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refractometer question relating to og

Discussion in 'Equipment/Sanitation' started by scottab, Apr 28, 2013.

 

  1. #1
    scottab

    Well-Known Member

    Posted Apr 28, 2013
    I brewed up the brewer's best double ipa yesterday following instructions and topped off with about 2g of water when i placed in the fermenter. I took my sample reading with my fairly new refractometer. The refractometer is one of the inexpensive $30 type ones which i calibrated with distilled water. My og measured at 1.071sg / 18.4 brix. The recipe says it should be about 10 points higher. I did not take a hydrometer reading due to a time crunch. I know i topped to about 5.25g but not topped so much to make a 10 point difference, could the scale be off on a refractometer for og?
     
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  2. #2
    Yooper

    Ale's What Cures You! Staff Member  

    Posted Apr 28, 2013
    There is a refractometer/hydrometer adjustment factor that should be used. You take an OG reading with a hydrometer and one with a refractometer and then use some software to get your adjustment factor. Mine is something like .01544

    That doesn't explain a 10 point difference though. It's possible that you got a lighter reading due to the top off water.
     
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  3. #3
    scottab

    Well-Known Member

    Posted Apr 28, 2013
    So i think there are 2 issues here... i think the brewer app i used showed higher range than the kit which is why i thought 10 points sg off, the kit is 1.078-1.081 and i'm at 1.071. also i just made a 10% solution 1/4c table sugar in 2.5c of 70 degree water and my refractometer came up at 10bx but my hydrometer was 8bx... so not sure what to do to calibrate since both are correct with distilled water @ 1.000 sg
     
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  4. #4
    BroStefan

    Brewer  

    Posted Apr 28, 2013
    It helped me out when I realized the a refractometer and hydrometer are not measuring the same things, and that their principles of operation are different. A hydrometer is measuring dissolved sugar content as SG which is what matters for brewing. A refractometer measures the refraction of light through a liquid which, on a properly set up refractometer will relate to SG but is not the same thing.

    So, I trust my Hydrometer for crucial readings like pre and post boil SG and use my refractometer for quick and dirty process adjustments - is my boil off rate too high or low, for instance.

    I always take multiple refractometer readings, and the liquid needs to "fill" the space under the flip up defusing screen.

    Hydrometers will give false readings if they are not dry when the sample is put in the tube.

    Of course if the recipe is wrong...

    But that is easy to double check. Just plug the ingredients into a recipe planning program and see what you get. In my experience kits never have as many gravity points as expected
     
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