Abstract Federico CasassaRobert HuffEmily Miller

Effect of Stem Additions and Microwave Extraction of Musts and Stems on Syrah, Merlot, and Cabernet Sauvignon Wines

Federico Casassa,* Robert Huff, and Emily Miller 
*Wine and Viticulture Department, Cal Poly San Luis Obispo, 1 Grand Avenue, San Luis Obispo, CA, San Luis Obispo, CA 93407 (lcasassa@calpoly.edu)

Microwave-assisted extraction (MW) at 1,200 Watts for 10 min to 45°C and MW of stems at 1,200 Watts for 10 min to 60°C were applied to musts and stems of Cabernet Sauvignon, Merlot, and Syrah grapes from the Central Coast of California. Grapes were made into wine in 60 L fermentors, applying the following treatments in triplicate (n = 3): control; MW of the must prior to fermentation 
(MW); 100% stem addition (100%-stems); and 100% stem addition + micro-wave of the stems prior to fermentation (MW-stems). Percentages of stems in the clusters were 6.5, 3.8, and 4.5% in Cabernet Sauvignon, Merlot, and Syrah, respectively. In Cabernet Sauvignon wines, addition of stems (with or without MW) lowered wine color saturation (C*) and the red component (a*), while MW did not enhance color: MW-stems significantly increased tannin content relative to 100%-stems and these two treatments also showed higher concentration of catechin. In Merlot, only 100%-stems lowered saturation and a*. While MW did not enhance color, addition of stems increased tannin content by 46% (MW-stems) and by 19% (100%-stems), and these two treatments also showed higher concentration of catechin. In Syrah, only MW-stems lowered wine color saturation (C*) and a*, while MW was not significantly different from the control in most color parameters. Addition of stems increased tannin content by 29% (MW-stems) and by 40% (100%-stem addition) and, like in Merlot and Cabernet Sauvignon, these two treatments also showed higher concentration of catechin. A two-way ANOVA with interactions including all treatments and varieties indicated that 100%-stems consistently reduced anthocyanins, but this effect did not manifest in MW-stems. Application of MW to musts prior to fermentation had no effect on anthocyanins, tannins, or wine color, but MW-stems enhanced tannin extraction and anthocyanin concentration relative to the 100%-stems.

Funding Support: Agricultural Research Institute (ARI) New Investigator Grant (#17-03-007)

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