Wine
made from grapes subjected to accelerated ripening, an increasingly
frequent phenomenon occurring in many wine regions due to peaks of
heat and water stress, displays higher alcohol levels and lacks balance
with color and flavor compounds. Herein, the rate of sugar accumulation
of grapes was manipulated by varying the crop load and irrigation
regime and the development of secondary metabolites was monitored
by gas chromatography–mass spectrometry (GC–MS) and
high-performance liquid chromatography (HPLC). A 3-week delay in ripening
correlated to an increase in the concentration of some monoterpenes
and norisoprenoids and a greater decrease of green aroma compounds.
Delayed ripening had a positive impact on the phenolic composition
of grapes, displaying higher contents of total anthocyanins, total
phenolics, quercetin glycosides, and polymeric pigments. A map of
the chemical composition of grapes close to harvest allowed discrimination
of compounds mainly responsive to delayed ripening from those driven
by crop load or irrigation.
Several vineyard techniques have been proposed to delay grape maturity in light of the advanced maturation driven by increasingly frequent water and heat stress events that are detrimental to grape quality. These studies differ in terms of their experimental conditions, and in the present work we have attempted to summarize previous observations in a quantitative, data-driven systematic review. A meta-analysis of quantitative data gathered across 43 relevant studies revealed the overall significance of the proposed treatments and evaluated the impact of different experimental conditions on the outcome of antitranspirants, delayed pruning and late source limitation. Antitranspirants were most effective when applied twice and closer to veraison, while di-1-p-menthene increased the ripening delay by about 1°Brix compared to kaolin. Larger ripening delays were achieved with delayed pruning of low-yielding vines or by pruning at later stages of apical bud development. Late defoliation or shoot trimming delayed ripening in high-yielding vines and represent suitable solutions for late-harvested varieties, but became ineffective where the treatment decreased yield. This quantitative meta-analysis of 242 primary observations uncovers factors affecting the efficacy of vineyard practices to delay ripening, which should be carefully considered by grape growers attempting to achieve this outcome.
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