Federico Casassa,* Sean Kuster, Michael Upton, James Nelson, and Bob Coleman
*Wine and Viticulture Department, California Polytechnic State University San Luis Obispo (Cal Poly), 1 Grand Avenue, San Luis Obispo, CA, 93407 (lcasassa@calpoly.edu)

Assyrtiko grapes (20.1 Brix, pH 3.19, titratable acidity 8.5 g/L, liquid:solid ratio 9:1) from the Paso Robles AVA of California were made into wine following traditional white wine fermentation carried out either at cold (between 15 and 17°C, average 15.8°C; WF-C) or warm fermentation temperatures (between 19 and 26°C, average 20.7°C; WF-W) or in an orange wine style, i.e. in contact with fermentation solids (skins and seeds), also at cold (SF-C) or warm temperatures (SF-W). Final alcohol levels were lower in skin-fermented (~11% ABV) than in white-fermented wines (~11.9% ABV). The redox potential oscillated between -100 and -20 mV during the first four days of skin contact time, then reached up to 100 mV at the end of skin contact time in skin-fermented wines. Conversely, white fermentations showed consistent redox potentials in the -100 to -120 mV range, and as low as -160 mV. There was more acetaldehyde in wines that fermented cold, and were generally higher (36 mg/L) than acetaldehyde levels normally found in finished red wines. Tannins and total phenolics averaged 10 and 82 mg/L in WF wines, respectively, and 308 and 885 mg/L in SK wines, respectively, and were slightly higher in wines fermented warmer. As expected, wine color was 87% higher in SF wines. Assyrtiko wines made with skin fermentation had tannin and total phenolic profiles similar to those observed in Central Coast AVA Pinot noirs, although they did not produce polymeric pigments. This is the first time, to our knowledge, that the phenolic profile of skin-fermented Assyrtiko wines, a staple variety from Santorini (Greece), has been described. This work is part of a larger project aiming at assessing the winemaking potential of emerging varieties of Mediterranean origin in the Central Coast of CA.

Funding Support: Richard Lauchland (Duas Terras Vineyards, Paso Robles, California).