MOULD FUNGI AS A POSSIBLE CAUSE OF DETERIORATION OF STORED HOPS

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Abstract
It had long been established that the deterioration of hops during storage is due to an alteration in the resin content with which was associated its preservative value. Later T. K. Walker was able to show that this fall in preservative value was caused by diminution in the α-resin which was accompanied by an increase in the ß- and γ-fractions. The retardation of this change has been effected by cold storage, while it has also been claimed that storage in the absence of air, and in inert gases such as carbon-dioxide and nitrogen has also been effective in slowing up this reduction in the preservative value. The only method of storage, however, which has proved satisfactory has been cold storage, and although this very materially slows up the changes taking place in the resins it does not entirely prevent them. Although attempts have been made from time to time to account for this deterioration no definite evidence of the factors responsible has so far been forthcoming, and it might be attributed to either chemical change or enzymic activity or to the growth of organisms in the hops. In the course of his work on hop drying at the Experimental Oast at Beltring, A. H. Burgess (this Journ., 1935, 467) had occasion to consider this question of the prevention of the deterioration during storage, not only on account of its commercial importance, but with a view to preserving the season's samples for the purpose of carrying out the necessary analyses. In a series of experiments he was able to obtain sufficient evidence to prove that enzymes of hops were not the cause of the loss in preservative value during storage, and he turned his attention to the effect of living organisms. A number of fungi and bacteria were isolated from deteriorating hops, and preliminary experiments carried out with these gave evidence that at least three fungi were capable of effecting a rapid reduction in the amount of α-acid in the hops under storage conditions. Investigations of this nature involving biological characters require to be repeated several times and involve storage over long periods before definite conclusions can be drawn, it was therefore considered advisable that the experiments should be continued in view of the great importance of this question, both commercially and scientifically and of the results obtained in the preliminary experiments. The present investigation was therefore undertaken to determine to what extent the growth of moulds contributes to the loss of preservative resins in commercially stored hops, and to define the conditions of storage necessary to avoid such spoilage.

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