Alleviation of the effects of nitrogen limitation in high gravity worts through increased inoculation rates

Abstract

There are few inexpensive, practical methods to increase the usable nitrogen level in a substrate to be fermented to a potable alcohol product, but the provision of adequate assimilable nitrogen to a fermentation medium is critical for rapid and full "wort" attenuation. One practical solution to circumvent the problem may be to increase the inoculation rate to much higher than recommended levels. In this work, an increase in the pitching rate from 1.6×107 cfu/ml to 8×107 cfu/ml was shown to alleviate fermentation problems caused by nitrogen limitation. Attenuation and ethanol production rates became independent of the initial wort-free amino nitrogen (FAN) concentration, as did yeast viability and maximal yeast cell number. However, the final total cell mass was lower if the wort was nitrogen-deficient, regardless of the pitching rate. These cells were smaller and/or lighter and contained less protein at the end of fermentation. Such yeast could cause problems in subsequent fermentations if reuse of yeast (common in brewing) was considered. © 1991 Society for Industrial Microbiology.