What is a refractometer, and how do you use one?
A refractometer measures the sugar content of a solution via the refraction of light. It performs a similar task to the hydrometer, but is far more convenient to use. Most refractometers give a reading in Brix, and some in specific gravity.
One benefit to a refractometer is that most models have an automatic temperature conversion, so samples can be taken directly from a mash or boil kettle. The second benefit is that only a very small sample is needed. A couple drops of liquid give an accurate reading. This is very helpful during all-grain brewing or during fermentation when taking multiple hydrometer-sized samples is time-consuming and ends up wasting more beer
How to Use a Refractometer
Using a refractometer is easy.
- Place several drops of the sample liquid on the angled prism.
- Seal the clear plate on top of it.
- Look through the eyepiece while pointing the refractometer at a source of direct light. (Do not look directly at the light with the naked eye!)
Refractometers aren't perfect. They're more expensive than hydrometers, and they require direct light in order to take a reading. In addition, readings taken after fermentation has started tend to read higher than they actually are. To negotiate this issue, use a calculator to make conversions.