Abstract
Microwave technology (MW) was applied to musts and stems over three consecutive vintages in Cabernet Sauvignon, Merlot and Syrah wines from California (USA). Stems were added to musts at a rate of 50 and 100% (50% Stems and 100% Stems), either as untreated or after MW (50% MW Stems and 100% MW Stems). Stem additions lowered ethanol (up to 1.15% v/v reduction), but increased pH (up to 0.16 units) and the tannin content of the wines. In 2016, tannins increased by 103% (100% Stems), and 124% (100% MW Stems). In 2017, tannins increased by 39% in stem-added Merlot wines and by 63% (100% Stems) and 85% (100% MW Stems) in Syrah wines. In 2018, tannins in Syrah wines increased by 250% (100% MW Stems) and by 743% (100% Stems). Wines made with 50% Stems exhibited intermediate tannin contents. Must MW increased flavonols (up to 278% in Syrah wines), monoglucosylated, acylated and anthocyanin-derived pigments. Stem additions reduced wine color and polymeric pigment formation in Syrah. Must MW decreased the perception of coarseness and herbaceous flavors in Merlot, whereas stem additions increased herbaceous aromas in Syrah. Despite higher tannin contents in stem-added wines, no concomitant increases in astringency were observed.
Highlights
The time-honored motto that “wine is made in the vineyard” is widely accepted by the wine industry and empirical as well as scientific evidence appears to support this view
In this multi-year study spanning three consecutive vintages, the effect of microwave technology (MW) applied to stems and musts prior to alcoholic fermentation was studied in three different cvs., Cabernet Sauvignon, Merlot and Syrah grown in the Central Coast of California
The percentage of stems calculated based on fresh weight (FW) is shown
Summary
The time-honored motto that “wine is made in the vineyard” is widely accepted by the wine industry and empirical as well as scientific evidence appears to support this view. The statement implies that the chemical composition of the grapes (and the resulting wines) is determined by the interactions between the grape cultivar (cv.), the vineyard site, the vintage, and the applied viticultural practices. This view does not exclude the contribution of enological treatments known to affect the chemical and sensory profiles of the wines during winemaking and subsequent stages. Phenolic compounds are key component of grape and wine chemical composition They appear in grapes and wines as a rather heterogenous family of highly bioactive compounds including light-absorbing molecules such as anthocyanins and flavonols, and others able to precipitate with proteins such as tannins. Phenolic compounds rarely exceed the threshold of 4000 mg/L
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