Harvest 2015: Low YANs

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December 12, 2015

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It is just the middle of Feb and harvest is well underway. We’ve heard reports that it’s the earliest in 35 years, with some winemakers telling us they are harvesting certain varieties up to 4 weeks earlier.

From our side, the report is another season of very low YAN levels. Samples with <10mg/L ammonia and YAN’s <100mg/L have not been uncommon at the lab.

HOW MUCH NITROGEN TO ADD:

  • < 21 Balling: 200-250mg/L YAN required
  • 21 – 23 Balling: 250-300mg/L YAN required
  • 23 – 25 Balling: 300-350mg/L YAN required
  • > 25 Balling: 350-400mg/L YAN required

BALANCING YEAST NUTRITION:

Yeasts need balanced levels of amino and ammonia nitrogen to ferment efficiently. Instead of using just DAP, a complex nitrogen blend should be used which also contains amino acids, vitamins, minerals and yeast hulls.

The nitrogen (YAN) concentration of a complex nutrient should be determined (from the supplier) so that accurate addition rates may be calculated.

  • Ammonia-N: In grape juice, the quantity of amino-N is greater than that of ammonia-N. If only DAP or ammonia is added to the juice, the natural balance is disturbed, especially if large amounts of DAP/ammonia are added, for e.g.in highly nitrogen deficient musts. This can result in less efficient fermentations and the production of H2S.
  • Amino acids: Amino-N is added to juice in the form of yeast extracts. Primary grown yeast extracts contain a wide range of amino acids required for efficient yeast metabolism.
  • Vitamins: Vitamins are found in many yeast extract products or as a preparation on their own. The most important vitamins for efficient yeast metabolism include pantothenic acid, thiamine and biotin.
  • Minerals: Phosphate (found in DAP), magnesium, manganese, zinc and copper are all beneficial. • Yeast hulls: Yeast hulls provide sterols for active yeasts if added towards the end of fermentation. Sterols are important in protecting the active yeasts from high alcohol levels. Sterols adsorb decanoic acid, a yeast by-product that is toxic to fermenting yeasts.
  • Oxygen: Oxygen enables yeasts to produce their own sterols required for alcohol tolerance.
  • Suspended solids: Suspended solids promote a healthy fermentation due to a high sterol and unsaturated fatty acid content.