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​55. The effect on fermentation by-products of the amino acids in wort

Takuya Hashimoto, Suntory Liquors Limited, Osaka, Japan

 

ABSTRACT: Amino acids in the wort, measured as free amino nitrogen (FAN), are extracted during the mashing process and are essential nutrients for sufficient fermentation performance. Too low a level of amino acids causes incomplete fermentation due to insufficient nutrition of the yeast, but too high a level remaining in the finished beer may negatively affect sensory variables such as foam quality. Therefore, for good fermentation, it is necessary to ensure the appropriate quantity of amino acids in the wort. In this study, we investigated the influence of fermentation conditions that differed in the amount of amino acids in the wort with most variables held constant. We made the wort at 12.0°P with 115, 160, and 230 mg/L of FAN and fermented. This showed that the more FAN in the wort, the more isoamyl acetate was produced. We analyzed the relationship between the quantity of this ester and the amount of the amino acids valine and leucine, which are biosynthetic precursors of isoamyl acetate. As expected, in the wort with low FAN content, valine and leucine were depleted during fermentation, inhibiting the formation of isoamyl acetate. The uptake of amino acids involved in yeast metabolism during fermentation is also connected with the generation of sulfur compounds, so the quantity of FAN also correlated with the quantities of hydrogen sulfide (H₂S) and sulfur dioxide (SO₂). Thus, the FAN utilized by the yeast during fermentation was confirmed to be an important factor determining the quality of the beer. In conclusion, in addition to being an essential yeast nutrient for fermentation, FAN in the wort is involved in the biosynthesis of a number of fermentation by-products. In particular, we found that the quantity of isoamyl acetate can be controlled. This suggests that the adjustment of FAN is a factor that can control the flavor of the beer.