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BBR Interview 3

James Spencer and I did another interview for Basic Brewing Radio, and this time it was even in person, which was a lot of fun. It deals with gravity measurements and some of the intricacies of using refractometers, and concludes with a call for additional data that will hopefully corroborate my final gravity correlation.

8 comments to BBR Interview 3

  • Ben

    Just wondering why the alcohol at fg doesn’t cause an error with the hydrometer? When i ferment a sprit wash for distillation (7kg white sugar in 25 litres), i typically get fg’s less than 1.000 (~.980). the alchohol content is much higher than beer (16+%), but i cant help wondering if the error you are seeing is not to do with the refractometer, but the hydrometer. What do you think? I have just ordered a refractometer last week so your interview with james was good timing for me. I’ll be collecting data for you.

    • Thanks for helping out, Ben.

      Alcohol in the beer does affect the specific gravity, but since SG is what we want to know anyway (whether using a hydrometer or refractometer) I wouldn’t really consider it an error. What the hydrometer reads is the FG – assuming it’s calibrated properly. A refractometer doesn’t measure SG, though; it measures the refractive index. That’s why a correlation between RI and FG is needed.

  • Ben

    How do refractometers go when measuring the likes of an imperial stout? Is the sample small enough that the dark colour has minimal effect?

    • Short answer: yes. The color of the sample doesn’t make any difference, at least not that I can see. It’s spread so thin by the cover plate that it’s almost totally transparent.

  • Gustav F

    A very useful project. I will start collecting data using both refractometer and hydrometer, but 5 samples might take a while.

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