molecules Review A Review on Stems Composition and Their Impact on Wine Quality Marie Blackford 1,2,* , Montaine Comby 1,2, Liming Zeng 2, Ágnes Dienes-Nagy 1, Gilles Bourdin 1, Fabrice Lorenzini 1 and Benoit Bach 2 1 Agroscope, Route de Duillier 50, 1260 Nyon, Switzerland;
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[email protected] (F.L.) 2 Changins, Viticulture and Enology, HES-SO University of Applied Sciences and Arts Western Switzerland, Route de Duillier 50, 1260 Nyon, Switzerland;
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[email protected] Abstract: Often blamed for bringing green aromas and astringency to wines, the use of stems is also empirically known to improve the aromatic complexity and freshness of some wines. Although applied in different wine-growing regions, stems use remains mainly experimental at a cellar level. Few studies have specifically focused on the compounds extracted from stems during fermentation and maceration and their potential impact on the must and wine matrices. We identified current knowledge on stem chemical composition and inventoried the compounds likely to be released during maceration to consider their theoretical impact. In addition, we investigated existing studies that examined the impact of either single stems or whole clusters on the wine quality. Many parameters influence stems’ effect on the wine, especially grape variety, stem state, how stems are incorporated, Citation: Blackford, M.; Comby, M.; when they are added, and contact duration. Other rarely considered factors may also have an impact, Zeng, L.; Dienes-Nagy, Á.; Bourdin, G.; Lorenzini, F.; Bach, B.