Author Topic: Adjusting hop alpha acids  (Read 783 times)

Offline Andor

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Adjusting hop alpha acids
« on: March 27, 2018, 11:22:43 PM »
I've always just went with what the hops aa's were when I bought them but planning for a brew today I plugged each hop into beersmiths hop tool and it resulted in a pretty big difference in ibus. All hops are 2016 harvest stored in food saver or original package  in freezer. Has the decline in aa's been proven to be accurate given modern storage processes? Beersmith asked hop storage index, temp, and package


What are you guys doing? Adjusting or leaving as is?  I realize either way is a guess, I'm just looking for the best guess

Offline Robert

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Re: Adjusting hop alpha acids
« Reply #1 on: March 27, 2018, 11:31:35 PM »
HSI is never listed on packages for homebrewers.   IBU is a mythical WAG unless you have a professional lab and a large number of trials to calibrate your system. Then it's almost SWAG.  Go on experience, and adjust recipe based on evidence from your taste buds.
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Offline klickitat jim

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Re: Adjusting hop alpha acids
« Reply #2 on: March 27, 2018, 11:47:19 PM »
Since I don't have customers whining about minor differences in perceived bitterness, and I don't have a label investment showing IBUs, I don't adjust at all from lot to lot or year to year. I only use IBU estimate for ballparking a new recipe and adjust from there. It's a stake in the ground and that's it. There's way too many factors effecting perceived bitterness to get all microscopic about IBU. I actually think more and more pros will be going away from numbers and just describing the beer with words. Some pros, like Ben at Breakside, is even getting away from saying which varietals he uses because they drift too much. They are using their noses instead and shooting for a sensory target.

Offline dmtaylor

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Re: Adjusting hop alpha acids
« Reply #3 on: March 28, 2018, 12:36:54 AM »
In my experience, I don't find hops to lose as much alpha acid over time as some sources suggest.  Maybe 10% per year.  Maybe it's dependent on the particular strain, but if so, I don't understand why because it's all the same chemical family.
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Offline yso191

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Re: Adjusting hop alpha acids
« Reply #4 on: March 28, 2018, 05:16:20 AM »
In my experience, I don't find hops to lose as much alpha acid over time as some sources suggest.  Maybe 10% per year.  Maybe it's dependent on the particular strain, but if so, I don't understand why because it's all the same chemical family.

I don't understand the mechanism either, but I do know it varies widely by hop variety.  Here is an excellent write-up on the topic.  Scroll down 2/3 of the way and it will list common varieties with typical losses: https://www.morebeer.com/articles/storing_hops_properly
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Offline dmtaylor

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Re: Adjusting hop alpha acids
« Reply #5 on: March 28, 2018, 10:53:33 AM »
In my experience, I don't find hops to lose as much alpha acid over time as some sources suggest.  Maybe 10% per year.  Maybe it's dependent on the particular strain, but if so, I don't understand why because it's all the same chemical family.

I don't understand the mechanism either, but I do know it varies widely by hop variety.  Here is an excellent write-up on the topic.  Scroll down 2/3 of the way and it will list common varieties with typical losses: https://www.morebeer.com/articles/storing_hops_properly

Yeah... I have my doubts as to the accuracy.  If we assume that our well stored hops lose 0.1% alpha every 37 days, your IBUs will be WAY off after say 296 days after they'd supposedly lost 0.8%.  That's way off.  I have used old hops that were 2-3 years old MANY times and they only ever lose maybe 0.5% or something like that based on real taste.  If you go by the calc, your beer WILL be too bitter.  The calcs are conservative.  Just like mrmalty.com.  Figure these calculators double all their results, cut them in half, and you'll be alright.
Dave

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Offline mabrungard

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Re: Adjusting hop alpha acids
« Reply #6 on: March 28, 2018, 12:12:01 PM »
Since I store my hops in the freezer, I also ignore alpha loss calculations. Those alpha loss calculations do seem to be too conservative based on my experience.
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Offline yso191

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Re: Adjusting hop alpha acids
« Reply #7 on: March 28, 2018, 02:26:46 PM »
And we really don't have a choice do we?  Since they don't list HSI (or oils, which IMO is way more important) it's a guessing game.

I ignore alpha losses also.  But I also only use the freshest hops available.  I throw away unused hops when the new harvest is done.  I'm also thinking one should stay away from varieties that degrade quickly (Cascade, CTZ, etc) and opt for varieties that degrade more slowly (Galena, Nugget, etc).  Here is a useful website, just click on a hop and it will tell you average HSI for that variety: http://beersmith.com/hop-list/

As has been mentioned, nitrogen flushing, mylar bags and especially cold storage are key.

A final point.  I know (at least at BSG, and I assume other hop processing companies) prioritize processing the hops that tend to lose alpha the quickest, so as to get them into the best state as rapidly as possible.
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Offline Robert

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Re: Adjusting hop alpha acids
« Reply #8 on: March 28, 2018, 05:28:59 PM »
Since I store my hops in the freezer, I also ignore alpha loss calculations. Those alpha loss calculations do seem to be too conservative based on my experience.
Don't the figures for alpha loss assume storage at 0°C?  It would seem a home freezer at 0°F (-18°C) offers a real advantage!
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Offline hopfenundmalz

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Re: Adjusting hop alpha acids
« Reply #9 on: March 28, 2018, 07:44:41 PM »
Since I store my hops in the freezer, I also ignore alpha loss calculations. Those alpha loss calculations do seem to be too conservative based on my experience.
Don't the figures for alpha loss assume storage at 0°C?  It would seem a home freezer at 0°F (-18°C) offers a real advantage!
No, the reference is 20C, 68F.
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Offline Robert

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Re: Adjusting hop alpha acids
« Reply #10 on: March 28, 2018, 08:11:13 PM »
Since I store my hops in the freezer, I also ignore alpha loss calculations. Those alpha loss calculations do seem to be too conservative based on my experience.
Don't the figures for alpha loss assume storage at 0°C?  It would seem a home freezer at 0°F (-18°C) offers a real advantage!
No, the reference is 20C, 68F.
Wow, then they really are exaggerated!   Almost meaningless to most brewers.
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Offline dmtaylor

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Re: Adjusting hop alpha acids
« Reply #11 on: March 28, 2018, 08:19:09 PM »
Since I store my hops in the freezer, I also ignore alpha loss calculations. Those alpha loss calculations do seem to be too conservative based on my experience.
Don't the figures for alpha loss assume storage at 0°C?  It would seem a home freezer at 0°F (-18°C) offers a real advantage!
No, the reference is 20C, 68F.

I haven't checked all the references so carefully, but if true and the calculators are based on 20 C, but most brewers are storing the hops at 0 C, then per Arrhenius general rule of thumb where chemical reaction rates double for each 10 C rise, we should expect degradation to occur at approximately 25% (0.5 squared) at 0 C compared with whatever the calc spits out.  This seems to correspond with our experiences pretty well -- I said 1/2 but maybe it really is 1/4 as much loss as "they" say.  I'm pretty busy at the moment (so why the hell am I writing this??) but if I remember I will check more references tonight or this weekend....
Dave

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Offline Andor

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Re: Adjusting hop alpha acids
« Reply #12 on: March 28, 2018, 08:46:45 PM »
Since I store my hops in the freezer, I also ignore alpha loss calculations. Those alpha loss calculations do seem to be too conservative based on my experience.
Don't the figures for alpha loss assume storage at 0°C?  It would seem a home freezer at 0°F (-18°C) offers a real advantage!
No, the reference is 20C, 68F.

I haven't checked all the references so carefully, but if true and the calculators are based on 20 C, but most brewers are storing the hops at 0 C, then per Arrhenius general rule of thumb where chemical reaction rates double for each 10 C rise, we should expect degradation to occur at approximately 25% (0.5 squared) at 0 C compared with whatever the calc spits out.  This seems to correspond with our experiences pretty well -- I said 1/2 but maybe it really is 1/4 as much loss as "they" say.  I'm pretty busy at the moment (so why the hell am I writing this??) but if I remember I will check more references tonight or this weekend....


Hop storage numbers are 6 month at 20c from what ive seen but beersmith adjusts based on the the actual storage temp and the package. At 20c most hops I've looked at lose at  25% of their aa after 6 moths.  With beer smiths numbers it showed about a loss 3 alpha acid
After 18 months

http://beersmith.com/blog/2008/04/15/brewing-hops-storage-preserving-precious-hops/

Offline dmtaylor

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Re: Adjusting hop alpha acids
« Reply #13 on: March 29, 2018, 04:12:31 AM »
Okay......... I've spent a couple more hours pondering the ancient Garetz article.

My thoughts:

The Garetz-Nickerson formulae are indeed based on Arrhenius as I mentioned previously, but they claim that degradation reaction rate doubles for every 15 C, not every 10 C as many other reactions do and that I mentioned before.  Okay.  I can accept that.

The data and equations were finalized in about 1993.  I believe hop harvest and storage technology has come a little ways since 1993.  As such, I propose that the Storage Factor SF from Table IV might be as low as 0.25, or for fun let's say it is 0.33, i.e., a little bit better than the 0.5 minimum possible back in 1993.

Digging a little deeper and pulling up some old Nickerson references, it appears both alpha and beta acid losses are accounted for here, not just alpha.  So, part of the loss I think is beta.  But for conservatism, we can ignore beta and assume it's all alpha that is lost.  Alright.

Now for average hops' sake, I won't assume every hop is as bad as Cascade for storability per Table I (Cascade was said to be determined to lose 50% alpha and beta at 68 F over 180 days).  Let's go with an average joe hop that loses an assumed 33% alpha (ignoring beta) after 180 days.  This is what Garetz calls "%Lost".

From %Lost, go to Table II (which I verified accurate), and you get a rate constant k of 0.00222 for 33% lost for average-joe hop.

Now, storage temperature..... I know I have my freezer set at exactly 5 F.  Others might have their hops stored in the refrigerator at say 35 F.  Let's see how that computes..... For 5 F, Table III (also verified accurate) says the Temperature Factor TF is 0.198.  And at 35 F, TF would be about 0.430.  Hmm.  Let's see what effect that has....

Pumping all the numbers into the bastardized Arrhenius equation, let's say for average-joe hop of initial 6.4% alpha, stored at 5 F or 35 F for 180 days, the maths look like this:

future alpha = 6.4/exp(0.00222*0.198*0.33*180) = 6.24% alpha (5 F) or
future alpha = 6.4/exp(0.00222*0.430*0.33*180) = 6.05% alpha (35 F)

So, whether stored in the fridge or in the freezer, I figure we've lost at most 0.35% alpha for average-joe hop after 6 months.

This all assumes a vacuum or nitrogen sealed pack, which I think most of us are doing these days.  If not, it would be beneficial.

The same hop back in 1993 might see a loss more towards... 6.4/exp(0.00222*0.430*0.5*180) = 5.87% alpha

which I'm saying would be due to hop growers back in the old days not doing as good a job of packaging hops early after harvest, and the less stellar packaging materials and methods compared to today.

What does all this mean?

To me it means that the freezer is still better than the fridge, but in either case, let's keep that oxygen out of there if we can, m-kay?  I haven't run a lot more numbers but you can see that if you are storing your hops as well as humanly possible, you're really NOT going to lose much alpha at all over time, and they'll keep for YEARS in either the fridge (pretty good) or freezer (awesome).

And there now you have the results of my geekiness to ponder for your enjoyment.  :)

EDIT: And I still don't know exactly what makes different hop varieties SO very different on Table I.  I don't really believe the variance can be so much, from 15% loss with one hop to 50% for another.  I'll bet those percentages are good to about a half a sig fig --  they seem pretty rough -- but I don't have the source data to know that for a fact either.
« Last Edit: March 29, 2018, 04:24:20 AM by dmtaylor »
Dave

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Offline Robert

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Re: Adjusting hop alpha acids
« Reply #14 on: March 29, 2018, 04:38:59 AM »
Dave, two things:

(1) I don't think you _can_ really ignore beta.  It oxidizes to soluble form at essentially the same rate that alpha is lost, so it offsets alpha loss to a significant degree.  (This explains how landrace varieties were selected: they exhibit near 1:1 alpha:beta and so had _apparently_ better storage stability.)

(2) Why are we still awake and on this forum, man?
Rob Stein
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