BrewingTechniques
Table I: Values for percent lost* for common hop varieties. +
Variety Percent Lost (%)
Cascade 50
Centennial 37
Chinook 32
Cluster 17
Crystal 49
East Kent Goldings 45
Eroica 40
Fuggle 37
Galena 15
German Spalter 45
Hallertauer (domestic) 45
Hallertauer Hersbrucker 40
Hallertauer Northern Brewer 25
Hallertauer Mittelfrueh 46
Hersbrucker (domestic) 50
Liberty 55
Mt. Hood 45
Northern Brewer (domestic) 20
Nugget 25
Perle (domestic) 15
Pride of Ringwood 44
Saazer (Czech) 50
Spalt (domestic) 50
Strisselspalt (France) 35
Styrian Goldings++ 37
Tettnang Tettnanger 42
Tettnanger (domestic) 42
Willamette 37
*At 20° C (68 F) for 6 months with no barrier packaging.
 +Data from references 5 and 8.
++Styrian Goldings are actually Fuggles grown in Yugoslavia.
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Table II: Rate constants for various values of percent lost.
Percent Lost
(%)
Rate Constant
(k)
Percent Lost
(%)
Rate Constant
(k)
Percent Lost
(%)
Rate Constant
(k)
Percent Lost
(%)
Rate Constant
(k)
10 0.00059 23 0.00145 36 0.00248 49 0.00374
11 0.00065 24 0.00152 37 0.00257 50 0.00385
12 0.00071 25 0.00160 38 0.00266 51 0.00396
13 0.00077 26 0.00167 39 0.00275 52 0.00408
14 0.00084 27 0.00175 40 0.00284 53 0.00419
15 0.00090 28 0.00183 41 0.00293 54 0.00431
16 0.00097 29 0.00190 42 0.00303 55 0.00444
17 0.00104 30 0.00198 43 0.00312 56 0.00456
18 0.00110 31 0.00206 44 0.00322 57 0.00469
19 0.00117 32 0.00214 45 0.00332 58 0.00482
20 0.00124 33 0.00222 46 0.00342 59 0.00495
21 0.00131 34 0.00231 47 0.00353 60 0.00509
22 0.00138 35 0.00239 48 0.00363 -- --
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Table III: Temperature factors used for determining rate of a-acid lost at various storage temperatures.
Temperature
(C) * (F)
Factor Temperature
(C) * (F)
Factor Temperature
(C) * (F)
Factor Temperature
(C) * (F)
Factor
20 * 68 1.000 7 * 44.6 0.548 -6 * 21.2 0.301 -19 * -2.2 0.165
19 * 66.2 0.955 6 * 42.8 0.524 -7 * 19.4 0.287 -20 * -4 0.157
18 * 64.4 0.912 5 * 41 0.500 -8 * 17.6 0.274 -21 * -5.8 0.150
17 * 62.6 0.871 4 * 39.2 0.477 -9 * 15.8 0.262 22 * -7.6 0.144
16 * 60.8 0.831 3 * 37.4 0.456 -10 * 14 0.250 -23 * -9.4 0.137
15 * 59 0.794 2 * 35.6 0 435 -11 * 12.2 0.239 -24 * -11.2 0.131
14 * 57.2 0.758 1 * 33.8 0.416 -12 * 10.4 0.228 -25 * -13 0.125
13 * 55.4 0.724 0 * 32 0.397 -13 * 8.6 0.218 -26 * -14.8 0.119
12 * 53.6 0.691 -1 * 30.2 0.379 -14 * 6.8 0.208 -27 * -16.6 0.114
11 * 51.8 0.660 -2 * 28.4 0.362 -15 * 5 0.198 -28 * -18.4 0.109
10 * 50 0.630 -3 * 26.6 0.345 -16 * 3.2 0.189 -29 * -20.2 0.104
9 * 48.2 0.602 -4 * 24.8 0.330 -17 * 1.4 0.181 -30 * -22 0.099
8 * 46.4 0.574 -5 * 23 0.315 -18 * -0.4 0.173 - -
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Table IV: Storage factors for primary storage methods.
Storage Conditions Storage Factor
Not sealed or sealed in poly bags
1*
Sealed in barrier packaging, airtight jars, but not free from oxygen
0.75**
Sealed in barrier packaging, airtight jars under vacuum or inert atmosphere such as nitrogen or carbon dioxide
0.5***
 *No Adjustment required.
**Estimated median value for median-quality storage method.
***Value derived experimentally
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Backup Math
The percent lost number is derived from the hop storage index (HSI) or is measured directly (9). These data are generally provided by hop brokers and researchers. If you know the HSI for a variety, you can calculate the percent lost by using the following formula (5):

     %Lost=log(HSI/0.25)*110

where log is the base 10 logarithm. The k value (or rate constant) is calculated according to the following formula (6):

     k = (lnAo - lnAN)/180

where ln is the natural logarithm, AO is the original a-acid value, and AN is the new a-acid value after 180 days. Now you may ask, "How do I get the original a and new a values?" As it turns out, you don't need to know. If you know the percent lost you can calculate AO and can assume any arbitrary number for AN. Calculate AO (for any value of AN) using the following formula (7):

AO = (AN*100)/(100*%Lost)

The reason AN can be any arbitrary number is that all we are really calculating here is a ratio, based on percent lost. Just make sure that when you go back to the k calculation you use the same arbitrary number you used to calculate AO.
The temperature factor (TF) is based on the research that showed that the rate of deterioration is halved for every 15 °C (27°F) drop in temperature (1). This is an exponential curve, and I simply used Excel's curve-fit algorithms to fill in the data points, using 20 °C (68°F) as the point at which no adjustment is necessary (because this is the point at which the data are measured). What I have not done is to calculate a temperature factor for values above 20 °C (values >1) because the table was getting fairly large, and you really shouldn't be storing your hops anywhere near this temperature anyway.
The storage factor (SF) is based on interpretations of the data presented in the references. A factor of 1 means no adjustment, again correlating with the measurements of percent lost.

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