Abstract
Yeast assimilable nitrogen (YAN) is essential for yeast growth and metabolism during apple (Malus x domestica Borkh.) cider fermentation. YAN concentration and composition can impact cider fermentation kinetics and the formation of volatile aroma compounds by yeast. The YAN concentration and composition of apples grown in Virginia, USA over the course of two seasons was determined through analysis of both free amino nitrogen (FAN) and ammonium ion concentration. FAN was the largest fraction of YAN, with a mean value of 51 mg N L−1 FAN compared to 9 mg N L−1 ammonium. Observed YAN values ranged from nine to 249 mg N L−1, with a mean value of 59 mg N L−1. Ninety‐four percent of all samples analyzed in this study contained <140 mg N L−1 YAN, a concentration generally considered the minimum level needed in grape‐based wines for yeast to fully utilize all of the fermentable sugars. FAN concentration was correlated with total YAN concentration, but ammonium concentration was not. Likewise, there was no correlation between FAN and ammonium concentration.
Highlights
Yeast assimilable nitrogen (YAN) is an essential nutrient for yeast growth and metabolism during fruit juice fermentation
The fact that cider fermentations are conducted with lower soluble solids concentration than wine fermentations has led some in the cider industry to hypothesize that the YAN concentration required for apple fermentations could be lower than those required for grape juice fermentation
Grape juice for wine production generally contains higher concentrations of both total YAN and ammonium ions than we currently report in apple juice
Summary
Yeast assimilable nitrogen (YAN) is an essential nutrient for yeast growth and metabolism during fruit juice fermentation. YAN is composed of ammonium ions and free amino nitrogen (FAN). Yeast metabolism is influenced by the interaction between yeast strain (Julien, Roustan, Dulau, & Sablayrolles, 2000) and the chemical composition of YAN (Torrea et al, 2011). Ammonium is preferentially assimilated by yeasts (Jiranek, Langridge, & Henschke, 1995a) and can be the sole YAN source used to complete fermentation (ter Schure, van Riel, & Verrips, 2000). Fermentations with high FAN concentrations lead to desirable flavor production in grape- based wines as compared to ammonium alone (Torrea et al, 2011)
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