dossier

Grapes and water stress

[vc_row full_screen_section_height=”no”][vc_column][vc_column_text]I PIWI, or resistant varieties, which we recently talked about, are just one of the possible responses to climate change. Climate instability is a complex problem, which affects not only the vine itself and, therefore, its metabolism, but also the development of pathogens. Prolonged periods of environmental conditions close to the optimal ones for the development of the pathogen, such as temperature and relative humidity) lead to more serious epidemics (think of Drosophila Suzuki), especially in the case of polycyclic subjects.
Variations in temperature and humidity influence their reproductive rate, thus increasing the evolutionary potential of individual populations.

The scenario that is emerging is that of a growing increase in the average alcohol content of wines, driven not only by higher temperatures but also by long periods of drought that favor sugar concentration and, ultimately, alcohol content. Added to this is the search for maturity and fruit, which has characterized winemaking over the last 20 years during which planting techniques have been adopted aimed at combating a series of particularly humid years.

The combination of these techniques (from low-yield clones to high planting density, to green harvesting and defoliation) and the climate change has multiplied the desired effect, leading in the opposite direction. In fact, if we compare the great Italian reds, Piedmontese and Tuscan, of the 60s and 70s with those of the 90s, we go on average from concentrations of 12,5% ​​vol. up to 13,5% to conclude with the current 14-14,5%.

While an immediate change in planting distances is unthinkable, other options are sometimes possible: consider how much the pergola training system in the case of Soave is proving to be helpful in the driest years, or the combination with Trebbiano, which is better able to conserve acidity, has proven to be a winning tactic for 2015.

Alternatively, in Spain they have been working for two years on yeasts capable of lowering the alcohol content of a wine by up to four degrees, without altering its organoleptic profile. The team of the Consejo Superior de Investigaciones Científicas coordinated by Ramon Gonzales and in collaboration with the Spanish company Agrovin has managed to manage the metabolism of yeasts so that they produce less alcohol starting from the same amount of sugar. Up to now the methods used are based on the selective elimination of part of the sugars, before fermentation, or of ethanol in the post-fermentation phase, procedures that are often aggressive for the sensorial balance of the wine.

This time, however, unconventional yeasts were used that are able to “breathe” part of the sugar in the must instead of fermenting it, thanks to a controlled supply of oxygen: “the more sugar the yeasts consume through respiration, the more the alcohol content of the wine will be reduced.” is currently working on optimizing the process with the aim of carrying out pilot experiments already in the next harvest.

 

Mach's doctoral thesis recently focused on water stress and its consequences for grapes. Stefania Savoy, awarded by the Italian Society of Viticulture and Enology as the best thesis for 2016 and which will be presented next May at the Enoforum in Vicenza when we will have the opportunity to explore it further. 

In her thesis, the researcher from Trentino studied the effects of moderate water stress on the physiology of grape development and ripening in white and red grape varieties using a multidisciplinary approach that included two years of field experiments, transcript analysis using RNA sequencing, and large-scale metabolite analysis.

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