# Hop utilisation changes with gravity - Does it really?



## danestead (30/7/14)

I've noticed a lot of late, particularly amongst Kits and bits type brewing, that you want to boil your hops in a certain gravity of wort to get the best utilisation out of your hops.

I also know that brewing software follows that belief and adjusts the calculated IBUs based on boil/wort gravity.

Is this really true though? I know that in John Palmers 'How to Brew' he goes on to say that the gravity affects your hop utilisation however a few years ago there was a podcast (which I'm unable to access atm) saying the contrary.

Both John Palmer and Zamil alphabet were saying that it is now scientifically proven that wort gravity does NOT affect the hop utilisation.

I am just wondering why I haven't seen this topic come up here although it is very often stated that you want a certain gravity for best hop utilisation.

Has anyone looked further into this and done some testing at all or have anything further to add?


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## ManVsBeer (30/7/14)

I was reading the other day somewhere that the effect of wort gravity on hop utilisation should be applied to bittering hops and only has a negligible effect on flavour and aroma additions. More food for thought.


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## danestead (30/7/14)

ManVsBeer said:


> I was reading the other day somewhere that the effect of wort gravity on hop utilisation should be applied to bittering hops and only has a negligible effect on flavour and aroma additions. More food for thought.


You know that may be plausible because I have also read that Palmer and Jamil were possibly saying that break material can affect the utilisation. That could explain why bittering additions are affected more (if you are pitching hop additions prior to the majority of the hot break to be over).


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## ManVsBeer (30/7/14)

I believe this is a fairly important topic not just for K & B brewers, but also for people like myself who are into into to AG high gravity wort boiling and dilution in the fermenter. The numbers being thrown around are 20 - 30% extra hop additions or 10% per 10 points over 1.050.

Currently I add an extra 30% if my software doesn't come up with a result much over the highest IBU for style. I was thinking for my next batch, 30% extra hops for bittering and 10% extra for flavour and aroma.

This is all well and good and will brew a good beer, but it would be nice to know how to actually have a beer taste as it was intended from the recipe.

Maybe your original post is correct and we shouldn't be trying to alter anything....


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## Ross (30/7/14)

Commercially & at home I've always adjusted for gravity & the taste (bitterness) has always been as expected. What the measured figures are i have no idea.

cheers....


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## danestead (30/7/14)

Ross said:


> Commercially & at home I've always adjusted for gravity & the taste (bitterness) has always been as expected. What the measured figures are i have no idea.
> 
> cheers....


When you say you've always adjusted for gravity, do you mean you have let your brewing software do it automatically or you have done manual calculations?


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## dent (30/7/14)

To me, it is a bit of a moot point - you're pretty much always wanting more bitterness to go with the bigger beers anyhow. Plus that point of possible balance gets wider as the beers get bigger - every individual IBU gets less and less important. 

When you get to a 1.100 beer, the calculations go out the window. Could be 50g of Magnum @ 90 minutes for 20 litres, or 100g, both would be acceptable.

Perceived bitterness is what counts in the end. Though I guess that doesn't answer the original question.


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## danestead (30/7/14)

dent said:


> To me, it is a bit of a moot point - you're pretty much always wanting more bitterness to go with the bigger beers anyhow. Plus that point of possible balance gets wider as the beers get bigger - every individual IBU gets less and less important.
> 
> When you get to a 1.100 beer, the calculations go out the window. Could be 50g of Magnum @ 90 minutes for 20 litres, or 100g, both would be acceptable.
> 
> Perceived bitterness is what counts in the end. Though I guess that doesn't answer the original question.


I believe you do have a point zig, which as you said isnt really to do with the original question however if we take some of john Palmers figures we will see what we come up with in your scenario.

His utilisation figures for 1.050 and 1.070 are 0.231 and 0.193 for a 60min addition. With a little maths we see that they are pretty much 20% different. If we were doing, say an ipa style with 1:1 bu:gu we would be using 50 Ibus for the 1.050 brew and 70 ibus for the 1.070 brew assuming no effect from differing hop utilisations. If we do take into consideration palmers 'original thoughts on utilisation' we would need 20% more hops to achieve 70 ibus. This is kind of like saying 84 ibus worth of hops if you calculated it based on the 1.050 utilisation rate.

Would you taste the difference between 70 and 84 ibus? I don't know however I think there is enough of a difference there to at least think about it.

Anyway, still trying to see what others think and whether anyone has compiled any data.


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## manticle (30/7/14)

If you listen/read further, you'll see that the data that the gravity/ibu measurements were originally based on show empirically that there is a correlation between wort gravity and utilisation.

However recent experiments have demonstrated/suggested that it is not the amount of sugar in lquid that is responsible. The equations are not disproven but the assumed causal factor has been put under the spotlight.


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## technobabble66 (31/7/14)

This is one paper indicating a change in amounts of iso-alpha-acids in boiled wort resulting from varying temp, pH, OG, Mg/Ca/SO4/Cl.




Degradation of Iso-α-Acids During Wort Boiling 




*This paper looks solely at the iso-alpha-acid LOSSES during wort boiling, not the extraction/conversion of alpha acids, as per the OP's question.*
So this paper is slightly Off Topic, however i thought it was interesting, and is still related as it relates to the impact of OG on the Iso-alpha-acids in the finished beer.

I think what it is basically referring to is that regardless of your extraction rate of Alpha Acids and your rate of conversion to Iso-alpha-acids (the bitter ones we perceive), there is also a "problem" with these iso-alpha-acids being degraded into other things - generally compounds considered undesirable.
I'd point out that this "undesirable" tag may or may not be accurate - i think its basically looking at hops for bittering, and hence the commercial interest of maximising the smooth bitterness from hops. The "undesirable" tag also depends heavily on the opinion of iso-co-humulone (one of the prominent degradation products) causing more harsh bitterness, something that is refuted in more recent studies. This is also working on the simplistic assumption that all these degradation products add nothing to flavour other than good or bad bittering, and doesn't consider the impact of these variables on the hops oils - where lots of the flavour comes from.
So basically, the losses of Iso-alpha-acids will result in a decrease in the yield of bitterness per gram of hops, [but may provide unidentified benefits (or negatives) to do with flavour].

*The basic summary of the findings were that higher temps, higher OG, lower pH, and Mineral salts (namely CaCl & MgCl, not CaSO4 so much) all increase iso-alpha-acid losses.*
In particular (Figure 4): At 1.040, there was a 10% loss of iso-alpha-acids, at 1.074 there was a 50% loss.
The rate of loss was fairly linear in relation to OG changes.
Depends on whether you want those degradation products or not, but in terms of (smooth) bittering, this alone would suggest OG makes a big difference in the bittering yield of the hops in the finished beer.


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## ManVsBeer (31/7/14)

manticle said:


> However recent experiments have demonstrated/suggested that it is not the amount of sugar in lquid that is responsible. The equations are not disproven but the assumed causal factor has been put under the spotlight.


I assume that is the information techno was posting??


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