Yeast Assimilable Nitrogen (YAN) is necessary for yeast growth and fermentation activity in grape must. It is comprised of two major components, amino acid nitrogen (AAN) and ammonia nitrogen (AN). Maintaining an adequate supply of YAN is essential for a successful fermentation, as both deficiency and excess of nitrogen can cause problems. Low YAN levels can lead to slow or stuck fermentations due to poor fermentation vigour, with associated increased production of hydrogen sulphide. High YAN levels can result in increased fermentation vigour, which can lead to increased volatile acidity in the final wine. Residual nitrogen at the completion of fermentation can also increase the risk of microbial instability. Several studies have confirmed that a typical must requires a minimum YAN of 140mg/L to successfully complete fermentation (Bell & Henschke, 2005). This value should be used as a rough guide though, as higher concentrations may be required depending on yeast strain, must sugar content and fermentation conditions.
YAN status was determined for Chardonnay and Shiraz grape samples from the Granite Belt during the 2012 growing season. 22 samples were received from 9 wineries. Samples were analysed for ammonia nitrogen by enzymatic analysis and amino acid nitrogen by NOPA assay.
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