Linking wine sensory properties with harvest date (part 1)

Harvest
grapevine-berry-ripening-harvest

Knowing when to harvest is a key step in the making of a good wine. Why is the timing of harvest so critical? How can harvest date affect the sensory perception of astringency in the final wine?

In a previous blog post, we described three components of fruit maturity: technological, phenolic and aromatic. Picking the optimal harvest window is challenging because of the complex response of these components to climate and vineyard practices. This post outlines common methods used by vineyards to determine harvest dates.

Many winemakers will claim that the most reliable tool they have to decide when to harvest is their palate. Winemakers taste the fruit on the vine to anticipate sensory perception in the final wine. While successful, this method is not practical or always reliable since each individual palate can produce different results.

On top of that, what the mouth tastes may not always reflect what will be extracted into the wine. To support such decisions, more winemakers are now backing up pre-harvest berry-tasting comments with fruit analysis.

Historically, analysis of sugars and acids found in the pulp have been the main chemical indices to track fruit ripeness. However, as aridity and heat wave frequency increase, fruit-sugar accumulation and acid degradation happen earlier because the pulp is essentially made of water.

Consequently the levels of sugar or acid concentrations are often disconnected from compositional changes observed in seeds and skin compartments, where flavanols responsible for bitterness/astringency are found. This phenomenon, referred to as an ‘asynchrony’ in ripening, has been reported widely by teams of researchers – for instance, in France by Garcia de Cortazar and in Australia by Sadras.

It is speculated that warmer temperatures during the growing season cause such asynchrony. To understand the extent of asynchrony, winemakers increasingly rely on analysis of flavonoids (particularly flavanols and anthocyanidins) regardless of pulp composition. A number of tools are available to help vineyards to gauge fruit composition and coloration pre-harvest such as Multiplex Signature.

These new insights offer a great opportunity to strengthen the bridge between viticulturists and winemakers. They require an understanding of fruit skin and seeds flavanols’ response to seasonal variations such as light exposure, drought or higher temperatures.

The original version of this post was published here.

Fruition Sciences offers a full suite of products addressing a variety of vineyard monitoring needs to enhance fruit and wine quality. Multiplex Signature, one of our latest offerings, helps vineyards optimize harvesting decisions based on fruit color areas and anthocyanin accumulation.

Thibaut Scholasch
Thibaut holds a Ph.D. in viticulture from the French National Institute of Agronomy at Montpellier, France. His research focused on vine water status variations under dry climates and their consequences on berry ripening. Thibaut also serves as a scientific consultant for various high end vineyards in Napa Valley. Prior to his Ph.D., Thibaut worked as a winemaker for various companies throughout the world (Chile, California, France and Australia). In 2001, he was hired by Robert Mondavi winery as a research viticulturist: his projects focused predominantly on mapping the vineyard variability, analyzing vineyard practices and vine water deficit impact on fruit composition. Thibaut earned a Masters degree in Viticulture and Enology in 1997 and a Masters degree in Winemaking in 1998 from SUPAGRO, one of the top agronomy school in France.
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