replicate using standard methods. 17 During 2011 and 2012, analysis of volatile compounds in wine samples by gas chromatog- raphy–mass spectrometry (GC- MS) was performed to determine whether differences existed be- tween the two crop levels and be- tween harvest dates. Sample preparation: Aroma analysis by GC-MS was carried out in 2011 and 2012 wines for the four grape cultivars based on Bowen & Reynolds 18 with adjust- ments. A 30ml sample was taken from each wine treatment repli- cate and kept at 4º C under N 2 inert gas until analysis. In dup- licate, 100 μL of an internal standard, prepared with 10 μL of 9 8 % 1 - d o d e c a n o l ( A l d r i c h ; Oakville, Ontario) in 10ml of 100% ethyl alcohol was poured into 10ml volumetric flasks to volume. The prepared sample was transferred into a 10ml Gerstel extraction vial. A 10 mm stir bar ( the Gerstel Twister) coated with polydimeth- ylsiloxane (PDMS; 0.5 mm film thickness) was added to the sample and stirred for one hour at 1,000g for extraction at room tempera- ture. After extraction the stir bar was removed, rinsed, dried and then placed in a 4ml amber vial at 4º C until analysis the same day. The stir bar was then inserted into an extraction glass tube inside the thermal desorption unit attached to GC-MS. GC-MS conditions and conditioning of material were iden- tical to Bowen & Reynolds. 18 Stir bars used for extraction were previ- ously conditioned before use every time to avoid any cross contamina- tion. After analysis, each stir bar was kept overnight in a solution of 80:20 acetonitrile/ methanol, al- lowed to dry and then placed at 250º C for two hours with a con- stant flow of N 2 inert gas. Calibration compounds and odor activity values: Scan analy- sis reflected more than 100 volatile compounds in wines from all cul- tivars. For calibration purposes, 30 compounds were chosen as highest in priority. Three-point calibration curves were created for each com- pound for quantification. Aromatic standards were obtained from sev- eral well-known chemical suppli- ers. Model wine was used for calibration curves and prepared using 12% (v/v) of pure anhydrous ethanol diluted in Milli-Q water and 5 g/L of tartaric acid with a pH adjusted to 3.6 with 1N NaOH. Each aroma standard was diluted first in pure anhydrous ethanol at 1,000 mg/L and kept at 4º C until analysis, then diluted at different concentrations in model wine. Calibration samples were analyzed in SIM/SCAN mode using the same conditions as described previously with use of the same internal stan- dard. Odor activity values were calculated as a ratio between each concentration obtained by calibra- tion vs. their respective thresholds obtained from literature. Descriptive sensory analysis Panel training: Both panel train- ing and descriptive analysis were consistent with practices previ- ously described for white 19 and red wines. 17 Panel training was conducted to create a set of stan- dard descriptors across all tasters. The panel consisted of 12 panel- ists (six males and six females) ages 23 to 56, and all the partici- pants were students or faculty members from the Brock Univer- sity Cool Climate Oenology and Viticulture Institute (CCOVI) with previous tasting experience. Six 60- to 90-minute training sessions were conducted weekly for each cultivar. A final list of aroma, fla- vor and basic taste descriptors was generated from the most fre- quently identified descriptors from the initial two sessions. TERPENES IN PINOT GRIS AND RIESLING Impact of harvest date (2011 and 2012) on concentration of several monoterpenes and ß-damascenone in Pinot Gris (left) and Riesling (right), where T0=normal commercial harvest, T1=three weeks after T0, and T2=three weeks after T1. Different letters within each compound indicate significant differences between harvest dates, p< 0.05. 0.50 0.40 0.30 0.20 0.10 0 Concentration in mg/L Citronellol 2011 Citronellol 2012 Damascenone 2011 Damascenone 2012 Terpinolene 2011 Terpinolene 2012 n = T0 n = T1 n = T2 1.2 1.0 0.8 0.6 0.4 0.2 0 Concentration in mg/L Linalool 2011 Linalool 2012 Geraniol 2011 Geraniol 2012 Terpineol 2011 Terpineol 2012 Terpinolene 2011 Terpinolene 2012 n = T0 n = T1 n = T2 a b b a a b b ab a b b a b b a