Grape maturity: Are your berries ready for harvest?

vineyard technology

Several definitions exist to characterize grape berry maturity: technological, aromatic, polyphenolic, and enological:  
  • Technological maturity is the time point beyond which berries do not accumulate more sugar and do not lose any more acidity.
  • Phenolic maturity takes into account the quantitative and qualitative evolution of the berry polyphenols in the skin (anthocyanin and tannins) and seeds (tannins).
  • Aromatic maturity is characterized by the optimal concentration of aroma and volatile compounds.
However, none of them is really satisfactory as a stand alone because ripeness depends on a combination of those different ripeness levels.

As air temperature gets warmer, technological maturity occurs sooner in the growing season while phenolic maturity and aromatic maturity may occur earlier as well, but not shift as much. In a warming context, achieving an earlier technological maturity makes it more difficult to find the ideal harvest window.

Determine the optimal harvest date with enological maturity

Ultimately, wine growers only consider enological maturity to determine harvest date. The enological maturity tries to account for all the forms of maturity described. Therefore, the berries harvested at enological maturity show a high sugar/acidity ratio, high anthocyanin content in the skin, and low astringency. However, harvest time is still mostly determined empirically, based on crude biochemical composition (sugar, acid content, total polyphenols,..) and berry tasting. It is therefore important to understand the physiological and molecular basis of berry ripening that lead to enological maturity.

Assess fruit maturity profiles

In a context of more elevated temperatures, technological maturity is reached before phenolic and aromatic maturity. To optimize harvest decision, it becomes increasingly critical to identify early the stages leading to phenolic and aromatic maturity. Practically, winemakers can better evaluate the timing when aromatic and polyphenolic maturity is reached by tracking successively the preliminary steps leading to technological maturity:
  • when berry growth stops
  • when sugar accumulation slows down or stops
  • when acid degradation stops

Once such preliminary stages have been reached, more complex analysis can be done on the fruit such as:

  • anthocyanin analysis : to monitor skin color degradation with time
  • tanins analysis: monomeric component like flavon-3-ols (to monitor seed lignification) or polymeric component like epigallocatechin
  • polyphenols extractibility analysis: to assess what will really be found into the wine after fermentation and maceration
  • aromatic profile analysis: except for volatile compounds, which are directly perceptible by olfaction, there are many odorless compounds in grapes, called varietal precursors. During wine making, they can generate odoriferous compounds.

Conclusion

By analyzing and tracking the compounds driving technological maturity, you can improve the timing for analysis of aromatic and polyphenolic maturity. Given the current climatic trend, this knowledge becomes increasingly strategic to refine optimal harvest window.

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