There isn't going to be much commentary from me this time. Partly because I'm not sure that I really understand it all. Partly because it's Easter and I've got better things to do.
"It must be remembered, in considering the results of this last experiment, that the influence of the yeast of the beer had been completely prevented by the chloroform, and that if the yeast had been still in possession of its functions, hydrolysis would have proceeded with even greater rapidity, as we know very well that under the combined action of organised ferments and diastase hydrolysis often goes on much more rapidly than under the influence of the diastase alone. As it seemed possible that the diastatic activity of hops might be due wholly or in part to the seed: which they generally contain, we have made comparative experiments with the hop strobiles, in one case including the seeds, and in the other after the seeds had been carefully picked out. We also append a determination of the diastatic activity of the foliage leaves of the hop plant. The results are calculated out for the amount of maltose produced from soluble starch by 10 grams of the material acting under standard conditions :—I had no idea that tannin prevented distase from going into soultion. So does that mean that too ,amny hops in the mash tun could bugger up conversion? Or am I getting this totally wrong?
(1) Hop-cones, including' seeds, 9.60 grams maltose. (2) Hop-cones, freed from seed, 2.06 grams maltose. (3) Foliage leaves of hop plant, 2.01 grams maltose.
The seeds doubtless contribute largely to the diastatic activity of hops, but the bracts of the strobiles, which are really leaf organs, have also a very marked hydrolytic effect, yet an aqueous infusion of the same hops, no matter how concentrated it maybe, is incapable of producing any diastatic in fluence. We have already referred to the difficulty there is in extracting enzymes from some kinds of tissue, owing to the tenacity with which they are retained by the cell protoplasm, but it is very seldom indeed that an aqueous extract of such tissue, when properly prepared, is entirely without action, as is the case with the hop infusion. It therefOre seemed in the highest degree probable that there was something extracting from the hop which prevented the diastase going into solution. As we know that hops contain a considerable amount of tannin, and that tannin has a very great retarding influence on diastatic action, owing to its rendering insoluble that class of albuminoids to which diastase belongs, it seemed highly probable that the tannin of the hop was responsible for the abnormal results obtained with the aqueous infusion. Such was, in fact, found to be the case.
Two dilute malt extracts were prepared:
(1) By digesting 0.5 grams of finely divided malt with 100 c.c. of water for 48 hours.On filtration the relative diastatic activity of these two extracts was determined. The relation was found to be as follows, No. I being taken at 100:—
(2) By digesting 0.5 grams of the same malt with 100 c.c. of water and 3.5 grams of hops for 48 hours.
(1) 100.0We see that in (2) the addition of 3.5 grams of hops per 100 c.c. to the extraction water has reduced the diastatic activity of the resulting malt extract to about 1/6. That this remarkable result is due to the tannin of the hops prevent. ing the diastase going into solution was proved in the following manner :—
When an aqueous infusion of hops is shaken up for a short time with some raspings of untanned hide the tannin is completely removed from the infusion, but no other constituent of the hop extract is touched.
A strong aqueous extract of hops was prepared by digesting hops with a comparatively small quantity of water for 48 hours. The filtrate was divided into two parts, A and B.
A. 100 c.c. of the hop extract was digested with 1 gram of finely divided malt for 24 hours.
B. 100 c.c., treated in a similar manner, but the tannin was first removed by shaking with hide filings.
After standing on the malt in each case for twenty-four hours the dilute malt extracts so produced were filtered off, and
their diastatic power determined. This was measured by the amount of maltose hydrolysed from soluble starch by an equal volume of each extract, all the usual conditions being fulfilled. The following numbers show the amount of maltose produce by 100 cc. of the extracts :—
Diastatic Activity.We see that in A the amount of tannin in the hop extract used had been sufficient entirely to prevent the dissolution of the diastase from 1 gram of malt; whilst in B, which differed from A merely in having had its tannin removed with hide filings, the diastase had readily gone into solution.
Infusion A 0.000 grams.
Infusion B 11.250 grams.
We are now in a position to understand how it is that it is impossible to prepare an infusion of hops showing diastatic activity, although the hop-strobile contains a very notable quantity of diastase, which is brought into action when the hops themselves are immersed in the liquid containing a hydrolysable substance.
The Brewers' Guardian 1893, pages 107 - 108.
Be happy to hear the thoughts of anyone who understands this better than me.