Refractometers are used to measure the density of sugars in malt wort, wine must or fruit juice.
Dual scaled with Brix and Specific Gravity.
Use During the grain mash, preboil and kettle out without a need for cooling a large hydrometer sample, pluck a single grape off the vine and squeeze on to the lens with a couple drops of juice and measure its sugar content for planning your harvest.
 
Calibration is recommended before every use with distilled water.
 
NOTE - Refractometers will not read correctly if alcohol is present.