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Error in the Hop Age tool

Hop

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Hi, I think there is a minor mistake in the Hop Age tool. It's not a bug, therefore I decided to post in this section...
This article (http://www.morebeer.com/brewingtechniques/library/backissues/issue2.1/garetz.html) claims that HSI is "a number obtained by spectrophotometric determinations of the a- and b-acids ", whilst in BeerSmith (and in the related blog article!) the HSI is supposed to indicate the percent of alfa acid lost in 6 months (%lost). This is not true, because the relation between %lost and HSI is %Lost=log(HSI/0.25)*110.
Am I right?
 
I believe the commonly used HSI is defined as it is in the program (loss over 6 months at 68 F).  However, HSI is measured using a light spectrometer method which gives a slightly different number but you can convert the spectrometer to the HSI as %lost pretty easily (as you mention).
 
Its described in some detail here as well: https://gregdwulet.wordpress.com/2015/09/04/hop-storage-index-hsi-explained/

Brad
 
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