Wines & Vines

GRAPEGROWING BY Bruce Zoecklein, Professor Emeritus and former Head of the Enology-Grape Chemistry Group, Virginia Tech. b-1,3-glucanase. b-1,3-glucanase is active during yeast growth and during élevage in the presence of non-multiplying yeast cells. Stirring increases the concentration.9 Lees mannoproteins can impact the following: • ntegration of mouthfeel elements by i interaction between structural/textural elements,3,10 • eduction in the perception of r astringency and bitterness,5,11,19,23 • increase wine body,3 • encourage growth of microorganisms,13 • impact bitartrate instability,14,16,17,25 • impact protein stability,26 • nteract with wine aroma i components.15 Lees management considerations Several methods of increasing mannoprotein levels in wine have been suggested,6,10 including: • must turbidity, • election and use of yeast that produce s high levels of mannoproteins during alcoholic fermentation, • east that autolyze rapidly upon y completion of alcoholic fermentation, • ddition of b-1,3-glucanase to wines a stored on lees, • ddition of exogenous mannoproteins a (proprietary products), lysated (broken) lees. The amount of mannoprotein released during yeast fermentation is dependent on several factors, including Photo by Elizabeth Clark, Airlie Winery, Oregon raditionally, only some white wines and sparkling wines were left in contact with yeast lees postfermentation. This practice is now used frequently in many viticultural regions around the world today for both red and white wines.20 Lees are composed mainly of yeasts, bacteria, tartaric acid, polysaccharides and protein-tannin complexes. Red wine lees have a relatively high concentration of protein and tannin. The composition is variable depending upon several factors including: fruit quality (incidence and type of rot), cultivar, processing techniques, timing of racking, malolactic fermentation (MLF) and timing and use of enzymes, etc. Lees contribute to colloidal macromolecules in wine that are derived from three general sources: polysaccharides, glucans and mannoproteins.10 Mannoproteins are proteins with a high carbohydrate content including mannose sugars, hence the term. During aging sur lie, a breakdown of yeast cellular membrane components can occur, releasing intracellular constituents. These macromolecules can positively influence structural integration, phenols (including tannins), body, aroma, oxygen buffering and wine stability. Some macromolecules provide a sense of sweetness as a result of bridging the sensations among the phenolic elements, acidity and alcohol, aiding in wine harmony and integration. yeast strain. Large differences are noted among yeasts in the amount of mannoproteins produced during fermentation and released during autolysis. Generally, the more turbid the must, the lower the mannoprotein concentration in the fermented wine.12 Mannoproteins released during yeast fermentation are more reactive than those released during the yeast autolysis process in modifying astringency. This helps provide additional justification to measure the non-soluble solids of juice (NTUs) pre-fermentation. In Burgundy and other regions, red wines are sometimes aged on their yeast lees in conjunction with addition of exogenous b‑1,3-glucanase enzyme. This procedure is an attempt to release mannoproteins, which winemakers believe may enhance the suppleness of a wine, while reducing perceived astringency. Wines aged on lees with no fining contain mannoproteins, while wines fined prior to aging may have a large percentage of mannoproteins removed. Periodic stirring sur lie increases the mannoprotein concentration and increases the native b-1,3-glucanase activity. Generally, yeast autolysis is relatively slow (in the absence of glucanase enzyme addition) and may require months or years to occur, possibly impacting the mannoprotein concentration. 2 Mannoproteins Mannoproteins in yeast cell walls are bound to glucans (glucose polymers) and exist in wines as polysaccharides and proteins.10 They are released from cell walls by the action of an enzyme, 74 p racti c al w i ne ry & v i ne yard AU GU ST 20 13 Red wine lees remain after Pinot Noir wine is racked out of the fermentor.

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