A SYSTEM OF WORT ANALYSIS. PART III: THE ESTIMATION OF ASSIMILABLE NITROGEN IN WORTS BY YEAST UPTAKE AND BY WORT ANALYSIS

Recent work has strengthened the view that the amount of assimilable nitrogen in brewery worts is an important factor in yeast nutrition; yet comparatively few estimations of assimilable nitrogen have been recorded. Instead, the total nitrogen and the free amino nitrogen content of worts have often been used as measures of assimilable nitrogen, so that it has been necessary to find good methods for these different estimations and to find the relationship between them. In a method suggested as standard, the assimilable nitrogen has been measured by determining the nitrogen taken up by the growth of a small inoculum of pure culture yeast under conditions aiming to eliminate errors due to infection, acidity, bios and mineral shortage, incomplete absorption, nitrogen excretion from yeast and protein precipitation from wort. This method appears to give a well‐defined figure, and, under these conditions, the nitrogen of amino‐acids added to wort appears to be completely absorbed. A comparison has been made between this direct determination of assimilable nitrogen and estimations on the same worts of total nitrogen content, free amino nitrogen content and “nitrogen not precipitated by phosphotungstic acid and zinc sulphate.” In pale worts each of these estimations was found to bear a fairly good relation to the assimilable nitrogen; but, when dark worts were included, only the free amino nitrogen still provided a good measure of assimilable nitrogen, and therefore a reliable and rapid method for the estimation of the assimilable nitrogen of worts.