DNA-free editing to improve stress resilience of wine grape genotypes recalcitrant-to-regeneration

Past VitisGen projects (VitisGen, 2012-2017, and VitisGen2, 2017-2022) generated groundbreaking technologies for the grapevine breeding community, from low-cost DNAmarker platforms to advances in computer vision phenotyping.

This paper focuses on how taste in wine (and other foods) changes and the implications of this process
for producers and merchants.
It draws primarily on the changing taste of and taste for champagne in Britain in the 19th century. Between 1850 and 1880 champagne went from a dosage level of around 20% (20 grams sugar / litre) to 0%. Champagne became the ‘dinner wine of the elite – drunk with roast meat and savoury dishes.
Contemporaries accepted that while most people could distinguish the taste of good champagne from that of bad, very few could distinguish very good from good.

In the pursuit of more sustainable viticulture, many winegrowers have drastically reduced nitrogen (N) fertilisation and abandoned chemical weed control in favour of permanent grass cover.

The wine sector plays a significant role in the international agri-food industry, with the winemaking process leading to the generation of considerable amounts of by-products. Among these by-products, grape pomace, is one of the most abundant resources, mainly finding application in the production of distillates, fertilizers, and animal feed.

The objective of the present work is to assess yeast effects on the development of wine varietal aroma throughout aging and on wine longevity.

Three independent experiments were carried out; two fermenting semi-synthetic musts fortified with polyphenols and aroma precursors extracted from Tempranillo (1) or Albariño (2) grapes and with synthetic precursors of polyfunctional mercaptans (PFMs), and a third in which a must, mixture of 6 different grape varieties was used. In all cases, fermentations were carried out by different Saccharomyces cerevisiae strains and one S. kudriavzevii, and the obtained wines were further submitted to anoxic accelerated aging to reproduce bottle aging. The volatile profile of the wines was analyzed using several chromatographic procedures, in order to provide a comprehensive evaluation of wine aroma. Aroma compounds analyzed included fermentation volatile metabolites, grape-derived aroma compounds including PFMs, and Strecker aldehydes (SA).

Results revealed that the effects of yeast on wine aroma throughout its self-life extend along three main axes:

1. A direct or indirect action on primary varietal aroma and on its evolution during wine
aging.

2. The direct production of SA during fermentation and/or their delayed formation by producing the required reagents (amino acids + dicarbonyls) for Strecker degradation
during anoxic aging.

3. Producing acids (leucidic, branched acids) precursors to fruity esters. More specifically, and leaving aside the infrequent de novo formation, the action of the different strains of yeast on primary varietal aroma takes four different forms:

1.- Speeding the hydrolysis of aroma precursors, which leads to early aroma formation without changing the amount of aroma formed. In the case of labile molecules, such as linalool, the enhancement of young wine aroma implies a short-living wine. 2.- Metabolizing the aroma precursor, reducing the amounts of aroma formed, which can be of advantage for negative aroma compounds, such as TDN or guaiacol; 3.- Transforming grape components into aroma precursors, increasing the amounts of aroma formed, as for ethyl cinnamate, leucidic acid or vinylphenols; 4.- Forming reactive species such as vinylphenols able to destroy varietal polyfunctional mercaptans.

Overall, it can be concluded that the yeast carrying alcoholic fermentation not only influences fermentative wine aroma but also affects to the wine varietal aroma, to its evolution during aging and to the development of oxidative off-odors