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p r a c t i c a l w i n e r y & v i n e ya r d J U ly 2 0 1 4 71 W I N E G r o W I N G similar criteria as during the July thin- ning pass, being instructed to remove up to three clusters per vine, including short shoots and green clusters. Measurements Sap-flow sensors were installed in mid- May, and weekly pre-dawn water poten- tial (PDWP) readings started in mid-June. Two irrigations of 12 gallons per vine were triggered — one on July 27, the sec- ond on Aug. 23. Until harvest was immi- nent, the PDWP never went below -0.65 mPa (-6.5 bar). Three hundred berry samples were taken in duplicate from the treatment and control sampling areas. One sample was sent to ETS Laboratories to analyze Brix, pH, TA, malate, glucose, fructose, sugar per berry and berry weight. A duplicate sample would have individual berry weights recorded prior to delivery to Cali- fornia State University, Fresno (CSU Fresno), for tannin analysis. Based on field observations, berry volume and densities were recorded after the third sampling. Tannin analysis The tannin analysis method was centered on a recently developed HPLC method by CSU Fresno. The technique measures tan- nin concentration and tannin "sticki- ness." 1 This measurement gives insight into how strongly the tannins will stick to hydrophobic surfaces and has been shown to be effected by tannin structure as opposed to concentration. Current research suggests that the mechanism of astringency is based in part on hydrophobic interaction (and subsequent precipitation) of salivary pro- teins. This "activity assay" does not com- pletely describe mouthfeel quality. As has been previously shown in other stud- ies, tannin concentration and matrix composition are also important. In January 2013, after the traditional assemblage tasting, Ridge Vineyards submitted 2012 vintage samples for pro- cessing through the above analysis. After seeing how closely the activity assay matched internal tasting notes and decisions (both in positive and neg- a t i v e a t t r i b u t e s ) R i d g e Vi n e y a rd s approached CSU Fresno about collabo- rating on this project. RESulTS Before bloom, cluster cou nts were recorded throughout the block. Average clusters per vine was 16.7; after thinning, the treatment area averaged 14.8 clusters per vine. Berry samples were taken every nine to 14 days, starting July 11 (one week after the thinning pass occurred). Berry weights from the samples can be seen in Figure 3. After the fourth sample, the berry weights are statistically signifi- cantly different, and the slope of the berry weight is steeper in the treatment vines prior to that point. Berry weight divergence in the two regimes agrees with the findings of B.M. Freeman and W.M. Kliewer. 3 Peaks in berry weight are 21 days apart; the treat- ment and control were picked 20 days apart. Onset of véraison was also more rapid in treatment vines. On Aug. 14 (43 days after the thinning pass), samples taken from treatment vines showed 72% véraison, while control vines showed only 54%. Brix increased more rapidly and peaked higher in the treatment vines, compared to the control (Figure 4). pH increases match the Brix trends. Glucose and fructose curves diverged early after the thinning pass, ultimately peaking higher and leading to wines with notably different crush statistics and alcohol lev- els (Table I). Sugar per berry increase was faster in the treatment vines; glucose/fructose levels not only increased faster in the treatment vines, but the peak was 23 grams higher per liter. Treatment vines also appeared to show an increase in anthocyanin synthesis. This increased rate of anthocyanin synthesis and syn- chronized peaking of sugar loading in the treatment vines ultimately led to fruit that was commercially ripe more quickly. This coupling effect is more common in cooler climates 5 and can be uncoupled in the same location in warmer vintages. 4 The wines were notably different (see Table II). Treatment vines had a greater tannin extractability (increase of 354 mg/L in treatment wines). Wine from treatment vines also displayed more strongly binding tannins, whereas con- trol wines showed more weakly binding tannins (40% decrease in binding affin- ity) — and by extension, less astringency. Sap flow profiles and PDWP values were notably different for each thinning regime (Figure 6). After the thinning pass, sap flow in treatment vines decreased, though the PDWP and physi- cal appearance painted a more moderate stress scenario. Conversely, the control vines exhibited a more erratic water-use pattern, defined by high peaks after water input and less ability to decrease water use during heat events. Take home Untimely rain came through the North Coast of California on Sept. 21, depositing 0.3 inches on Lytton Estate Block X. Fortunately, the entire block (except for the three control vine rows) was har- vested two days earlier, 125 days post- Table II—Wine Data Treatment Control Percent Skin Tannin 84% 74% Tannin Concentra on (mg/L) 2,780 2,426 Binding Enthalpy (-J/mol) 5,462 3,230 Figure 2. trunk circumference contours and trial areas overlaid on 2013 véraison enhanced vegetation index (evI). 0.2 to 1.7 1.4 to 0.2 0.2 to 1.7