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Way to measure density of a solution (beer/wine)

  1. Sep 9, 2015 #1
    This is a bit of a random project I am looking into. Recently a product was released called the beer bug. It measures the density of beer by tracking the weight of a submerged buoy. They calculate change in density based on changed in weight and then calculate % alcohol (ABV) from that.

    Normally specific gravity readings are taken before and after fermentation with a hydrometer. As the sugar is consumed by the yeast it changes the density. This is how you can obtain ABV.

    Both of these methods seem clunky and difficult to get a digital reading that you could track on an LED screen. Can anyone think of another way to measure density? Is there a way to measure alcohol content or sugar concentration directly?

  2. jcsd
  3. Sep 9, 2015 #2


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    Assays based on physical properties are often used when chemical methods are "awkward."
    You might look at refractive index.
  4. Sep 9, 2015 #3


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    In an industrial situation, you would use a Brixometer or refractometer to measure sugar content:


    The plain old analog hydrometer is cheap and effective. You can find digital hydrometers, but some of these devices are quite expensive:

  5. Sep 9, 2015 #4
    I'd be a little concerned that this "beer bug" might have a problem with CO2 bubbles sticking to it.
    Perhaps an automotive flex-fuel sensor with a lab-type peristaltic (or aquarium) pump could be adapted:

  6. Sep 10, 2015 #5


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    You might consider the electrical capacitance between two conductive plates in the fluid. Maybe you could use a flooded coaxial cell to eliminate external interference. Agitate the electrodes to remove CO2 bubbles.

    Water has a dielectric constant of about 80, while pure ethanol is about 24.3 at 25 °C. There will be some slight non-linearity expected due to the interaction in solution between ethanol and water. A non-linearity may be in your favor. I think it is worth investigating.
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