Maturation of Wine
Sur Lie Ageing for White Wines
Certain wines, especially certain white wine varieties such as Chardonnay and Sauvignon Blanc (especially barrel fermented) from the Loire valley and Burgundy in France, are often matured on the yeast lees referred to as sur lie (French for on the lees) after fermentation. This usually is in the same barrel in which fermentation occurred or in stainless-steel tanks with yeast lees. When a fermentation ceases, the suspended particles settle rapidly and form a sediment in the bottom of the fermentation barrel or tank. The sediment, referred to as lees, usually consists of macerated grape tissue, and dead yeast cells. The composition is variable depending upon several factors including fruit quality (incidence and type of rot), variety, processing techniques, timing of racking, and malolactic fermentation.
Benefits of Sur Lie for White Wines
There are several reasons as to why a winemaker may choose the sur lie method of wine production. The most important reason being the influence of yeast lees on the organoleptic properties of wine. Sur lie aging is stylistic in nature as lees can be enriching and beneficial to the wine, giving it improved body, enhanced flavor, and aroma complexity. Lees contact contributes complexity by integrating yeast characteristics with existing fruit and wood flavors adding greater depth of flavor.
Mannoproteins
When yeast lees autolyze, they release colloidal polysaccharides like mannoproteins that provide a degree of sweetness as a result of binding with wood-derived phenols and organic acids. This promotes harmony of some of the wine's structural elements, mainly softening tannins. Mannoproteins have a wide range of effects on the sensory properties and stability of wine (Howard, 2013):
Potential Risks with Sur Lie
One of the problems associated with sur lie aging is the formation of volatile sulfur compounds, of which hydrogen sulfide is the most common, that may impart unpleasant reduced aromas to wine when present at sensorially significant concentrations (Section 1.7). Unwanted volatile sulfur compounds are more likely to form when initial juice solids are above 200 nephelometric turbidity units (NTU). It has been reported, performing sur lie in tanks increases the likelihood of volatile sulfur compounds, which one reason why sur lie is typically performed in oak barrels.
Maturing Wine Sur Lie in Oak Barrels
Generally, wines stored sur lie in oak barrels have a much lower perception of astringency and a greater integration of the phenolic elements. Lees components such as polysaccharides and proteins are known to react with phenolic compounds, thus reducing astringency resulting in a softening of mouthfeel.
Managing Sur Lie
Batonnage
Batonnage (ba-tun-AJH) is a French term which refers to the stirring of a wine to bring yeast back into suspension. Employing batonnage in winemaking enriches the wine as lees stay in contact with the wine, helps lees absorb oxygen which reduces the risk of unwanted oxidation, and helps maintain stability in the wine. Stirring also reduces the development of reductive (i.e., absence of oxygen) off-odor sulfur-containing compounds (e.g., hydrogen sulfide and mercaptans) in the wine.
Gross Lees vs. Fine Lees
Lees can be classified as either gross or fine lees and many winemakers prefer to utilize fine lees as opposed to gross lees. Gross lees derive its meaning from the French word for heavy. Gross or heavy lees are defined as comprising of large particles (greater than 100 microns) including yeast, bacteria, tartaric acid salts, precipitated tannins, colloids, and particles formed from fining treatments and typically settle within 24 hours immediately post-fermentation (Hornsey, 2007).
Glucanase Enzymes
Generally, yeast autolysis is relatively slow (in the absence of glucanase enzyme addition) and may require months to occur, possibly impacting the mannoprotein concentration. Some winemakers treat the lees with exogenous beta-glucanase enzymes to increase mannoproteins and glucans in a wine (Chapter 20).
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