Enough different ABV amounts from different calculators

Discussion in 'General Brewing Discussions' started by Iridium, Feb 16, 2017.

  1. Iridium

    Iridium New Member

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    Hello, here a very newbie at brewing, so some doubts. One of them is related with the use of calculators in this site. When I try to know the alcohol by volume in my brewed product I obtain different numbers depending on the calculator.

    The difference is subtantial as for the same OG (Brix 9) and FG (Brix 3.8) I get 2.76 % ABV from the calculator "Alcohol by Volume" and 3.85 from "Refractometer calculator" (Wort correction factor=1).

    Maybe one or two tenths could be an acceptable difference but the amounts these calculators offer are separated more than one entire unit. I am very confused with these results. Please, could you indicate what of the two calculatores is the right one to get the ABV (and a possible explanation for the difference)?

    And yes, my brewing is a bit low in alcohol, no problem.

    (Sorry for my poor English)
     
  2. thunderwagn

    thunderwagn Well-Known Member

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    I like low alcohol brews as well. Nothing wrong with that. Brew what you like!
    Your problem most likely lies with using a refractometer to take your FG reading and the correction factor for your refractometer. I would also go by the value you are getting on the abv from the refractometer calculator since that is what you are using to take the initial readings.
    Do you happen to have a hydrometer by chance to take FG?
     
  3. Ozarks Mountain Brew

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    retractors are not very accurate for final gravities, like above I'd use a hydrometer
     
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  4. Iridium

    Iridium New Member

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    Thanks, but this is not a case of hydrometer or refractometer. The point is that if you enter the same numbers in the calculator named "Alcohol by Volume" and in "Refractometer Calculator" (wort correction factor=1), the results you get are different in ABV, but they should be the same (or similar).

    From hydrometer or from refractometer, that doesn't mind, if numbers (Plato or Brix degrees) are correct... why such differences between those two calculators?

    I agree with the better performance when measuring with hydrometers, of course.
     
  5. Yooper

    Yooper Administrator
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    Because refractometers measure the refraction of light in a sucrose (sugar) solution. It's ok for taking an OG, if you know your wort correction factor (to account for measuring maltose/maltritiose instead of sucrose), but since alcohol skews the refraction of light in a solution, the refractometer simply cannot measure the brix accurately once fermentation has begun.

    So the reading is absolutely useless as a FG, even with a wort correction factor.

    To account for this, some refractometer calculators have been developed to be used during/after fermentation. They still aren't as accurate as a hydrometer reading, but they can take the OG and the brix reading after fermentation and using a formula, guestimate the FG in brix.

    Using a refractometer after fermentation starts is just always going to be a guess. Some calculators make very close guesses, but not always.

    Due to the limitation of the refractometer to read properly once alcohol is in the solution, the easy answer is to take the OG with a refractometer if desired, but to take the FG with a calibrated hydrometer if you want an accurate FG number.
     
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  6. Iridium

    Iridium New Member

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    Yes, I'm very sorry, I did know that readings in refractometer aren't accurates at all when measuring the fermented product but I entered the numbers in the calculator "Alcohol By Volume" forgiving that basic detail. Using "Refractometer Calculator" is ok but the "Alcohol by Volume" one is not designed for refractometer measurings of final gravity.

    That was the dumb mistake, to enter the measuring from the refractometer for FG corrected wiith correction factor thinking this correction was enough. No, the factor is just useful with OG.

    So, when using refractometer for FG, the resource I have to use to know the ABV is the "Refractometer Calculator".

    (Measuring with refractometer is a quick way to obtain numbers and not waste brewing when I make little experimental batchs - just one or two liters-. When handling bigger batches I'll use the hydrometer).

    Thank you very much for your answers,
     

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