From the HBD Archive
From: roberts%studguppy@LANL.GOV (Doug Roberts @ Los Alamos National Laboratory)
Subject: Specific Gravity Different
Date: 1989-08-21 16:58:19 GMT

> The temperature correction issue should be approached with extreme caution. At
> the suggestion of my friendly dealer-guru, I performed an experiment where the
> same wort was checked with the hydrometer fresh out of the brewpot (~180), and
> at various temperatures down to the recommended 60. It turned out that the
> little correction chart badly OVERestimated the gravity at the higher
> temperatures. My advice would be to check the gravity after the wort has
> cooled, or, if the purpose of the check is to see if extracts need to be added
> to a mash wort, to ladle a little hot wort into a canning jar, set it in a bowl
> of cold water or icewater to cool down, then check the gravity.

The relationship between wort SG & temperature should be linear, if
ancient memories from my chemical engineering days serve. However, if
the wort has stratified during cooling (mine always seems to) error in
SG measurement will result if the wort isn't re-mixed prior to taking
a sample for SG. I wrote a little program for my HP-45 that takes the
SG & temperature readings, and spits out the SG corrected for 60
Fahrenheit.

I've verified that the SG variation _is_ linear with temperature by
taking subsequent readings as the wort cooled.

--Doug

================================================================
Douglas Roberts |
Los Alamos National Laboratory |When choosing between two evils,
Box 1663, MS F-602 |I always like to try the one
Los Alamos, New Mexico 87545 |I've never tried before.
(505)667-4569 |
dzzr@lanl.gov |
================================================================

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