Yeasts: the changing winemaking

[vc_row full_screen_section_height=”no”][vc_column][vc_column_text]There are two branches of winemaking where innovation is taking decisive steps, which in the coming years will lead to an important, if not revolutionary, change in the world wine panorama.
Last December, the RIVE event held in Pordenone allowed us to take a closer look at both of these themes.

PIWI
The first concerns resistant varieties, the so-called PIWI (read ALEA article), capable of counteracting fungal diseases.
Developed in Germany decades ago, thanks to their resistance, they require fewer treatments and therefore allow for more sustainable viticulture.
It should be emphasized that to date there are no varieties resistant to either primary diseases, such as powdery mildew and downy mildew, or secondary diseases, such as Drosophila Suzuki (read ALEA article).
The PIWI Association, founded in 2000, has over 350 members from 17 different countries in Europe and North America.

At the international level, interest in the Pilzwiderstandfahig, this is the exact name , it is such a competition was organized, the International Piwi Awards , precisely to evaluate in blind tasting the new varieties that are gradually developed in the various countries.
For its part, Italy is not standing by and watching: the Rauscedo Cooperative Nurseries have, in fact, started serial experiments on the same ones for almost a decade, with increasing requests from markets like France where current regulations require a 30% reduction in treatments. Fleurtai, Soreli, Sauvignon Nepis, Merlot Khantus are just some of these varieties.

At the moment in Italy 19 PIWI varieties have been registered in the National Register of Varieties, of which 10 are white and 9 are black.
The biggest obstacle in Italy for PIWIs remains the fact that wines produced with these varieties can only aspire to IGT but neither to DOC nor DOCG.
YEASTS

The second branch of oenology that has brought and is bringing about important changes concerns yeasts, which in the last 50 years have crucially changed the ability to manage the fermentation phase, leading to wines that are cleaner in aromas, more balanced and also have greater aging potential.
While on the one hand industrial yeasts have allowed – also thanks to technologies such as temperature management – ​​less turbulent and more predictable fermentations, on the other hand many producers are approaching with ever greater interest native yeasts, which are naturally found on the skin of the grapes and which allow to further strengthen the territoriality of a product.

YEASTS IN DIGENI

The enthusiasm for indigenous yeasts that initially involved mainly natural and biodynamic wine producers has not left even less “purist” companies and businesses indifferent.
Examples of this are the Barolo, Raboso and Brunello denominations that have long been investing in the development of so-called “territorial yeasts”, with appropriate laboratory selection to isolate the best strains.
Some have already gone further, such as the Asolo Consortium which has decided to use local yeasts to create the consortium bottle that represents the Treviso denomination.
"We started working with indigenous yeasts a long time ago - he says Viviana Corich of the University of Padua – qwhat has changed is not so much the yeasts themselves, but their taxonomy” which has allowed us to better understand its nature and functioning today.
So if 20 years ago candidiasis was seen as negative, today universities and research centers look at these fungi with renewed interest.
An example for everyone?
La Starmerella Bacillaris (Candida zemplinina) which is more resistant to alcohol and has a notable fructophilic character.

Even today, when certain mechanisms are clearer, there remains a major issue in the management of indigenous yeast fermentation, namely the presence of multiple strains that add complexity to a dynamic that is already unpredictable and linear.
SELECTED YEASTS

And if the so-called native yeasts allow to strengthen the territorial vocation, the selected ones develop new paths, such as the management of alcohol that in increasingly warm and dry years, with a growing accumulation of the sugar content - and therefore of the potential alcohol - will prove to be a winning card.
It was 2015 when the research of a team from the Consejo Superior de Investigaciones Científicas, led by Ramon Gonzales in collaboration with Agrovin, which has tested a method capable of reducing the quantity of alcohol in a wine by up to four degrees, without altering its organoleptic profile.
The researchers managed the yeast metabolism so that they produced less alcohol from the same amount of sugar.
The unconventional yeasts that succeed “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.".
The aim, the researchers point out, is not to produce wines without alcohol, but "try to compensate for the effects of the excess sugar with which the grapes enter the cellar more and more frequently. Usually, the methods used are based instead 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.”

Historically, yeasts have been selected for their fermentation capacity, fermentation kinetics at different temperatures, production of low amounts of acetic acid and resistance to sulfur dioxide.
However, recently other criteria are also taken into consideration such as:
- the ability to strengthen the color thanks to the metabolic formation of stable pigments and the low absorption of anthocyanins by the yeast cell wall
- the absence of beta-glucosidase activity which prevents color degradation
- the facilitation of colloidal stabilization in red wines obtained thanks to a rest on the lees
- the enhancement suitable for aroma thanks to the production of volatile components such as esters and higher alcohols, together with the low production of unpleasant flavours
- the creation of structure and body thanks to the production of poly-alcohols such as glycerol and 2,3-butanediol and the release of mannoproteins and polysaccharides.[/vc_column_text][/vc_column][/vc_row]