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)
