Saturday, 31 March 2018

Why dry hop? (part two)

I hadn't forgotten about this. Just been resting my brain a bit.

Not that I'll be getting through all of the second instalment of the article this time. For some reason part two of the article ios three times the length of part one. A bit strange.

The theory that wild yeasts on the hops were responsible for secondary fermentation is given short shrift. And with good reason. Stuff like Brettanomyces takes a while to get going. Longer than it takes a secondary fermentation to kick off.
"WE are now in position to ascertain how far the sugars of the hop are accountable for the after-fermentation in duced of dry hopping. If we consider that the brewer uses from a half to three-quarters of a pound of dry hops per barrel, the total quantity of sugars so introduced will amount, in round numbers, to 3.5 per cent. of this quantity, that is, from eight to twelve grams of sugar per barrel. This small amount of sugar is quite incapable of producing the observed effects, and that the freshening effect is not in any way due to this cause is clearly shown also by the fact that when the dry hops are submitted fora very short time to the action of steam, and they are afterwards introduced into the beer along with the small amount of water of condensation adhering to them, they are found to have entirely lost the power of inducing an after fermentation.

The second possible explanation that the vigorous after-fermentation is induced by the hops, owing to certain organised ferments introduced by them, has received our most careful attention, and we have made a very large number of experiments in this direction, both on a small and large scale,which, to our minds, are very conclusive. We can quite confirm the observations of various previous observers, that there certainly are several small varieties of yeast naturally adherent to the hop, and that these yeasts are capable of ready cultivation in sterilised worts and beer. There can be no doubt, also, that these “wild" yeasts occasionally develop and give trouble in the beer, but close observation, both in the laboratory and on a practical scale, has shown most conclusively that the particular conditioning property of the hop to which we are now drawing attention, is long antecedent to the growth and development of these wild yeast forms, and is quite independent of them.

We have now to consider the only remaining explanation of the freshening power of the dry hops in beer, viz., that they contain a diastase capable of hydrolysing the non-crystallisable products of starch transformation, which a beer always contains.

Our first experiments were performed with aqueous infusions of hops, made by macerating a large quantity of hops with a comparatively small quantity of water for forty-eight hours, and testing the filtered extract for diastatic power by digesting known quantities with a fixed volume of a solution of soluble starch at about 35° C., a temperature favourable to hydrolysis of a diastatic enzyme is present. Under no possible conditions could we in this way obtain an extract showing any diastatic power. We varied the experiment by taking the first filtrate from the hops and making another infusion with it, again repeating this until we had obtained no trace of diastase in solution, as not the slightest hydrolysis could be brought about by the extract in solutions of soluble starch, amyloins, or beer extract.

It might, perhaps, have been a reasonable deduction to make from these experiments that hops contain no diastase, but our previous experience on the extraction of hydrolytic enzcymes from animal and vegetable tissue had shown with what tenacity these ferments are sometimes held by the cell protoplasm, and that the tissue itself will often hydrolyse by contact when its aqueous infusions have but little or no such action. As it happened, also, there was in this special case another unsuspected disturbing cause, to which we shall make reference later on.

To determine if hops can hydrolyse by contact, 5 grams of unbroken hops were added to 250 c.c. of a solution of soluble starch, containing 2.5 grams per 100 c.c., and the mixture was digested at 30° C., with the addition of a little chloroform as an antiseptic. An exactly similar control experiment for correction purposes was carried on alongside, but in this case the whole had been previously boiled to inhibit any action. At the end of three days an increased reducing power was found in the unboiled sample, after due correction, equal to 0.883 gram of CuO per 100 c.c. This is equal to 0.656 gram of maltose; so that the 5 grams of hops in three 4 days had produced 0.625 X 2.5 = 1.640 grams of sugar calculated as maltose, or a little over one-third of the weight of hops employed.

In order to show that a fermentable sugar is really produced under these circumstances, another somewhat similar experiment was made, and the hydrolysed starch solution was fermented with yeast. On the disappearance of the free maltose, the solution, which still had a considerable reducing power, was distilled, and an amount of alcohol equal to 0.24 gram per 100 c.c. was obtained. This amount of alcohol corresponds to the quantity which would be yielded by the disappearance of 0.475 gram of maltose.

It is quite possible, under well-defined conditions, to determine with considerable accuracy the relative diastatic power of different vegetable tissues. As we shall shortly lay before the Chemical Society a somewhat lengthy paper dealing, amongst other matters, with the diastase of foliage leaves, in which the method is described at length, we will not enter into any detail here, but will merely give the results of some determinations of diastatic power of several kinds of hops acting under the standard conditions. The numbers really represent the actual number of grams of maltose capable of being produced from soluble starch and amyloins respectively by 10 grams of hops, acting for forty-eight hours at 30° C. :—

Series A. Soluble starch solution. Series B. Aymloins Solution.

Grams of Maltose. Grams of Maltose.
(1) 1891. Mid Kents 7.241 9.101
(2) 1892. Mid Kents 7.955 9.309
(3) 1892. Worcester 6 8.654
(4) 1892. Bavarians 3.752 5.665

Let us consider for a moment the full significance of these numbers. Taking No. 1 as an example, we find that 10 grams of these hops are capable, under the conditions of the experiment, of producing, in 48 hours, from an excess of soluble starch, 7.241 grams of maltose; whilst from amyloins, under the same conditions, the same amount of hops has produced by hydrolysis 9.101 grams maltose. In other words, within 48 hours the hops have, in the first case, produced by hydrolysis 72 per cent. of their own weight of fermentable sugar, and, in the second case, 91 per cent.

The conditions for hydrolysis are, of course, more favour able in the experiments we have just described than they are in actual practice, owing to the very fine state of division to which the hops had been reduced ; we, therefore, repeated the experiment in a different form, using this time a beer, instead of solution of soluble starch or amyloins.

The beer had an original gravity of 1,086, and, in order to prevent any fermentation occurring during the experiment, we added to it a few drops of chloroform. One gram of unbroken hops was added to 360 c.c. of this beer ; this is at the rate of one pound of hops to the barrel. The flask was then placed at a temperature of about 28° to 30° C. The beer had originally a cupric reducing power equal to 2.995 grams of maltose per 100 c.c. At the end of seven days this had increased under the action of the hops to 3.1903 grams, an increase equal to 0.1908 gram maltose per 100 c.c., or 0.687 gram for the 360 c.c. So we see that the hops in this case, acting upon a beer under conditions which may readily occur in practice, have, within seven days, produced from the non-crystallisable starch-products of the beer an amount of maltose equal to 68.7 per cent. of their total weight.

In a barrel of beer in which three-quarters of a pound of hopping-down hops have been used, this represents a production of 8.25 oz. of fermentable sugars in seven days, a quantity more than sufficient to account for the steady after-fermentation induced by dry-hopping."
The Brewers' Guardian 1893, pages 107 - 108.
Between 0.5 and 0.75 lbs per barrel of dry hops was pretty normal in the 19th century when beers were stronger. I've seen as much as a full pound in pre-WW I London-brewed Burton Ales. So the experiment is a good representation of what might happen in the real world.

It looks proven, then, that hops contain a diastase that can convert starch into sugar. My question is this: what is the effect of the very heavy dry-hopping that takes place nowadays? Does it provoke a secondary fermentation? Has anyone noticed this?


qq said...

Yep, there's been quite a bit of discussion about hop-induced fermentation lately, they call it "hop creep" - as much for the introduction of diacetyl as anything. Mosaic is a particular culprit apparently

Peter Skelton said...


Here’s Mike Tonsmeire talking about dry hopping causing additional fermentation

A bit of speculative reasoning on my part leads me to think that this effect supports the dry hopping technique recommended by Matt Brindleson of dry hoping a few points before terminal gravity, as if your yeast is still actively fermenting then the additional sugars release by the dry hops will be fermented as part of the primary phase

This also suggests that the NE IPA technique of dry hopping at high krausen presents the same advantage

I’ve also read a few threads on probrewer where people talk about dry hopping causing diacetyl. The suggestions were that it was yeast strain related and also due to oxygen added in the actual hops. This seems to provide a better explanation, in that the additional sugar released is partially fermented by the yeast resulting in off flavours

ESBrewer said...

Here is a link to the podcast where they discuss hop induced fermentation

Mike Austin said...

I've been making cask beer at home since 1976, and I have noticed some time ago that dry hopped beer usually has a revival of fermentation in the cask.
There's no mention of this in home brewing books. Funny, that.

Anonymous said...

My guess, not based on any rigorous experimentation, is that dry hopping does revive fermentation, but it's not about any additional sugars or enzymes from the hops.

What I think happens is that dry hopping adds a lot of nucleation locations, and as a result a good deal of CO2 quickly leaves the solution that would otherwise remain - or at least exit very slowly. This type of foaming is frequently observable after the dry hops are added, and the outgassing happens much too soon after the hops are added to be the result of fermentation.

What is the result of all of this gas moving through the beer? The same thing that happens when you stir the beer -- yeast is roused back into solution, and any remaining sugars that would have been undigested are now being fermented by the roused yeast. You may also get some additional oxygen reintroduced into the solution as the additional foaming occurs and breaks up to the layer of CO2 that typically settles over the surface of beer in the fermenter.

I don't know for sure that is true, but considering the very low relative mass of hops being added, the fact that almost all of that mass is cellulose and other inert substances, and of the amount that remains most is oils, I'm deeply skeptical that fermentation is the result of anything from the hops being added. I think instead it's the physical process of gassing being triggered by a large surface area being introduced that triggers a revival of the yeast - and I would suspect you would get the same effect by adding a comparable surface area of some inert substance like hop-sized flakes of plastic or metal.

Tim said...

You can find notes referring to Brown and Morris in brewing literature:
- Sykes, The Principles and Practice of Brewing (1907), p. 207
- Chapman, Brewing (1912), p. 54
- Grenell, Die Fabrikation obergäriger Biere in Praxis und Theorie (1907), p. 210
- Schönfeld, Obergärige Biere und ihre Herstellung (1936), p. 182

and there was some additional research conducted by Janicki (1941):

J. Karanka said...

Well. That convinced me to dry hop the stock ale even if I'm not drinking it till xmas.