Monday, 2 April 2018

Why dry hop? (part three)

I'm continually amazed at what grabs my readers' attention and what doesn't. I thought that the article I've based these posts on was intrguing, but rather obscure. Something only of interest to a few professional brewers.

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 :—

(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.

In the first place we found that an aqueous infusion of hop extracts less diastase from a given quantity of malt than does distilled water under similar conditions. This is shown by the following experiment :—

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.

(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.
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:—
(1) 100.0
(2) 16.1
We 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.
Infusion A    0.000 grams.
Infusion B    11.250 grams.
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.

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 tannin is contained for the most part in special cells of the leaf-tissue, and, under ordinary circumstances, does not come in contact with the diastase, which exists to a greater or less amount in the general starch-containing parenchyma. When, however, the dried leaf-issue is treated with a comparatively small amount of water, the solution of the tannin is sufficiently concentrated to prevent the diastase entering into solution. When, on the other hand, the hops are immersed in a comparatively large amount of liquid, the tannin, which diffuses first in point of time, forms such an extremely dilute solution that it has but little or no effect upon the diastase which difluses into the liquid at a much slower rate. There is another reason, also, in the case of beer why the tannin of the hopping-down hop does not arrest diastatic action. Unless beer has been very highly hopped indeed in the copper, it always contains, after the fermentation is finished, a sufficient quantity of albuminoids of the right kind to precipitate tannin from solution. This is doubtless the fate of the tannin of the hop used in dry-hopping; it is quickly removed from the sphere of action, and cannot consequently exert the least inhibitory action on the “freshening” power of the hop. In considering the results which we have recorded in this paper - results which, we think, have given a complete explanation of the influence of dry-hopping on the after fermentation of beer - no doubt certain practical questions will suggest themselves to you; and, of these, perhaps the one of greatest importance, is the bearing these experiments have on the method of curing the hops at the time they are picked. It is not long ago since we had an authoritative statement from a gentleman closely connected with hop growing, that the temperatures employed in drying on the oasts are much too low, and that hops will keep very much better if dried at a higher temperature. We do not dispute the accuracy of this statement but we must give a word of warning to hop growers who carry out this suggestion, that they will run very great risk of destroying in the hops one of those qualities which is essential to the production of a suitable article for dry-hopping."
The Brewers' Guardian 1893, pages 107 - 108.
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?

Be happy to hear the thoughts of anyone who understands this better than me.


Peter Skelton said...

Fantastic information Ron. This little series is really solidly breaking down observed phenomena and using science to explain not only the overall observation but also give a very clear explaination of exactly the mechanism and also troubleshooting the experiments which have unexpected results.

qq said...

Tannins are pretty much defined by their ability to precipitate out proteins, so although it's not anything specifically anti-diastase, it makes sense that the presence of tannins will knock out diastase activity.

I''m not sure why you'd have hops in your mash tun before mashing is complete though?

As for the popularity of the topic - well, you do have articles that are recipes for homebrewers, so it's not surprising that stuff relevant to homebrew is popular among your readership, especially anything to do with dry-hopping.