Dry hopping vs. bitterness

Eureka, its time for another experiment. But not about yeast this time… Sorry! The following experiment is all about hops and their role during dry hopping and bitterness. All started with a batch of Pale Ale where I tried the first wort hopping technique and added some hops for dry hopping (100 g of 14% AA Simcoe to 22 L (5.8 gal)). And the tasting revealed an overpowering bitterness. And some really grassy notes as well. This made me wonder how the bitterness could increase to such a high level in the first place. And there are two possible explanations in my opinion: The first wort hopping technique or the dry hopping. And this experiment was to find out, if the dry hopping can increase the bitterness in some way. Some say that the bitterness only increases when the hops are boiled and the alpha acids isomerize. Others say that the bitterness can increase as well if the hops are not boiled. Lets find out how is right.

What I did was the following: I took a Vodka and diluted it down to have 400 mL of a 5% alcohol solution. I did so to have the same amount of alcohol like you would have it in an average beer. Using pure Vodka could lead to false conclusions since the higher alcohol content could extract different/less/more compounds from the hops. I then added 100 mL of the diluted Vodka to a bottle each and added some Simcoe hops to have the following hops to volume ratio: 4 g L-1, 8 g L-1, 16 g L-1 and 32 g L-1. Common rates for dry hopping are in the range of 3.9- to 7.8 g L-1 (according to Calagione Sam mentioned in “Extreme brewing”).

03/02/12: Added 14% alpha acid Simcoe hops to the four bottles according to the mass to volume ratios mentioned above. I stored the bottles at room temperature at a dark place for nearly three weeks before a tasting.

03/22/12: The tasting begun. I first start with the color differences of the liquids. It could be easily observed that a higher amount of hops lead to a darker, more orange pronounced color (Fig 1). Unfortunately, there is a light difference between the two bottles shown in Fig 1 (brighter on the left side). Nevertheless, there was a difference.

Fig 1: Hop infused Vodka, 4 g hops per liter (left), 8 g per liter (right)

Then the tasting. I have to mention first, this was by far the worst tasting ever! I advice you not to replicate these results. It was just horrible. But step by step:

4 g L-1: At the lower end of the dry hopping rates. Alcohol was easy detectable, very faint hop aroma. Maybe some hints of oranges. And the taste was just bitter. Not overpowering, but bitter.

8 g L-1: At the higher end of dry hopping rates. More intense hop aroma than the previous one. Very grassy. And the taste was just horrible. Just like eating a hop pellet. And it was definitely more bitter than the previous one as well.

16 g L-1: Extreme hoping rate 1. Orange notes in the aroma. Floral notes as well. This one is my favorite of the four concerning the aroma. And the bitterness was comparable with the one before.

32 g L-1: Extreme hoping rate 2. Floral notes, very aromatic hop aroma. The aroma is too intense for my taste. And again, the bitterness is very similar to the one before.

To conclude, the intensity of the aroma increases with the amount of the hops you add for dry hopping. I guess this is no surprise. What I am a bit more surprised is the fact, that the bitterness increases with the amount of hops as well. But only to a level of 8 g per liter of liquid. Further addition of hops does not increase the bitterness. Or at least not in a way that I could taste it. I have to mention here that I am talking about perceived bitterness not IBUs. I have no idea about the IBUs of the four samples.

Lets assume the IBUs of the different beers are the same if we consider that the IBUs originate from isomerized hops. Lets further assume that no isomerization happened during the experiment. How could we explain the increase in bitterness now? One possibility could be the extraction of compounds from the hops by the alcohol present. This would imply that further compound(s) in the hops can increase the bittering sensation. And basically lead to the conclusion that a higher amount of dry hops can increase the bitterness. Not the IBUs but the perceived bitterness.

I assumed that hops for dry hopping could maybe just add a bit of bitterness. But here we are talking about huge impacts. The liquids with the highest amounts of hops tasted like liquid hop pellets… I am still not really convinced here. Maybe this is just something happening only in the used Vodka-based liquids. It is therefore advisable to replicate these results using a fermented barley-based liquid. However, I conclude that a higher amount of hops in a Vodka-based liquid leads to an increasing perceived bitterness (can’t tell if the IBUs increased).

Please let me know if anyone out there has an idea what happened here or if you obtained different/same results as well. Cheers and stay tuned for further post.


15 thoughts on “Dry hopping vs. bitterness

  1. Interessantes Experiment wie ich finde.
    Eine Erklärung könnte ich gegebenfalls beitragen. Während der Produktion der Hopfenpellets werden diese gepresst. Dabei entsteht so stark relevante Wärme, dass hier aktiv gekühlt werden muss. Ein Teil/ im inneren des Pellets könnte trotzdem relativ stark erhitzt werden. Dabei findet eine Teil-Isomerisation der Alpha-Säuren statt. Dadurch kommt beim Dryhoppen diese Bitterness in den Sud. Könnte sein 😉

    • Hi Fabian, please let my translate your great idea in English first. Fabian mentioned that during the compressing step in the production of pellets, the pellets get relatively warm and you have to cool them actively. He then assumes that some parts of the hops might get warm enough to have isomerization happening. These isomerized alpha-acids then could be extracted during the dry hopping step and thus leading to an increase in bitterness.

      Fabian your idea seems to make a lot of sense to me and imply an increase in IBUs. And very easy to test: One way would be to measure the IBU’s in the liquids. I could get access to a photometer somehow. On the other hand, using whole hops. If the bitterness increases there as well… you get the point, right? I shall repeat the experiment with a beer-base and use pellets and whole hops side by side. And then measure the IBUs as well. Thank you very much Fabian for your great idea. Cheers! Samuel

      (Fabian, bitte verzeih mir dass ich alles hier auf English antworte. Es geht mir nur darum, dass andere mitlesen können. Es ist aber überhaupt kein Problem für mich, wenn du mir Kommentare in Deutsch schreibst. Ich werde sie jeweils kurz übersetzen und dann in English antworten. Danke für Deinen Kommentar, grüsse Samuel)

      • Hi Samuel,
        Its maybe a good training to formulate my arguments in english. Im realy out of training since school is finished and my study works very well with german so far 😉

        Your new build of experiment sounds great. As a base liquid you can ferment a
        hopless gyle. Just get a part of your next beer before adding hops.
        Then try dried or maybe better fresh full hops if you can get.

        Good luck, im realy interested in all of your tests and brew´s,

        Ps. Maybe translate it for other users anyway 😉 😉

  2. Hi Fabian,
    I will think about an experiment and I see no need to translate your comment. As I have fresh hops growing in my garden (East Kent Goldings, Hallertauer, Northern Brewer and Cascade), they seem very suitable to be used for such an experiment since I have no idea about the alpha acids of these. Can’t wait to brew a Harvest Ale made with freshly harvested Cascade hops… 🙂

    Cheers and thanks for commenting,

  3. You can find vodka made from grain spirits. Do you know which variety you used? The two most common types are grain spirits and potato based. I think it’s rye and wheat that are used. They are not barley based, though.

  4. I recently brewed a beer with zero hops in the boil, but dry-hopped for 4 days with 6 oz (2 oz each) of high-alpha hops (Simcoe, Summit and Apollo). Only the Apollo were pellets. This beer turned out quite bitter and with the same kind of bitterness you would expect from hops in the boil.

    • The main goal here was to see if one can extract bitterness with excessive dry hoping. And to test that one has to go to excessive ratio. Otherwise, you might not see an effect.

  5. Hi,

    Interesting stuff. Have you had the chance to continue with this line of research?

    I just read a 2014 thesis by Parkin where she studied the effects of dry hopping on perceived bitterness. The study found a link and stated: “While both humulinones and polyphenols may contribute significantly and linearly to the BU and sensory bitterness it is the former that is potentially responsible for the majority of the increase”. Interestingly, while perceived bitterness increased during dry hopping, Parkin found that the concentration of iso-alpha acids actually decreased during dry hopping.

    The study can be found here: https://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/51185/ParkinEllenJ2015.pdf


  6. beta-acids do not require isomerization. they are known to add bitterness through oxidization. your test bottles seem to be mostly empty; and in that empty space is oxygen. this is why you will get more bitterness after a somewhat long dry hop, post-fermentation. the CO2 blanket is much weaker; oxygen will sneak in. i suggest you redo the test with full bottles, with no air headspace. with much much less oxidization, you ought to get much less bitter results.

    • True, oxygen will have an impact. As the years past since these experiments, I can tell from commercial experience now, that an increase of dry hop additions do increase the perceived bitterness. And we are talking real beer, closed fermentation tanks with CO2 blankets. One reasonable explanation for me is that an increase of hops also increase the likelihood of extracting more “plant” material into beer. Like tannins and what-not. Which all lead to an increase of perceived bitterness.

  7. I have noticed this effect in home-brewed IPAs. The grassy taste is probably from the cones themselves (happens often when you dry hop with fresh hops and use too many or leave them in too long). The bitterness could just be the hop remains. Did you use a very fine filter to remove as much of the hops remains as possible? As you point out, hop pellets taste extremely bitter, even though they have not been isomerized.

    • Agree. I suppose this is something I take-up quite often with IPAs out there. To me, it looks like a lot of hops were added and in the end, you extract plant material into the beer – which comes accross as being bitter/grassy. Flavours which I do not really like. As for the filter, I cannot recall what I used for these trial experiments six years ago… 🙂

Comments are closed.