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Old 05-16-2010, 03:05 PM   #1
amazinglarry
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Sep 2009
new york
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Hi... Bought a refractometer a couple of weeks ago. Used for a big brew day with club members and in two successive boils afterwords and seemed to be fine. All readings were in the range of predicted gravity.

I have a brew that has been fermented for a week and got a reading of 1.036 on the refractometer which alarmed me (OG was 1060). So I checked against my hydrometer which is reading 1020. Checked the calibration with distilled water, seemed OK. Then checked another of my beers that has been sitting in fermenter for three weeks and again got a 15/16 degree differential. Site glass looks fine with no residue or scratches or cloudiness and from previous couple of brews it seemed fine, so I am confused.

If the refractometer was off from the beginning than the last 5 brew's OG this was used for were all off by 15 degrees, which I don't believe they were given the calculations before the brew. This discrepancy has only come to my attention this last week checking the FG of the last three beers I brewed.

Suggestions?

 
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Old 05-16-2010, 03:28 PM   #2
DeafSmith
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Jan 2009
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Refractometers don't accurately measure solutions with alcohol in them - that's why your OG measurements were good, but the ones after fermentation aren't. There is a way to correct the post-fermentation readings if you know the OG:
http://www.onebeer.net/refractometer.shtml

 
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Old 05-16-2010, 03:29 PM   #3
ICanHazBeer
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Apr 2010
Northern, WI
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Are you adjusting for the alcohol? When I first started using a refractometer, I watched this vid and used the spreadsheet. I now use the calculator in my brewing software.

http://morebeer.com/learn_vids/vids_refract

I've been using my hydrometer more and more when getting FG's and use the refractometer on brew day.

 
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Old 05-16-2010, 03:41 PM   #4
amazinglarry
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Sep 2009
new york
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Quote:
Originally Posted by DeafSmith View Post
Refractometers don't accurately measure solutions with alcohol in them - that's why your OG measurements were good, but the ones after fermentation aren't. There is a way to correct the post-fermentation readings if you know the OG:
http://www.onebeer.net/refractometer.shtml
Right! That makes sense, I should have thought of that. Thanks!

 
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