second guessing my refractometer

Discussion in 'General Brewing Discussions' started by oliver, Jun 21, 2017.

  1. oliver

    oliver Well-Known Member

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    Need help, I have a dual scale refractometer, and I read an article online that claims that I shouldn't read the SG side, only the Brix side. so I went in and converted all my SGs to Brix based on a photo I took inside my refractometer. My efficiencies went through the roof.

    the model I have is RSG-32ATC, and here's a picture of the inside ...

    [​IMG]

    Should I be reading the Plato Brix side? Or the SG side?
     
  2. Mark D Pirate

    Mark D Pirate Well-Known Member

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    How do the readings compare to a trusted hydrometer ? I'd be sticking with SG unless I had very good reason not to
     
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  3. Trialben

    Trialben Well-Known Member

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    Spot on Mark I'd get a back up reading with a hydrometer then if the two differ go from there.
     
  4. CRUNK

    CRUNK Well-Known Member

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    I have 2 hydrometers, and a refractometer for a trifecta, i like to be sure, mechanical failures can happen all to easily, and it usually happens at the most inconvenient time.
     
  5. Myndflyte

    Myndflyte Active Member

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  6. oliver

    oliver Well-Known Member

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    Brewersfriend said I believe said don't trust the SG side because Brix and SG are not linear...

    the only reason I'm opposed to checking with a hydrometer is because I make such little batches already, I hate wasting a whole tube of beer....

    Using my hydrometer would be a good way of checking, I guess I could be super sanitary and just repitch my sample after brewday.

    any other concerns about refractometer readings?
     
  7. Nosybear

    Nosybear Well-Known Member

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    Here's the fancy formula for converting: Multiply brix times 4 to get gravity points. The difference is Brix is based on the assumption that the gravity difference is dissolved sucrose, which wort is not. Yes, it's not linear but at our scale does that point or two at the top and bottom end of the scale make a difference? I've brewed a lot of batches and cross-checked my hydrometer and refractometer numerous times. Guess what? The difference is a point or two at best if I cool the refractometer sample to the same temperature as the hydrometer sample. I've retired my hydrometer on brew day. I went out and found a Brix vs. SG table and charted it:

    upload_2017-6-21_8-45-27.png

    The line is very subtly curved which is why I put the dotted trendline (linear regression for the stats geeks out there) in the chart. The curve is so subtle you can't see it without the linear reference. This backs up my supposition: If both instruments are calibrated and reasonably accurate, you can assume there is no difference in the readings for Brix and SG, even if the scales are approximated as linear. Eyeballing the error, it looks like about 0.5° Brix at either end.

    Yep, I do this stuff every day in my day job.
     
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  8. oliver

    oliver Well-Known Member

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    applause for @Nosybear .

    So, I shouldn't worry about it.. OK.

    BUT, that changes my efficiencies and ABVs like crazy still.

    efficiencies have jumped like 10% when reading Brix, and ABV jumps a whole percent. My last two brews were clocked at 8% based on specific gravity and advanced formula, now both are at 9% when using Brix to start and specific gravity for final, (and advanced equation)
     
  9. Nosybear

    Nosybear Well-Known Member

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    The only way it's changing efficiencies and ABV by the amounts you mention is if either one (or both) of the instruments are not correctly calibrated, are defective or you're taking a reading incorrectly. There's not enough difference in the scales to make up for a 10% difference. Efficiency is not a function of the scale you use, it's the measure of the amounts of solids you got to the theoretical content of the grain. Check the instruments first - there shouldn't be that much difference in the outcomes.
     
  10. Ozarks Mountain Brew

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    you cant measure final gravity with a refractometer, the alcohol messes up the reading, use it to start a beginning but use the hydrometer for the final, thats the only way to be accurate
     
  11. HighVoltageMan!

    HighVoltageMan! Well-Known Member

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    Absolutely. I have used a refractometer for years during brew day and a hydrometer for final gravity and I have never had a reason to question the accuracy of the refractometer on brew day. But as soon as I pitch the yeast, I will go back to the old school way because I have yet to find a calculator that works with a refractometer reading once alcohol is in solution.

    The refractometer has change the way I brew my beer. I check for gravity the entire brew, from mash tun to boil. As the conversion in the mash progresses, the line on the refractometer becomes more distinct and you get a good feel when conversion is complete. I never boil for volume, only for gravity. I have checked the refractometer against a hydrometer and they are always in agreement. But they do occasionally need to calibrated with distilled water.

    Oliver: How did you take that picture of the refractometer display?
     
  12. KC

    KC Active Member

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  13. oliver

    oliver Well-Known Member

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    UPDATE! And back on topic....

    I made an impromptu extract batch today with a friend. Aiming for 1070sg, we tested the wort both with a hydrometer and refractometer.

    The refractometer read 16.6 brix, or about 1065 when using the side by side scale inside the glass. The hydrometer reads 1068 in the wort. A quick calculator test from brix to sg results in 1068. Boom, the SG is useless.

    Brix is the way to go in the refractometer.
     
  14. oliver

    oliver Well-Known Member

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    I held the refractometer loop up to my iPhone lens, point towards the sun, autofocus, ta-da
     
  15. Nosybear

    Nosybear Well-Known Member

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    You didn't mention chilling the hydrometer sample or the refractometer sample. And I hate to bring this up but the scale you're using is not the issue. If the refractometer is of any quality whatever, the SG and Brix scales have been calibrated with each other. 16.6 Brix equates to 1.068 SG. In the picture above, the Brix is 23.3, the SG 1.091. That's wrong according to the Brix table I reference: It should be 1.098. The problem isn't whether to use Brix of SG, it's a faulty scale in the refractometer.

    I've stopped measuring with the hydrometer on brew day because, when I cool the refractometer sample, I generally wind up with 1 to 2 degrees of SG between the two. That's within reading error on my hydrometer so I just go with what the refractometer says. Even the three degree error you mentioned is not that significant in homebrewing. Your call, though. I like the convenience and smaller sample size.
     
  16. Trialben

    Trialben Well-Known Member

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    This is what put me off getting one too much involved.
     
  17. Mark D Pirate

    Mark D Pirate Well-Known Member

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    I will be buying one for brewday readings , a drop of wort cools much more quickly than the 100 ml I need for my hydro tube so can get an almost instant reading and adjust hopping / sparge volumes on the fly
     
  18. HighVoltageMan!

    HighVoltageMan! Well-Known Member

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    Cool!
     
  19. Nosybear

    Nosybear Well-Known Member

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    There's an article in Zymurgy this month on how to use one throughout the brewing process. Talk about your synchronicity! In any case, they're great tools for brew day. I'm still not sold on them during the process but, after I've had a chance to digest the article, could be. It might be interesting to know how fermentation is progressing and CO2 doesn't affect their readings by much.
     
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  20. BoomerBrian

    BoomerBrian Active Member

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    I figured out the correction for my refractometer and use it all of the time to measure FG. Close enough for me.
     

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