racking which removes the bulk of dead yeast cells is often referred to as the gross lees as opposed to the less coarse fine lees that come as the wine continues to settle and age. During the time that the wine spends in contact with the lees, a number of changes can impact the wine due to both the autolysis (or self-metabolize) of the dead yeast cells as well as the reductive conditions that can develop if the lees are not aerated or stirred (a process that the French call bâtonnage). The length of time that a wine spends on its lees (called sur lie) will depend on the winemaking style and type of wine. The process of leaving the wine to spend some contact with the lees has a long history in winemaking, being known to the Ancient Romans and described by Cato the Elder in the 2nd century BC. Today the practice is widely associated with any red wines that are barrel fermented, Muscadet, sparkling wine Champagne as well as Chardonnay produced in many wine regions across the globe. Typically when wines are left in contact with their lees, they are regularly stirred in order to release the mannoproteins, polysaccharides and other compounds that were present in the yeast cell walls and membranes. This stirring also helps avoid the development of reductive sulfur compounds like mercaptans and hydrogen sulfide that can appear if the lees layer is more than 10 cm (4 inches) thick and undisturbed for more than a week. Most of the benefits associated with lees contact deals with the influence on the wine of the mannoproteins released during the autolysis of the yeast cells. Composed primarily of mannose and proteins, with some glucose, mannoproteins are often bound in the cell wall of yeast with hydrophobic aroma compounds that become volatilized as the cell wall breaks down. Not only does the release of mannoproteins impart sensory changes in the wine but they can contribute to tartrate and protein stability, help enhance the body and mouthfeel of the wine as well as decrease the perception of bitterness and astringency of tannins. Secondary fermentation The production of Champagne and many sparkling wines requires a second fermentation to occur in the bottle in order to produce the carbonation necessary for the style. A small amount of sugared liquid is added to individual bottles, and the yeast is allowed to