[Un article de The Conversation écrit par Evelyne Aguéra – Ingénieur d’études en fermentation oenologique, Inrae – et Mouret Jean-Roch – directeur de recherche en bioprocédés, Inrae]
Due to climate change, particularly rising temperatures and drought, the quality of grapes, the raw material for making wine, is changing.
On the one hand, due to greater maturity and partial drying of the grapes, the sugar level of the grapes increases and consequently the alcohol level of the wines (because the final alcohol content of the wine is directly proportional to the sugar content of grape juice). On the other hand, the levels of nutrient elements (nitrogen, lipids, vitamins, minerals) present in the grapes and used by the yeasts during the production of wine are modified, with consequences on the production of aromas during fermentation. alcoholic.
Indeed, a significant part of the aromas involved in the taste of wines are produced by yeasts (Saccharomyces cerevisiae) during fermentation. Therefore, a modification of the composition of the raw material will have a direct impact on the synthesis of aromas and therefore the taste of the wine.
An evolution towards fruitier and lighter wines
So, in this context of climate change, how can we continue to produce quality wines, which respond to current consumer tastes and the market's evolution towards more fruity, aromatic and light wines?
We work on all types of wine. Our research activities (carried out within Inrae in Montpellier and Gruissan) focus on the development of innovative strategies for controlling the fermentation process to optimize the production of aromas by yeast in wines (maximization of positive aromas and limitation of organoleptic defects).
These strategies are based on the use of selected yeasts and optimal management of nutrient supply to optimize the production of aromas by the yeast. Our job is to better understand the role of different factors and to propose the best possible strategies.
Alcoholic fermentation: fine chemistry
During alcoholic fermentation, the yeast mainly transforms the sugars in the grape juice into ethanol and carbon dioxide. Yeast also produces a large number of volatile molecules, notably fermentation aromas such as esters which are mainly responsible for the fruity notes of wines.
The synthesis of these aromas depends on several factors: yeast strain, fermentation temperature, nutrients naturally present in grape juice or added during the process (sugars, lipids, nitrogen, vitamins). The major challenge is to find the optimal combination between these different factors to obtain a wine with an aromatic quality adapted to consumer demand.
Laboratory studies have demonstrated the importance of adding nutrients and managing temperature on the progress of fermentation and the production of aromas. The interactions between the different factors complicate the understanding of the mechanisms involved.
For example, our research has demonstrated the key role of nitrogen nutrients in the production of isoamyl acetate, a compound involved in the aroma of banana and fresh fruit, which are sought-after aromas for light wines. and fruity.
It appears that an addition of nitrogen mid-fermentation is more effective than an initial addition in the same quantity. However, there are strong interactions between the effects of nitrogen, lipids and temperature; it is therefore necessary to have a combined management of these different factors to maximize the final content of this positive aroma in the wines.
The aromatic quality of a wine is of course not linked to the sole presence of isoamyl acetate but to a large number of other volatile molecules, it is necessary to have a global vision of the production of the different aromas during fermentation.
Therefore, to have a more precise understanding of alcoholic fermentation, we have developed real-time sensors allowing simultaneous monitoring of the bioconversion of sugar into ethanol and the production of aromas by yeasts in winemaking tanks.
These sensors made it possible to acquire data on the kinetics of aroma production throughout fermentation, which is much more useful and interesting than the simple acquisition of the final concentrations of the molecules of interest and which makes it possible to control production. of all the aromas as fermentation progresses.
The data generated made it possible to develop mathematical modeling predicting the effects of different fermentation parameters (nitrogen, temperature management) on the progress of fermentation and therefore the production of associated aromas.
Control fermentation very carefully
This mathematical model allows us to develop innovative strategies for controlling the fermentation process. It thus becomes possible to maximize the content of this or that positive aroma and also to define a real-time control strategy for the process making it possible to obtain a target value for a group of desired aroma molecules.
In the latter case, the idea is to guarantee the consumer an aromatic quality of the wine, while trying to limit the vintage effect and/or to best manage the impact of climate change and climatic accidents – hail, floods, etc. . – by adapting the production process.
The wine industry is today facing a multifactorial crisis: drop in consumption, loss of competitiveness on international markets, hazards and climate change, etc. Research must offer solutions to enable it to achieve greater resilience in this unfavorable period. The transfer to industry players of our research work on innovative strategies for conducting the fermentation process is an example of this.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
