Grapevine & Wine 03/10/2011

The boomerang effects of wine-making standardization: the case of defoliation

Mechanization reduces expenses but doesn’t normally provide the operational flexibility which is required by climate changes for the safeguard of quantity and quality

Never like this year has the vine defoliation been so important.
Defoliation is a very delicate practice since it can be very helpful in the maturation stage and in preventing some pathologies. At the same time, though, it can have some boomerang effects for the vineyard, in particular for the one which work strictly with the calendar without a proper evaluation of the climate conditions.

What it is generally suggested is to perform the defoliation in order to promote the air circulation around the grape. This grants the effectiveness of the leaves treatments for the preservation of the grape health and a better maturation of grapes, in particular as for the accumulation of anthocyanins and polyphenols.

Defoliation was traditionally done by hand just when it was necessary but the advent of mechanization allowed a strong reduction of the costs of this operation.

According to bibliography the manual defoliation is convenient just for small vineyards, below three hectares, while for the medium size ones, between three and ten hectares, mechanical defoliation convenience depends on the local cost of labor. Over ten hectares the mechanical option is always the most convenient.

The employed machines require mechanical defoliation to take place early, when grapes are still green and hard, in order to reduce possible damages.
Since the last decade it is known that the mechanical defoliation presents some cons, such as the reduction of the number and weight of grapes, and the increase of sugary degree and the phenolic and anthocyaninc components.

All this was true before the climate changes in act.
As a matter of fact, nowadays an early defoliation can induce an excessive withering of the grapes, associated with a too high sugar degree, a sugar/acidity disequilibrium and the lost of aromatic compounds, which altogether prevent the production of high quality wines. It is also well known that defoliation can be the reason for a lower wine production associated with the increase in dregs.

These problems have been posed by all the observers about the quality of the vintage 2011.
As a matter of fact, these problems were particularly clear in the last vintage, characterized by a very warm and dry August and begin of September, which forced many farms in the dilemma between quantity and quality.
Besides sparkling wines, whose grapes were harvested very early to produce wines with an adequate acidity, the most difficult choice concerned red wines: harvesting early grapes characterized by a high sugar degree, high phenolic content but low acidity or waiting some more weeks and the rains, able to restore the chemical conditions of the grapes, right for high quality wines, but loosing at least the 20% of the harvest?

However, it is still unclear if a late defoliation, commensurate with the year conditions, makes the chemical disequilibrium of the grapes better or worst.
In the smallest farms, where the defoliation was performed late (second half of August) or even not performed at all, the grape health and quantity were not compromised. At the same time, the chemical values, even if not completely harmonic, were surely more adequate to high qualitative standards. Finally, the protection provided by the leaves left around the grapes allowed those farmers a higher flexibility in the choice of the harvesting time, being the grapes less stressed compared to the one directly exposed to the sun light and warm.

The proof will be in our glasses very soon, since enology can do, but rarely it can do miracles.

di Graziano Alderighi