Tuesday, 27 March 2018

Why dry hop

I'm very grateful to Boak and Bailey for pointing me in the direction the Google Books version of the 1893 Brewers' Guardian. It's packed with interesting stuff.

Like this article on what the point of dry-hopping was. I can't say that I'd ever given it much thought. Iassumed that it was all about adding aroma to the beer. It seems that it's rather more complicated than that.

It seems that one of the points from a brewer's point of view was to bring a cask more quickly into condition. A bit like priming with sugar. In which case you wonder why only certain types of beer were dry-hopped. Though that did vary from brewery to brewery.

Boddington, for example, dry-hopped everything except Stout. Barclay Perkins dry-hopped their Pale Ales, Burton Ales and some Stouts, but never Porter or Mild Ale.


THE addition of a certain amount of dry hops to the finished beer in cask or vat is a practice which, for certain classes of beer, has been followed for so many generations that all traces of the origin of custom have been lost. Although, no doubt, the introduction of dry-hopping was due to pure empiricism, to that constant trying of experiments in all directions, and the selection of those methods which gave improved results, yet we find, as might be expected, that there are certain fundamental scientific principles underlying the practice which up to the present time have been but very imperfectly recognised.

Let us first of all inquire what are the objects which the brewer has in view in adding this small quantity of hops to his finished beer. In the first place he obtains a distinct aroma and flavour which his beer would otherwise lack; secondly, the addition of hops has a most decided antiseptic action, not only upon the beer, but also upon the cask after it is emptied; thirdly, the beer undoubtedly clarifies more rapidly than when hops are not added; and, lastly, dry-hopping induces an earlier and more persistent cask fermentation in the beer; in other words, the hops have a distinct “conditioning or freshening" influence.

It is the true explanation of that wonderful “freshening or conditioning” power of the hop which we wish to bring before you, as no sufficient reason has ever yet been given of this very remarkable function, which is perhaps the most important of any of those to which we have just called attention.

In order to satisfy yourselves of this influence of the hop, take, with all the ordinary precautions, two forcing-tray samples of a beer from skimming vessel, unions, or racking square after the primary fermentation is over. To one of these add a small quantity of hops, equivalent in amount of those used ordinarily in hopping down, and place both samples on the tray. As a rule, you will find that the sample without hops shows little or no signs of fermentation for many days, whilst that containing the hops enters into a brisk after-fermentation in a very short time, and attenuates rapidly, whilst the specific gravity of the other sample is almost stationary. This experiment is a mere imitation on a laboratory scale of what takes place under similar conditions in cask. There seem to be only three possible explanations of this action, which are as follows :—

(1) The hops contain a fermentable sugar; (2) there are, adherent to the hops, and introduced with them, certain “wild yeasts” which are capable of carrying on an after-fermentation in the beer more readily than the ordinary forms of yeast left in the beer after the primary fermentation has ceased; and (3) the hops contain a diastase: which is capable of hydrolysing the amyloins and dextrin of the beer, in this way, indirectly, supplying the yeast with a readily fermentable sugar.

We must now examine these three possible explanations of the facts in detail. As regards (I), that the effects are due to a certain amount of fermentable sugars initially present in the following experiment shows:—

Twenty grams of hops, after previous treatment with ether, were completed extracted with alcohol of 80 per cent. The aqueous residue, after distillation of this extract, was made up to 100 c.c., and examined for sugars. In the 200 mm. tube, the polariscope reading was — 1.4 divisions, and the cupric reduction was equal to 1.610 gram CuO per 100 c.c. This amount of reduction was not increased on treatment with invertase or boiling with dilute hydrochloric acid, so that neither cane-sugar nor any other carbohydrate capable of being hydrolysed  by acid was present. The optical and reducing properties point to a mixture of dextrose and levulose in the following proportions, expressed as a percentage on the amount of dry hops taken :—

Dextrose    1.55 per cent.
Levulose    2.10   ,,
Total sugars    3.65   ,,

The complete fermentability of these sugars was proved by fermenting them with yeast, and their solution gave glucosazone with phenylhydrazin acetate.

(To be continued.)

* Abridged from the Trans. Inst. Brew, Vol. VI., No. 4. By permission."
The Brewers' Guardian 1893, pages 93 - 94.
To paraphrase, there were four functions of dry hops:

  1. to add aroma
  2. kill infection in both the beer and cask
  3. help clarrification
  4. promote secondary fermentation
Why exactly did dry hops help condition beer? Well it seems from theie analysis that there are sugars present in hops. I'd have never guessed that. But what of wild yeast and diastase? You'll have to wait until next time to find out about that.

Horace Brown, in case you're wondering, was a well-respected brewing scientist.


Lee said...

Ron, I think I remember hearing one the MBAA that hop diastase has been proven to cause fermentation to restart on a small scale.

ESBrewer said...

He was ahead of his time! I recently found myself listening to some craft brewing podcast (can't remember which) where people today were studying the effects of possible secondary fermentation caused by dry hops and specifically the hypothesis that such fermentation sometimes produces diacetyl. Can't wait for the second part of the story.

Bosh said...

Also relatively recently the amount of dry hopping done in a lot of breweries has skyrocketed well beyond what I see in your historical recipes.

Kevin said...

The aspects of dry hopping mentioned above ( dry hop saturation, fermention creep and dry hop diacetyl problems ) are described in detail in this presentation -