Yeast are living organisms that are classified as a type of fungi. When treated well, they survive most conditions to which winemakers subject them. If the physical and nutritional needs of yeast are understood, they can be encouraged to perform at their peak while converting juice into wine. Adverse conditions can put a stress on yeast cells and hinder their performance. In some cases, yeast may even stop fermenting or create unpleasant flavors and/or aromas in the wine.

A major growth factor for a yeast cell is nitrogen. Yeast assimilable nitrogen (YAN) target levels for healthy fermentations vary by grape sugar content (°Brix) and maturity level. High Brix (°B) juice/must requires more nitrogen than low Brix must. For example, the 21°B must target YAN level is 200 mgN/L while a 27°B must target YAN level is 350 mgN/L.

Supplementation with Fermaid K, Fermaid O, Phosphate Titres and/or DAP in low and medium YAN musts is recommended. To optimize the nitrogen uptake during fermentation, use Go-Ferm or Go-Ferm Protect during yeast rehydration. Later, add Fermaid K or Fermaid O (plus Phosphate Titres) at 1/3 sugar depletion.