Glossary
Refractometer
An optical instrument that infers dissolved sugar from how much a few drops of liquid bend light.
Its advantage is sample size: a couple of drops rather than a trial jar, which makes it practical to check gravity repeatedly through a brew day without losing volume.
Its limitation is that ethanol has a different refractive index from water, so once fermentation has begun the raw reading is wrong. Post-fermentation readings must be run through a correction formula, and those formulas are approximations that disagree with each other at high alcohol levels.
Related
- Hydrometer — The instrument unaffected by alcohol.
More vocabulary
Beer engine · Coolship · Foeder · Hydrometer · Kettle · Lauter tun · Mash tun · Sparkler
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Last reviewed 2026-08-16.