Adjusting hop alpha acids

General Homebrew Discussion
1

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

2

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.

3

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.

4

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.

5

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

6

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.

7

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.

8

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: Hop Varieties for Beer Brewing – BeerSmith – BeerSmith™ Home Brewing Software

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.

9

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!

10

No, the reference is 20C, 68F.

11

Wow, then they really are exaggerated!  Almost meaningless to most brewers.

12

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…

13

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/

14

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(0.002220.1980.33180) = 6.24% alpha (5 F) or
future alpha = 6.4/exp(0.002220.4300.33180) = 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(0.002220.4300.5*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.  :slight_smile:

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.

15

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?

16

Yup and yup, I agree and I agree.

The IBU totally ignores alpha, so why shouldn’t we.

I was up till 11pm and now here I am up for work at 5:44am.  Icky.  But at least I don’t have to work tomorrow.  :slight_smile:

17

I’ve always read (someone confirm or correct this?) that we humans just can’t distinguish a difference of +/- 5 IBU.  Therefore,  the upshot of this should be, keep your hops in the freezer, and for years you can just act like the alpha on the label is real. Tell Beersmith to RDWHAHB.

18

I’ve heard the detectability notches are anywhere from 2-5 IBUs apart.  Personally I believe the notches spread every 3 IBUs… but I haven’t done lab analysis or blind tastings to prove this either.  Numbers like 2-3 IBUs have been thrown around in more recent years.  4-5 IBUs are the “older” numbers, if that means anything (heh… thinking back on homebrewers in 1993!).

But you’re right.  A loss of a fraction of a percent of alpha over a year or two is not going to make a huge difference, assuming we store the hops cold and well sealed.  Conversely, if not stored well, then all bets are off.

19

As to that last point, everything starts with buying from a source whose handling and storage you can trust, or all bets are off before we even get started.

20

Actually, YCH lists it on their packaging.