WINETECH Technical Yearbook 2020

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indicator of mouthfeel and colour stability), total tannins (as indicator of structure) and total polyphenols. It can inter alia be used to monitor the ripening process or compare vineyard blocks. These data also influence cellar decision making, like the stage of harvesting, tannin additions, fermentation temperature, rackings, press fractions and extended skin contact. The bound anthocy- anin-tannin ratio can be used as a quality indicator and 20% can be set as aim for Cab- ernet Sauvignon with a bound anthocyanin concentration of 200 mg/L and a tannin concentration of 1 000 mg/L (Rieger, 2019). Phenol analyses of grapes and wine can be a handy tool prior to and during winemak- ing, but are rather used to observe trends, instead of interpreting absolute values. REFERENCE Rieger, T., 2019. Managing phenolics in the vineyard and winery. Wine Business Monthly , April 2019: 44-51.

berries suppresses the phenolic pathway for colour formation. The nitrogen con- centration in berries also correlates with the yeast assimilable nitrogen (YAN) of the resulting grape juice. Cultivar differences regarding phenols are a complex interaction between anthocyanins and total polyphenols, which is not yet un- derstood clearly. Co-pigmentation is respon- sible for the shift between red and violet colour nuances and can also increase the colour intensity, colour stability and colour extractability or combinations thereof. Fla- vons are the most influential co-pigments and certain anthocyanins form co-pigments more readily. Cultivars like Pinot noir and Sangiovese have low concentrations of fla - vons and the mentioned anthocyanins, which consequently limit co-pigmentation and cause that both cultivars have little colour. Phenolic analyses of grapes can include free and total anthocyanins (as colour indicator), bound anthocyanins (as

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Chemical structure of phenols.

conditions, like light, nitrogen deficiencies, cultivar and co-pigmentation, better. Light exposure promotes colour formation, while higher temperatures above 36,5°C cause colour degradation. Innovative practices, like the orientation of the vine row, are con- sequently required where light exposure is obtained without direct sunlight. Regulated nitrogen deficiency promotes colour for - mation even if the same berry mass, sugar and acid concentrations are maintained. It happens because surplus nitrogen in the

can be determined at different stages, but the most general are at veraison, a fort- night and one week before harvest, at har- vest and at different stages of production, like alcoholic fermentation and rackings. Analyses that are executed after alcoholic fermentation can inter alia be used for compiling blends, oxygen management, determining sulphur dioxide levels and the use of wood. Optimal colour in red wines can be ob- tained by understanding certain vineyard

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