Influence of Grape Seeds and Stems on Wine Composition and Astringency

Abstract

The aim of this paper is to study the real influence of seeds and stems on wine composition, astringency, and bitterness. A decolored grape juice and a grape juice macerated for 4 days from the same Cabernet Sauvignon grapes were fermented with or without supplementation with 100% seeds, 300% seeds, or 100% stems. Once alcoholic fermentation had finished, the wines were analyzed and tasted. The presence of seeds and stems increased the concentration of flavan-3-ol monomers with respect to the controls. However, the seeds mainly released (+)-catechin and (-)-epicatechin, whereas the stems mainly released (+)-catechin and (+)-gallocatechin. The seeds and stems also released proanthocyanidins; those from seeds have a lower mDP and a high percentage of galloylation, whereas those from stems have a higher mDP and a relatively high percentage of prodelphinidins. The presence of seeds and stems brought about a slight but significant increase in pH and lowered titratable acidity and ethanol content. The presence of seeds boosted color intensity, whereas stems had the opposite effect. Finally, both seeds and stems increased wine astringency and bitterness.

Preliminary Study of the Effects of Pulsed Electric Field (PEF) Treatments in Wines Obtained from Early-Harvested Sangiovese Grapes

“…According to results, two mechanisms were hypothesized: (i) increased mashing of solid parts of grapes by electric pulses, and contextual increase in the anthocyanins content in the musts/wines, as previously reported [29][30][31]; (ii) increased extraction of polyphenolic precursors (i.e., flavonoid compounds, and proanthocyanidins) which contributes to the color improvement and stability in young wines [32][33][34]. A possible impact of the PEF treatment on the buffer capacity and tartaric stability of wines can be postulated, most likely based on the release of ionic species (primarily, potassium) from the woody parts of grapes, i.e., seeds and residual stems [35].…”

he Impact of Different Tannin to Anthocyanin Ratios and of Oxygen on the Phenolic Polymerisation Over Time in a Wine-like Solution

“…Grape anthocyanins and condensed tannins (proanthocyanidins) are the most important groups of phenolic compounds in red wines due to their involvement in determining the colour and sensory properties (Cheynier et al, 2006;He et al, 2012aHe et al, , 2012b. Anthocyanins are normally exclusively extracted from the grape skins, whereas condensed tannins also originate from the grape skins, stems and seeds (Meyer & Hernandez, 1970;Pascual et al, 2016). Differences in the chemical structure, polymer length and % galloylation of grape tannins can influence their extractability (González-Manzano et al, 2006), reactivity and thereby their final impact on the sensory properties of wines (Peleg et al, 1999).…”

“…However, the oxygen intake should be controlled to avoid excessive production of acetaldehyde and subsequent over-polymerisation and precipitation (Castellari, et al, 2000;Du Toit, et al, 2006a;Ribéreau-Gayon, et al, 2006). The ageing potential of a wine seems to be influenced by the nature of the tannins and the relative A/T ratios (Singleton & Trousdale, 1992;Ribéreau-Gayon et al, 2006;Pascual et al, 2016;Picariello et al, 2017), but this needs further clarification. Two recent publications have evaluated the oxygen consumption of several oenological tannins in a model wine solution, showing how the different nature of the tannins (model wine solutions rich in ellagitannins, gallotannins, skin tannins or seed tannins) influence the oxygen consumption rates (Pascual et al, 2017;Vignault et al, 2018).…”

Study of the effectiveness of a strain ofSaccharomyces cerevisiaeselected for the production of wines with higher acidity and lower alcoholic strength

“…Moreover, some of the sugars are used by yeasts to increase their biomass, and a percentage of ethanol is evaporated in a greater or lesser extent depending on the CO 2 release rate, the temperature and the dimensions of the tank. Moreover, some winemaking operations such as pumping over can also favor its evaporation [7,8].…”