How Does A Refractometer Work?

Guy demonstrating how a refractometer works.Refractometers are an invaluable tool for any grape grower, large or small. Refractometers can let you know when its time to pick. And, they can do it with only a few drops of grape juice taken from throughout your vineyard. The alternative would be to extract enough juice from the grapes to take a reading with a wine hydrometer. This could take up to 200 berries – crushed and pressed.

For more info on refractometers and how to use them to time your grape harvest, take a look at another recent blog post, Refractometers Let You Know When To Pick!

RefractionHow a refractometer actually works is quite interesting. They can tell you what percentage of sugar is in a drop of liquid just by how much light bends or refracts as it passes through it. To see refraction in action put a straw in a glass of water. The straw in the water doesn’t seem to connect with the straw that’s out of the water. That’s refraction.

If you were to dissolve some sugar syrup in the glass of water, the straw would seem to be even more disconnected, and as you continued to dissolve more and more sugar, the “two straws” would seem to get farther and farther apart. This is the whole premise that a refractometers works upon to tell you what level of sugar is in your grapes.

Refractometer's Inside ViewA drop of grape juice is put between the refractometers prism and light-defusing plate. How much the light bends as it passes through the prism and down the barrel of the refractometer, tells you how what percentage of sugar is in the sample. As you look into the eyepiece you will be able to observe the refraction against a scale.

Because of how a refractometer works – it’s simplicity and quickness – anyone who has a vineyard of any size will find it extremely useful. With just a few random samples, you can get an accurate picture of how your grapes are doing.

Whether you have two acres or just two vines, visit our website and see the refractometers we have to offer for keeping track of your vineyard this season.
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Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.

5 thoughts on “How Does A Refractometer Work?

  1. Iv’e heard some refractometers are not accurate through their full range. So they really aren’t good for checking starting or ending gravity of beer or wine. Do you have more information on that?

  2. Todd, I have not heard of this. I will tell you that I have seen wineries use a refractometer for measuring starting and ending gravity.

  3. The alcohol produced during fermentation does throw off the “exact value” of dissolved sugar, but when comparing OG and FG, you’re really looking at relative measurements and the tefractometer works well for this. There are phone apps that will make the corrections for you when measuring the fermenting solution and thus contains ethanol.
    You can also make your own chart by taking hydrometer and tefractometer readings of the same samples.
    Then refer to this chart for the corresponding hydrometer reading in the future.

    • Al, what I have found is that a brix scale, in general, is not fine enough as compared to our tongue’s sensitivity to sweetness. You are much better off going by your own taste.

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