The Basics of Lees

Lees are one of the many fascinating things about wine that many people do not know the significance about. Sometimes, there are phrases on the label of a bottle that says, "aged on lees" or "stirred on its lees". I thought it would be fun to do some explanation on what this means.

Lees are basically sediments that end up at the bottom of a barrel or stainless steel tanks after fermentation or aging the wine. They are made up of stuff like grape pulp, seeds, dead yeast cells and other particles remaining in the wine after fermentation. What happens during the winemaking process is that the wines are being separated from the lees to avoid yeast autolysis. This separation is usually done by racking the wines into another storage vessel. We will get to what is yeast autolysis later on. However, there are occasions when the winemaker decides to add some complexity and mouthfeel to the wines. That is when they decide to leave the wines on some of the lees and this is called lees contact. The French call it "sur lie". This practice of wine making has been done since the days of the Romans and is usually followed by what is called bâtonnage by the French or lees stirring. This is an additional and optional practice by winemakers. Both practices enhances the mouthfeel of the wine by releasing mannoproteins, which binds with proteins to make the wine less astringent.

Both practices are done mostly on white wines especially for Chardonnay and Muscadet de Sèvre et Maine sur Lie (also known as Melon de Bourgogne), but not so much for red wines unless the winemakers intend to make their reds go through malolactic fermentation or MLF in short. I will get to MLF later on as well. Burgundy and other wine-producing countries are known for using these practices for their Chardonnay. The final product usually results in a creamier Chardonnay with flavours such as cheese, bread, toast, vegemite, custard and custard. Some people would describe the combination of these characters as leesy.

Muscadet de Sèvre et Maine sur Lie is a wine that is most famous in the Loire for being light, fresh, crisp and mostly neutral in flavor. The wine is served cold and goes wonderfully with oysters. The wine is bottled from the tank of cask after being on its lees all winter, developing more body and yeasty character to it. Some of the best Muscadets are bottled directly from the barrels without any racking or filtration, leaving behind some of the lees in the bottle. The lees act as natural antioxidants which give the wine its freshness.

Although sur lie is a method used by winemakers to make their wines more complex, they are not without potential problems. When wines are left on a thick layer of lees at the bottom of the storage vessel for more than a week, the wine starts to develop unpleasant smells caused by sulfide. This happens because the dead yeasts in the lees start to "eat themselves up" and consume oxygen in the process. The same lees that gives Muscadet its freshness by consuming oxygen gives the wine an off-odour as well. That is why some Muscadet smells like rotten eggs or stale. Racking the wine is important to prevent the lees level from becoming too thick.

Bâtonnage is often used when the white wines are to go through fermentation in the barrel. The stirring is done by a stick. The purpose of lees stirring is to prevent the formation of the thick layer of lees at the bottom of the barrel so that sulphur won't develop into hydrogen sulfide from the lack of oxygen. Stirring up the lees also allows the lees to act as a partial barrier between the wine and the wood to prevent the wines from extracting too much tannins from the oak into the wine.

Now we are getting to the part about autolysis. This takes place when the dead yeast cells digest itself by its own enzymes. Autolysis is something which winemakers try to avoid in their wines except for sparkling wines. The dead lees are left in the sparkling wine after its second fermentation in the bottle that produces the CO2 gas that we all love. This aging on lees in the bottle can sometimes go up to five years or maybe more, improving the mouthfeel and imparting flavor characteristics such as flowers, biscuit bread and other complex aromas.

Lees also provides for micro-nutrients to lactic bacteria so that MLF can take place in the wine. MLF is a process in which lactic bacteria converts the sharper malic acid into the soft, rounder lactic acid. The wine becomes less crisp and more creamy. Many Chardonnays go through MLF in the barrel so as to get extra complex flavours such as caramel, butter or butterscotch. Winemakers tend to be careful about excessive MLF as they do not want to produce too much diacetyl, the component which imparts the buttery aromas.

So next time when you come across this terms, at least you can tell your mates about what it means. Hopefully, by knowing a little more each day, you become a smarter drinker and a smarter consumer.