Both the Brix and RI indexes need to be converted to standard specific gravity or Plato scales using a formula, as wort does not have the same reflective properties as plain sugar water. Some also use a Refractive Index (RI) scale. Most brewing refractometers measure samples in Brix, which is a scale used to measure specific gravity primarily by wine makers. More expensive models have internal light sources. On inexpensive refractometers, you hold the instrument up to a natural light source. Most refractometers use a prism and a light source to illuminate the sample. The refractometer takes advantage of this effect to measure the amount of bending (refraction) which indicates the amount of sugar in the sample. If you add sugar to your glass of water, the light will bend more. This is the same effect that glasses lenses in eyeglasses are based upon – the lenses bend the light allowing glasses to adjust the focus of an image and make it clearer to your eyes. Light bends to different degrees as it passes through different substances. The bending of the light by the water is called refraction. If you start with a glass of clear water, you will notice that the water and glass bend the light passing through it in a certain way. The main advantage over a hydrometer is the small sample size needed – typically only a few drops. It does so by sampling a small amount of liquid, and looking at its optically. How a Refractometer WorksĪ refractometer is an optical device that, like a hydrometer, measures the specific gravity of your beer or wort. I’m going to use BeerSmith as the refractometer conversion tool, as the hand calculations are fairly complex and could occupy another entire article. This week, I take a look at refractometers, how they work and how an average home brewer can use one. However, if used properly a refractometer can be a great tool to track specific gravity in place of or to supplement your hydrometer. Follow are widely used in the wine and beer industry by to track fermentation, but less commonly used by home brewers.
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