Excessive nitrogen supply and shoot trimming can impair colour development in Pinot Noir grapes and wine


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We investigated the effects of nitrogen supply and shoot trimming on mature, field-grown Pinot Noir (Vitis vinifera L.) vines. Ammonium nitrate (0, 30, 60, 90 kg N/ha) was applied at the beginning of flowering. Shoots were topped either once (at fruit set), or twice, (at fruit set and during the lag-phase of berry growth). Neither treatment affected grape berry and skin weights, yield and grape sugar, but high rates of nitrogen increased malic acid and reduced skin phenols, flavonols and anthocyanins. Malvidin-3-glucoside was the most abundant anthocyanin in skins and wine. It accounted for 75% of the total anthocyanins at the beginning of fermentation and its relative proportion increased to 95% in the finished wine.

Increases in anthocyanin concentration at the beginning of fermentation and before malolactic fermentation, were followed by declines during the later stages of alcoholic and malolactic fermentation. High nitrogen supply decreased anthocyanins in the juice and wine, increased pH and increased the percentage of malvidin-3-glucoside. Repeated shoot topping gave lower wine total phenols and anthocyanins and thus enhanced the nitrogen effect. Wine susceptibility to oxidation increased with higher pH and lower anthocyanin content. The best treatment combination for fruit and wine quality, in terms of colour and oxidative stability, was low nitrogen/single topping and the worst combination was high nitrogen/repeated topping. These results suggest that a combination of high rates of nitrogen fertiliser and repeated shoot trimming can decrease potential fruit and wine quality.