The sediment that falls out of suspension in a wine is referred to as the lees. Managing these lees properly can have a great deal if influence on the quality of your wine. Shortly after pressing your wine or after fermentation you will get a very thick bed of lees. These are referred to as the "Gross Lees" and as you will see, they are not good. After racking off the gross lees, a very fine layer of lees will very slowly build up on the bottom of the storage vessel. These lees are the fine lees, which can serve several benefits to the wine depending on the style that you are going for.
Gross Lees are Gross
If a thick layer of gross lees is left on the bottom of the vessel (usually after active fermentation has stopped), the wine quality can turn south very rapidly. Even towards the end of active fermentation, it is wise to churn up any lees that start to settle as the fermentation slows. These lees contain billions of yeast cells that will become stressed when piled into an oxygen devoid sludge. Under stressed circumstances, yeast produces hydrogen sulfide which smells like swamp gas or rotten eggs. When this happens, the resulting wine is referred to as overly reductive. It is not the end of the world, and often a reductive wine can be fixed by aeration or chemical methods like copper sulfate but it is always best to just avoid the problem all together if you can.
Aside from the stinky situation above, the gross lees can become home to spoilage bacteria. The sludgy pile is rich in nutrients to feed many unwanted organisms that might stand a fighting chance now that the yeast has settled down or stopped. The goal after fermentation is to create nutrient free or low nutrient environment so that unwanted yeast strains or microbes do not have anything to munch on and cannot take hold of your wine.
Managing the Gross Lees
After pressing a red wine, allow 24 to 36 hours for these heavy particles to settle to the bottom of the carboy or storage vessel. The wine will become noticeably less cloudy and you will see a thick bed of sediment on the bottom of the container. Your racking cane should have a small plastic cup that attaches to the bottom of the cane side. Fix this cup to the cane, and place just on top of the lees before racking the wine.
If you are fermenting a white wine, stir up the heavy lees once a day (towards the end of fermentation) until fermentation is complete then follow the same steps as with a red wine. The gross lees are less of a problem if they are not allowed to compact into a dense layer on the bottom of the tank, so it is important to churn them up if this happens before the end of fermentation.
Fine Lees are Fine
During the aging period you will slowly see a thin layer of fine lees accumulate on the bottom of the tank, barrel, or carboy. Generally these are not a problem and can provide just enough nutrition to allow malolactic fermentation (MLF) to take place. There is usually no hurry to get the wine off of the fine lees, especially if you plan on performing malolactic fermentation.
Fine Lees on an Apple Wine
Benefits of Fine Lees
Some white wine producers will stir the fine lees for a year or more. This process is called bâtonnage and can help to increase the mouth feel and complexity of the wine. This process is rarely used in red wine production, because the lees can slowly pull pigmentation from the wine if brought back into suspension during aging.
Lees management is one of the many aspects of winemaking that can make or break your end product. To learn more about winemaking, checkout my youtube channel by clicking the link below. Be sure to click subscribe if you would like to be notified about new videos.
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