Effects of Variations in Berry Size and Manipulations of Fermentation Solids in Zinfandel Grapes and Wines
Daniel Postiglione,* Federico Casassa, and Jean
Dodson Peterson
*Wine and Viticulture Department – Cal Poly San Luis Obispo, 1
Grand Avenue, San Luis Obispo, CA 93047, San Luis Obispo, CA
93407 (dpostigl@calpoly.edu)
Zinfandel berries were segregated into four berry size classes: raisins (9.6% of distribution), 10 mm (18.5% of the distribution), 12 mm (30.5% of the distribution), and 14 mm (41.4% of the distribution), including unsorted berries, with all treatments made into wine. Berry surface increased linearly with berry size (R2 = 0.9912), but the solid to liquid ratio decreased with increasing berry size. With the exception of wine made from raisins (<9 mm), which had 168% more phenolics and 143% more polymeric pigments than unsorted berries, extraction patterns of anthocyanins, color, and tannins during fermentation were unaffected by berry size. We also manipulated berry size by adding must and fermentation solids to mimic the solid to liquid ratio of selected berry size classes. Saignée (at 29%) to mimic 12 mm in 14 mm berries only increased tannins by 22%. Addition of 36% must to 10 mm berries to emulate 12 mm berries diluted anthocyanins and tannins by 68% and 65%, respectively, and addition of 29% must in 12 mm berries to simulate 14 mm berries diluted anthocyanins and tannins by 55% and 70%, respectively, indicating that the initial tannin and anthocyanin content of the 10 and 12 mm berries was the limiting factor on extraction of these phenolics. Addition of 36% solids to the 12 mm berries to emulate 10 mm berries decreased anthocyanins by 36% relative to 10 mm, and increased tannins by 48%. We conclude that berry size cannot be easily compensated in Zinfandel; even though larger berries have a comparatively lower solid to liquid ratio than smaller ones, and should be amenable to compensation by saignée or by addition of extra solids, these practices seem to result only in positive effects on tannin extraction, but do not affect anthocyanin extraction
Funding Support: Research, Scholarly and Creative Activities Grant (RSCA), Cal Poly San Luis Obispo. Turley wine Cellars (Paso Robles, CA) are acknowledged for the generous donation of Zinfandel grapes for this project