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70 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 A n underperforming block of young Zinfandel vines with viral symptoms was selected for study. The block is located in the Dry Creek Valley of Sonoma County, Calif., and underwent a thinning experiment in 2013. The crop on treatment vines was lag- phase thinned by 20% (removal of two to three clusters per vine), approximately 45 days after 50% bloom. Three vine rows were not thinned to act as a control, and they were allowed to progress until 95% véraison, when a green drop pass was made (Aug. 29). Berry samples from thinned vines showed more rapid progress through véraison , an increased rate in sugar accu- mulation and were ready for harvest three weeks earlier. Eighteen-day micro- fermentations produced higher quantity and quality of extractable tannins. Com- mercial-scale applications of the tech- nique appear to have led to the highest quality yet from the block. Background Planted in 2003 with 110R rootstock and budded in 2004, Lytton Estate Block X has been a consistent under-performer since it first bore fruit for Ridge Vineyards out- side Healdsburg, Calif. The 6.78-acre block is planted to head-trained, spur- pruned Zinfandel in Arbuckle series gravelly clay loam with 6 x 8 feet spacing (vine x tractor row). In the seven vintages prior to 2013, the block had never been selected for a first wine, and one harvest was sold as bulk wine. During this same period, the aver- age yield from Lytton Estate Block X was 3.2 tons per acre. Adjacent and neighbor- ing blocks are consistent high-quality parcels, which makes the lack of quality wine from Lytton Estate Block X that much more frustrating. Lag-phase fruit thinning at approxi- mately 45 days post-bloom showed prom- ise in limited trials during the 2012 vintage, in other varieties. One concern was that lag-phase thinning can increase berry weight on remaining clusters and increase or compensate for the adjusted crop. 3 METHODS Planning A vine uniformity study was conducted with Fruition Sciences in mid-April 2013 (Figure 1). Using their trunk circumference measurement analysis, representative areas for a three-row "treatment" section and three-row "control" were chosen for inten- sive berry sampling. Once the target areas were established, representative vines for sap flow sites were chosen and sensors installed. Harvest would occur at the sole discretion of the winemaker, when flavors were ripe and not based on predetermined chemical analysis. Cluster thinning A thinning pass began July 5 to the entire block, except the selected vine rows that would serve as a control (Figure 2). Both three-row areas would serve as represen- tative samples to check against each other in both micro-fermentation (approxi- mately 1 gallon) and 1-ton production fer- mentations. Two clusters were removed from vines with low to medium vigor, and three clusters were removed from more vigor- ous vines. No spatial preference was made, though areas with higher levels of clumping were targeted as were weak shoots. On Aug. 29, the control vines were thinned. Crew members were given W I N E G r o W I N G Will Thomas, Nicolas Brunier and David Gates —Ridge Vineyards, Lytton Springs, Calif., Matthew Revelette and James Kennedy— California State University, Fresno, Thibaut Scholasch, Fruition Sciences BY Effect of lag phase thinning on Z infandel Dry CrEEk VallEy Table I—Crush Informa on Treatment Control Date 9/19/13 10/9/13 Days Post Bloom 125 145 Brix 25.3 24.1 pH 3.93 4.14 TA (g/L) 6.00 3.94 Malate (g/L) 4.724 3.631 Glu+Fru (g/L) 248 225 Final Alcohol 14.0% 12.5% Tons/Acre 2.9 3.2 Figure 1. Normalized trunk circumference contours, with sap flow locations. red = low vigor, yellow = medium vigor, blue = high vigor, values correlate to color regions.