The increase in the supply of so-called natural wines, a niche market that is close to 2% of the current French wine production, responds to a search for authenticity and a health promise, essentially through the reduction of inputs, particularly sulphites. This expectation seems legitimate and must be taken into account. However, in the frame of climate changes there is a major risk in decreasing acidity and increasing alcohol levels of wines. Mastery of processes and knowledge of microbiological phenomena have, for example, enabled oenologists for several decades to substantially reduce doses of sulfur dioxide used. Thus, the doses of total authorized sulphites could be discussed. However, various alterations that had disappeared with the contribution of oenological science are encountered again and can be elevated to the rank of qualities! The faults, whether they are related to the quality of the grapes, to uncontrolled fermentation, or to technical failure, are numerous and can reappear:
-The mousy taint generated by strains of yeast of the Brettanomyces type and of certain Lactobacillus;
-The change of microbial origin, in which lactic acid bacteria degrade tartaric acid to give wines without acidity but rich in CO2;
-Bitterness caused by a bacterial attack on glycerol to give acrolein (toxic);
-Lactic acid bacteria of the genus Pediococcus producing glucans which gives wines an oily texture.
-Ethyl acetate produced by oxidative yeasts and to a lesser extent by those used in wine making;
-In addition, ethanal is produced by yeasts (nutritional deficiencies in particular promote their formation) during alcoholic fermentation and by oxidation during ageing. It is toxic at high concentration and must be controlled, and SO2 in this case remains an essential ally with the technical mastery of the moment of its addition.
For these reasons, management of natural wine in comparison with organic wine and conventional wine production needs to be considered specifically in order to guarantee quality for the consumers. Levels of sulfur dioxide or possible antioxidant alternatives should be deeply studied in order to offer the best winemaking and ageing processes for future possible definition of natural wines in particular.
