Do you calculate alpha acid loss over time? - Home Brew Forums
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Old 01-18-2013, 03:30 AM   #1
theveganbrewer
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I was wondering how many of you calculate the loss of alpha acids in your hops over time. Do any of you even care? I have done some calculations and was surprised just how many alpha acids were lost of 6 months in optimal storage. Some varieties would throw off a final beer by 20 IBUs if not adjusted for alpha acid loss.


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Old 01-18-2013, 04:21 AM   #2
Spartan1979
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How do you know how old your hops are? Even if you know the year, you don't know when they were picked. In many cases, if you buy hops in those 1 oz Hop Union packs, how do you know what year they are?

I'm sure it matters, but I'm not sure it can be figured out.



 
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Old 01-18-2013, 04:27 AM   #3
Arrheinous
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How are you calculating/measuring AA content?

 
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Old 01-18-2013, 04:35 AM   #4
theveganbrewer
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Hops for each year are all harvested around the same time on a schedule. Most retailers list which year they are from. The hop harvest in the NW begins with low alpha, aroma varieties during the last week of August and continues through late September or early October with the higher alpha varieties.

You get the AA content off the hop bag and then calculate how much is lost based on packaging, storage temp, and days stored.
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Old 01-18-2013, 06:28 AM   #5
Arrheinous
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Ah, I wasn't sure if you were doing extractions and scientifically measuring AA content over time. I'd like to get into that kind of beer science.

 
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Old 01-18-2013, 06:36 AM   #6
BigRedHopHead
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Quote:
Originally Posted by theveganbrewer View Post
Hops for each year are all harvested around the same time on a schedule. Most retailers list which year they are from. The hop harvest in the NW begins with low alpha, aroma varieties during the last week of August and continues through late September or early October with the higher alpha varieties.

You get the AA content off the hop bag and then calculate how much is lost based on packaging, storage temp, and days stored.
Are your formulas based on evidence? Peer reviewed journal articles? Horticulturalists who spend their career on this stuff? I haven't seen much in discussion on AA loss that has been scientifically experimented on with valid and reliable formulas. This may be ignorance though...
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Old 01-18-2013, 06:37 AM   #7
HollisBT
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Bitterness calculations are pretty inaccurate to begin with, so attempting to calculate alpha loss over time is pretty pointless IMO.

It's going to vary by harvest time, the quality of the harvest, and carbonation levels.

The real solution here is to simply drink faster :cheers:

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Old 01-18-2013, 06:41 AM   #8
BigRedHopHead
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Quote:
Originally Posted by HollisBT View Post

The real solution here is to simply drink faster :cheers:
Agreed!!
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Old 01-18-2013, 07:22 AM   #9
ocluke
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Quote:
Originally Posted by BigRedHopHead View Post
Are your formulas based on evidence? Peer reviewed journal articles? Horticulturalists who spend their career on this stuff? I haven't seen much in discussion on AA loss that has been scientifically experimented on with valid and reliable formulas. This may be ignorance though...
There have been a lot of articles published in peer reviewed journals on this. The excerpt below is from an old Brewing Techniques article from 2004 that does a decent job of scratching the surface, and references for further reading of published articles are cited at the bottom.
Hops start to lose their a-acids and oils as soon as they are harvested. The rate of loss depends on the storage temperature, the amount of air present, and the hop variety. The lower the temperature, the less the hops deteriorate. It has been shown that the rate of loss halves for every 15 degrees C (27 degrees F) drop in temperature (2).

That said, I rarely use IBUs for hoppy beers, because the majority of my hop additions are at or post flame out (all calculate at zero). For hop forward beers I pay more attention to the weight, oil content and "freshness" (as calculated by a highly scientific "whiff" test) of the hops that I'm using than the calculated bitterness units. Ironically, I do pay attention to IBUs when making beers that are yeast or malt driven, and in those cases it is more to make sure that I have some bitterness structure to hold up the beer. I normally do not use an alpha acid loss calculator, but it does make sense to do so.
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Old 01-18-2013, 08:46 AM   #10
Gavagai
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Isn't there a high degree of variability in rate of AA loss between hop varieties?



 
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