Fermentation is crucial in producing high-quality spirits. Factors such as raw material composition, nutrient addition, and operating conditions affect yeast metabolism, growth and fermentation.
Different feedstocks vary in fermentable sugar types and amounts of assimilable nitrogen, minerals, salts and vitamins, impacting yeast activity. Tailored nutritional blends are essential for optimal fermentation and aroma/ flavor biosynthesis.
Nitrogen is vital for yeast health, required for biomass generation and protein/ DNA/ RNA synthesis. Yeast assimilates nitrogen from the fermentation media, balancing deficiency and excess.
Saccharomyces cerevisiae uses various organic and inorganic nitrogen sources, collectively known as yeast assimilable nitrogen (YAN). Inorganic sources include ammonia, ammonium hydroxide, ammonium sulfate, and phosphate salts.
Organic nitrogen includes free amino acids and small peptides. Proteases hydrolyze proteins and peptides to increase free amino nitrogen (FAN).
Nitrogen utilization is regulated by nitrogen catabolite repression (NCR), with ammonium ions assimilated rapidly and organic nitrogen gradually.
Typically, 200-250 ppm of YAN is needed for efficient fermentation. FAN measurements indicate total nitrogen content in substrates. Nitrogen management ensures consistent kinetics, with higher levels corresponding to faster fermentation. Excess nitrogen is uneconomical and less efficient.
FAN average concentration in Grain and malted grain normalized to typical initial fermentation densities. (n= number of substrates analyzed).
Measurement Methods
Various methods measure nitrogen concentration, including titration and small-scale fermentation tests. Optimal nitrogen dosage boosts fermentation kinetics and ethanol concentration.
Starch-based feedstocks, such as barley, maize, wheat, rye, oat and sorghum, are used to produce whisk(e)ys and neutral grain spirits (NGS or GNS). These feedstocks contain organic nitrogen in the form of proteins, which are not readily available to yeast.
Proteases, enzymes that break down proteins into amino acids and smaller peptides, are used to release this nitrogen, supporting yeast metabolism and potentially increasing yield by liberating bound sugars.
Protease supplementation is preferred over diammonium phosphate (DAP) addition for starch-based fermentations due to its efficiency and consistency. Proteases can be added through malt inclusion or commercial protease-based nutrients like DistilaVite HY, which offer more consistent results.
Whiskey corn mash fermentation with and without addition of a protease- based nutrient.
Nitrogen influences volatile aroma and flavor compound synthesis. Higher alcohol and esters are produced from amino acids. Higher alcohol is produced through the Ehrlich pathway, which degrades amino acids.
Acetate esters, such as phenethyl acetate and isoamyl acetate, are formed by condensing higher alcohols and Acetyl CoA. Coenzyme A, involved in synthesizing acetate and ethyl esters, is derived from amino acids. The balance between organic and inorganic nitrogen impacts flavor and aroma congener production.
Nitrogen sustains yeast growth and metabolism for efficient fermentation and congener biosynthesis. However, nutrition is more complex than just the addition of Nitrogen. Yeast needs inorganic ions and vitamins for growth and fermentation.
Inorganic ions serve as enzymatic cofactors, intra-cellular messengers, osmo-regulators, and protein components. Vitamins support metabolic enzymatic activity. Tailored nutrition optimizes fermentation efficiency, yield, and off-flavour control.
