Since the early 1990s, we've understood the importance of lees and the role of yeast autolysis products. This is why they are used from one vintage to the next in Burgundy.
Mainly composed of dead yeast and bacterial cells, lees are of multiple interest for wines. Their self-degradation through autolysis releases compounds such as proteins, mannoproteins, amino acids, lipids, peptides, polysaccharides,.. At every stage of the winemaking process, lees can be used to improve the quality of the future wine.
- Improved turbidity following fining of must from an altered harvest (mildew, oidium, Botrytis...)
In some years, the sanitary state of the harvest requires severe settling, or even fining, to eliminate the harmful compounds responsible for aromatic deviations. The musts obtained are then very clear and do not allow optimal alcoholic fermentation.
"Reserve" lees (healthy lees from the previous vintage) can then be used to enhance turbidity and enrich the must with nitrogen compounds.
- Provide organic nitrogen, survival factors and detoxify fermenting musts.
During alcoholic fermentation, assimilable nitrogen is a survival factor for yeasts. Lees, which are rich in nitrogen compounds thanks to autolysis, provide nutrients to promote good alcoholic fermentation. What's more, in some years, alcoholic fermentations languish. This is partly due to the presence of short fatty acids, that inhibit yeast. They act on membrane permeability and prevent the functioning of internal enzymatic systems. As a result, sugars no longer penetrate the yeast cell and can no longer be metabolized. The use of cell envelopes (yeast hulls derived from yeast autolysis) removes this inhibition by binding toxic fatty acids. In addition, these lees provides new long fatty acids and sterols to reinforce the cell walls of the living yeast.
- Supply nitrogen and specific nitrogen fractions, necessary for the development and multiplication of lactic acid bacteria.
Unlike yeast, lactic acid bacteria are unable to produce nitrogen resources. However, they can metabolize compounds present in the environment, notably amino acids (arginine, cysteine, glutamate,...) and small peptides. These elements, necessary for the proper development of Oenococcus oeni populations, can be added to the wine by oenological products developed using inactivated yeasts.
The use of fresh lees from the previous year is an alternative to these products, providing the wine with the nutritive compounds essential for the multiplication of lactic bacteria populations and optimizing malolactic fermentation kinetics.
- To carry out fining following problems of oxidation, bitterness, reduction or false tastes.
During our applied research in Burgundy, we experimented with the role of fresh lees as a fining agent on wines presenting bitterness, reduction, oxidation and other false tastes (vegetal notes, mustiness, etc.).
For example, during a major reduction, the lees are able to bind the undesirable compounds responsible, such as methanethiol and ethanethiol. When added to the wine, the mannoproteins contained in these fine lees form a complex with these sulfurous molecules, enabling them to be neutralized. Similarly, they can treat wines with a “musty taste” by adsorbing chlorophenols and chloroanisoles.
Thanks to their reducing power, lees can also be used to treat oxidative wines.
Their adsorbing power enables them to fix and eliminate a multitude of undesirable compounds in wines, revealing cleaner, clearer wines when tasted.
- Create a source of improvement in the taste and body of white wines, and create a "reducing buffer" effect.
During alcoholic fermentation, yeast synthesizes amino acids, including three sulfur-containing amino acids: cysteine, glycine and glutamate. Together, they form a tri-peptide: glutathione. A veritable shield against oxygen, glutathione is released by the lees during ageing.It acts as a reducing buffer, protecting the wine's aromas.In the bottle, it complements the protective role of the obturator, CO2 and SO2. White wines with high gluthation concentrations (several mg/L) and low pH are more resistant to bottle ageing.
Lees also release glutamic acid during aging (concentration triples between the beginning and end of aging on lees with bâtonnage). This amino acid acts as a flavor enhancer.
Mannoproteins, proteins derived from the yeast wall of lees undergoing autolysis, have a material effect. They give the wine sweetness, smoothness and volume.
Mannoproteins also act as protective colloids. Enzymatically detached from cell envelopes, they inhibit the formation of potassium hydrogen tartrate crystals. Prolonged ageing on lees, coupled with enzymatic treatment, avoids the need for chilling and promotes wine stability.
Reused from one vintage to the next, fresh lees offer multiple advantages at every stage of the winemaking process, from must to wine. They play a fundamental role in Burgundy wines.