Unfortunately, like most things in life I suppose, too much of a good thing can be bad…and sometimes even dangerous. Although there is a significant upside to the use of healthy, “light” lees, there can be a very destructive downside! And this of course, is what every winemaker wants to dodge…
Some of the solid particles and flakes which form part of lees may be the origin of vegetal aromas and flavors, sometimes up to a point where it almost smells a bit reduced. I have heard the term “sauerkrauty” which is actually a very good descriptor for this phenomena, as it refers to both the elements of vegetal and reductiveness. Another potential risk is the fact that our “friend” the bisulfite ion, which, to a certain degree has an anti-microbial function (although not as significant as molecular SO2), as well as some free SO2, are also bound by these solid particles. Of course in the bound form, SO2 lose most of its antimicrobial function and probably all of its anti-oxidative properties.
This of course is a time bomb, simply because we are now managing all the good microbes in parallel with the high risk ones from which we are normally “protected” as a result of the effects of SO2: Brettanomyces, Pediococcus, Lactobacillus. And – the higher the pH, the higher the risks.
Another risk related to lees contact is the development of reductive odors and metallic tastes. The release of these sulfur compounds may be the result of light lees that is very tightly compacted during wine maturation. This phenomenon is potentially even more hazardous in situations where reductive odors appeared during primary fermentation.
The release of “bitter” substances in wines, combined with reductive and “Brett like odors” is another risk associated with lees contact and is related to contamination by living yeasts such as Brettanomyces and Pichia, as well as lactic acid bacteria like Pediococcus. We are well aware of exactly where they come from: insufficiently disinfected cellar equipment, lack of optimal SO2 management, high pH’s and the release of nutrients into the wine as a result of autolysis.
And speaking of release of nutrients…living lactic acid bacteria may have the ability to metabolize different amino acids with the production of biogenic amines. Hence the importance of hygiene and optimal SO2 management!
What do I propose?
To keep it simple. Manage hygiene. Manage SO2 and pH optimally. Taste frequently. And great will be your reward.