Yeast Assimilable Nitrogen (YAN)

Nitrogen is a critical grape nutrient for yeast growth and fermentation activity and affects the rate and completion of fermentation, fermentation bouquet and style of wine. Nitrogen is also linked to wine volatile sulfur compounds and ‘reduction’.

YAN analysis provides information on the nitrogen status of grapes, musts and juices: specifically, the amount of nitrogen available for yeast to utilise during fermentation.

Early detection of nitrogen deficiency in grapes and juice can enable winemakers to make informed decisions regarding nitrogen additions using inorganic nitrogen (di-ammonium phosphate; DAP, click here to access the DAP calculator) or organic nitrogen (proprietary yeast supplements). Nitrogen supplements can reduce the risk of slow or stuck fermentations, affect the development of undesirable sensory characters such as hydrogen sulfide and reductive character, and can modify wine style by increasing the fruity/estery profile. Excessive inorganic nitrogen can increase the risk of ester taint formation.

Analysis

YAN can be quantified by independent analysis of ammonia (NH3) and alphaamino nitrogen (αAN; also referred to as free-amino nitrogen or FAN)

[YAN] = 0.8225 * [NH3] + [αAN]

NH3 analysis can be performed by:

  • Enzymatic method
  • Ion selective electrode

αAN analysis can be performed by:

  • Nitrogen by o-phthalaldehyde (NOPA)
  • High Pressure Liquid Chromatography (HPLC)
  • Near Infra-Red Spectroscopy (NIR)

YAN concentrations range from 50 to 450 mg/L in Australia with 100 to 200 mg/L being common. Low YAN is associated with low soil organic content and overall dry growing conditions.

Recommended YAN levels in grapes/musts/juices

Minimum YAN requirement for low risk fermentation:

  • Whites – approx. 150 mg/L
  • Reds – approx. 100 mg/L

YAN requirement for clean/fruity flavour:

  • Whites – approx. 250 to 350 mg/L
  • Reds – unknown (research in progress)

Maximum YAN demand:

  • Mean = 400 mg/L
  • Range = 330 to 470 mg/L

Notes:

  1. These values are to be used as a guide and depend heavily on yeast strain and fermentation conditions (e.g. initial sugar, temperature, fermentation aeration).
  2. YAN requirement for clean/fruity flavour has only been determined in Chardonnay: low YAN juices gave more complex aromas whereas moderate YAN gave cleaner and more fruity aromas in young wines.
  3. Large additions of inorganic nitrogen (DAP) can increase risk of ester taint (ethyl acetate) formation.
  4. Higher initial juice/must YAN values increase fermentation rate and heat production.
  5. DAP can be added in divided doses to give a more moderate rate of fermentation.
  6. Higher initial juice/must YAN values or DAP additions can increase the risk of residual YAN in finished wines.

Sampling recommendations

  • Juice samples are best
    • Clarified juice for non-skin contact cultivars
    • Berry pulp and skin for skin contact cultivars; if juice samples are used, increase the YAN estimate by approx. 20%
  • Take samples as close to harvesting as possible
    • 1-2 weeks prior to harvest when weather conditions are cool to moderate
    • Several days to 1 week prior to harvest, and preferably taken from the juice/must, under hot, dry conditions
  • Fermenting juice will give misleading results
  • Omit seeds from sample preparation
  • Do not post samples for analysis without clarification and/or sulfur dioxide (SO2) addition (see Submission of samples)

References

  • AWRI staff publication # 875. Bell, S.-J.; Henschke, P.A. Implications of nitrogen nutrition for grapes, fermentation and wine. Aust. J. Grape Wine Res. 11: 242295; 2005.
  • AWRI staff publication # 1001. Vilanova, M. Ugliano, M. Varela, C. Siebert, T. Pretorius, I.S. Henschke, P.A. Assimilable nitrogen utilisation and production of volatile and non-volatile compounds in chemically defined medium by Saccharomyces cerevisiae wine yeasts. Appl. Microbiol. Biotechnol. 77 (1): 145-157; 2007.
  • AWRI staff publication # 1022. Ugliano, M. Henschke, P. Herdrich, M.J. Pretorius, I.S. Nitrogen management is critical for wine flavour and style. Aust. N.Z. Wine Ind. J. 22(6): 24-30; 2007.
  • AWRI staff publication # 1045. Cowey, G. Excessive copper fining of wines sealed under screwcaps – identifying and treating reductive winemaking characters. Aust. N.Z. Grapegrower Winemaker (531): 49-56; 2008.
  • AWRI staff publication # 1078. Coulter, A.D. Henschke, P.A. Simos, C.A. Pretorius, I.S. When the heat is on, yeast fermentation runs out of puff. Aust. N.Z. Wine Ind. J. 23 (5): 29-33; 2008.
  • AWRI staff publication # 1144. Ugliano, M; Winter, G; Coulter, A.D; Henschke, P.A. Practical management of hydrogen sulfide during fermentation – an update. Aust. N.Z. Grapegrower Winemaker. Annual Technical Issue (545a): 30-37; 2009.
  • Dukes, B.C. Butzke, C.E. Rapid determination of primary amino acids in grape juice using an o-phthalaldehyde/N-acetyl-L-cysteine spectrophotometric assay. Am. J. Enol. Vitic. 49 (2): 125-134; 1998.