Effects of age on AA's

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Fender230

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I got some Bramling Gold from my LHBS that is from the 2006 harvest and is a bit old (the price reflected that). It was marked 7.1% but I am sort of doubting that because of the condition. Is there some sort of chart I could look at. It really doesn't matter in the end... the beer will still become bitter but it would be nice to have some sort of idea of an IBU rating.

Matt
 

mrkristofo

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From here: http://byo.com/departments/884.html

The alpha-acid levels in hops begin to tail off immediately after harvesting, and continue to decline in storage. The number quoted to you on a packet of hops purchased from a homebrew store was the alpha-acid content when the hops were tested immediately after harvest, and despite the best intentions of the retailer have been subjected to conditions that cause that level to be lower. High temperature and exposure to air will speed up the losses of alpha-acids. In hop varieties with poor storage characteristics up to 50% of the total harvest alpha-acids may be lost in 6 months stored at 70° F. A good hop will still lose 20% of its total acids under the same storage conditions. Hops should be stored in a fridge or preferably a freezer and air must be excluded from the package. This will more than half the deterioration rate of your hops. Since you have no way of predicting what the hops experienced before you bought them (remember, the inside of a UPS truck can get up to 140° F in the summer in Arizona) it is always better to buy from reputable suppliers.
That said, I have many hops stored in the freezer (8.7lbs). All are vacuum sealed, and most are in UV-tight bags. I'm not sure that I've seen a plot of alpha-acid decay over time...let me hit up my books.
 

mrkristofo

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OK, here's a solid answer, from NICKERSON, G. B. and LIKENS, S. T. (1979) J. Amer. Soc. Brew. Chem., 37, 184. (http://www.asbcnet.org/journal/abstracts/backissues/37-28.htm)

The hop storage index (HSI) is used to estimate losses of α-acids and β-acids during storage and handling. HSI is determined from the ultraviolet absorbance measured in the spectrophotometric analysis of hops. Collaborative tests of the HSI measurement gave 1.3% within-laboratory and 2.8% between-laboratory coefficients of variation. The relationship between % (α +β) lost and HSI shows some year to year variation. The slope of the equation % (α + β) lost = slope x log (HSI/constant) was 101.8, 111.3, 114.5, and 114.6 for the 1969, 1975, 1976, and 1977 crop years, respectively. The HSI has been used in evaluating varietal differences in storage, measuring permeability and antioxidant levels in *****in glands, determining hopping rates in breweries, and evaluating grower and dealer handling practices.
Particularly, they list Bramling Cross as Poor, with 40-60% alpha acids lost after 6 months at room temperature. Currently, the HSI for bramling is 35.0% lost per 6 months.
 

david_42

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Rather interesting. The USDA Named Hop Variety says the storage characteristics are good and quote the same rate of loss!

Are they positive about the type, because any form of Bramling is rare these days. The per acre yield is low.
 
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