Multi-Year Study of the Chemical and Sensory Effects of Microwave-Assisted Extraction of Musts and Stems in Cabernet Sauvignon, Merlot and Syrah Wines from the Central Coast of California

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.

Keywords: anthocyanins; microwave; phenolic compounds; sensory analysis; stems; tannins; wine color.

Figure 1

Evolution during bottle aging of selected phenolic classes and wine color in the wines of the 2016 vintage. Different letters in the last sampling point (12 months of bottle aging), indicate significant differences for Fisher’s LSD test and p < 0.05. Mv-3-G.: malvidin-3-glucoside equivalents; AU: absorbance units; CE: catechin-equivalents.

Figure 2

Visual depiction of the actual color of the 2016 wines of the three cvs. and four winemaking treatments as seen through a 1 mm path length quartz cuvette at the time of pressing (day 12). ΔE* values are shown between each pair of treatments for a given cv.

Figure 3

Evolution during winemaking, early and extended bottle aging of selected phenolic classes and wine color in the wines of the 2017 vintage. Different letters in the last sampling point (12 months of bottle aging), indicate significant differences for Fisher’s LSD test and p < 0.05. Mv-3-G.: malvidin-3-glucoside equivalents; AU: absorbance units; CE: catechin-equivalents.

Figure 4

Evolution during winemaking and extended bottle aging (36 months) of monoglucosilated, acylated and anthocyanin-derived pigments. (A) Cabernet Sauvignon; (B) Merlot; (C) Syrah. Mv-3-G.: malvidin-3-glucoside equivalents.

Figure 5

Evolution during winemaking and extended bottle aging (36 months) of quercetin derivates, other flavonols and flavonol aglycones. (A) Cabernet Sauvignon; (B) Merlot; (C) Syrah. Qc-3-G.: quercetin-3-glucoside equivalents.

Figure 6

Visual depiction of the actual color of the 2017 wines of the three cvs. and four winemaking treatments as seen through a 1 mm path length quartz cuvette at the time of pressing (day 12). ΔE* values are shown between each pair of treatments for a given cv.

Figure 7

Evolution during winemaking and extended bottle aging of selected phenolic classes and wine color in the wines of the 2018vintage. Different letters in the last sampling point (12 months of bottle aging), indicate significant differences for Fisher’s LSD test and p < 0.05. Mv-3-G.: malvidin-3-glucoside equivalents; AU: absorbance units; CE: catechin-equivalents.

Figure 8

Visual depiction of the actual color of the 2018 wines of the three cvs. and four winemaking treatments as seen through a 1 mm path length quartz cuvette at day 1100 (32 months of bottle aging). ΔE* values are shown between each pair of treatments for a given cv.

Figure 9

Sensory scores (10 cm unstructured line scale) of Merlot and Syrah wines from the 2016 vintage assessed by a sensory panel. Different letters within a sensory descriptor indicate significant differences for Fisher’s LSD test and p < 0.05.