Determine yeast nutrient additions based on current and target YAN levels.
Measured in the lab or estimated from previous vintages
Primary ammonia nitrogen present in the must
Calculated as: FAN + (Ammonia × 0.8235)
Typically 150-250 mg/L for most fermentations
DAP is ~21% nitrogen by weight, while organic nutrients are typically ~10% nitrogen
Yeast Assimilable Nitrogen (YAN) is a critical metric in winemaking, referring to the total amount of nitrogen available for yeast metabolism during fermentation. Adequate YAN levels are essential to ensure a complete and healthy fermentation, reduce the risk of hydrogen sulfide (H₂S) production, and avoid stuck or sluggish ferments. YAN is composed primarily of two fractions:Free Amino Nitrogen (FAN) andammonia (typically measured as NH₃-N).
FAN consists of individual amino acids and small peptides naturally present in grape must. It is derived from grape proteins during berry development and is influenced by grape variety, vineyard nitrogen status, ripeness, and viticultural practices. FAN serves as a readily metabolizable nitrogen source for yeast. It is typically measured via ninhydrin assay, and is expressed in mg/L. FAN contributes directly to yeast biomass production and fermentation kinetics, but it does not provide all necessary nitrogen forms required by the yeast.
Ammonia nitrogen, present as ammonium ion (NH₄⁺) in must, is another vital source of nitrogen for yeasts. Unlike FAN, ammonia is typically quantified via enzymatic assay and is expressed in mg/L of NH₃-N. In YAN calculations, ammonia is multiplied by a factor of 0.8235 to convert to an equivalent YAN contribution. This factor accounts for the molecular weight ratio and conversion of nitrogen mass. While ammonia is efficiently assimilated by yeast, excessive levels can be inhibitory or lead to undesirable fermentation characteristics.
The sum of FAN and ammonia-derived nitrogen gives the totalYAN. Typical YAN requirements vary by yeast strain and fermentation conditions but generally range between 150–250 mg/L. High-sugar musts, low-temperature ferments, and certain commercial yeast strains may require levels above 250 mg/L. If YAN is deficient, nutrient additions (e.g., diammonium phosphate or organic yeast nutrients) are necessary to ensure fermentative success and sensory quality.
Accurately measuring and adjusting YAN allows winemakers to manage fermentation proactively. Over-supplementation, however, can result in excessive biomass, elevated fermentation temperatures, and elevated ethyl carbamate precursors. Therefore, nitrogen management should be targeted based on actual lab analysis and winemaking goals.