Technical Report
 

Nitrogen Compounds in Oregon Musts and Wines

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https://ir.library.oregonstate.edu/concern/technical_reports/pz50gx34z

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  • Over the last several years many Oregon winemakers have expressed concerns over the frequency of 'stuck' and sluggish yeast fermentations. These problems are probably due to low nitrogen status of musts at harvest. Malolactic fermentations may also be affected by low levels of fermentable nitrogen in juice and wine. Low levels of assimilable nitrogen can cause nutritional stress in yeast and the production of hydrogen sulfide by degradation of grape juice proteins containing the sulfur amino acids cysteine and methionine. Nitrogen compounds (N) are used by yeast for the production of cell biomass, proteins, and enzymes necessary for the biochemical processes of fermentation. Grape juice nitrogen status can vary greatly depending on variety, soils, vineyard site, water stress, and climate (vintage). Other factors that may affect nitrogen status include grape maturity, effects ofjuice clarification prior to fermentation, fermentation practices, and differential utilization by different yeast strains. Although 400 to 500 mg of assimilable N per liter ofjuice are required for maximum yeast biomass production, about 150 mg/L is generally required to complete fermentation ofjuice to dryness. This assumes a large initial inoculum size of about 106 cellshnl or more and a typical 10-20 fold increase in yeast biomass during the course of fermentation.
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