OBSERVATIONS ON TRACES OF COPPER IN BREWING, ESPECIALLY IN RELATION TO YEAST

Abstract

The raw materials of brewing would appear to contain amounts of copper which vary from about 5 p.p.m. in barley up to some 85 p.p.m. in hops, the latter showing considerable fluctuation. The mean figure for brewery pitching yeast over a long period is 102 p.p.m., calculated on the dry material. Draught beers average 1·5 p.p.m. and bottled beers 0·9 p.p.m. The critical copper content at which fermentation is affected appears to be between 5 and 10 p.p.m. Yeasts are examined during their progress from the culture stage with virtually no copper content, through the culture room stainless-steel plant to the brewery, where successive generations are analysed after fermentations in copper vessels. A copper content is attained which appears unlikely to be exceeded in normal circumstances; in the experiments described this approached 175 p.p.m. Trace amounts of copper are recorded for the various stages of a complete brew. From this work it appears that spent grains and spent hops have comparatively high copper contents, whilst some copper is eliminated with the first yeast heads. The difficulties of obtaining truly representative samples from large bulks, and the contribution of variable amounts of copper from the plant involved, are apparent from the results.