Glossary
An optical instrument used by beekeepers to measure the moisture content of honey. The refractometer measures how light bends through a honey sample, which correlates directly to the sugar concentration and inversely to the moisture content. Honey below 18.6% moisture is considered properly ripened.
Moisture content is the single most important quality parameter for honey. Too much water (above 20%) and the honey will ferment. Too little context on when it was harvested means you are guessing about quality. The refractometer removes the guesswork by providing an instant, accurate measurement of something your senses cannot precisely detect.
A refractometer measures the refractive index, or the degree to which light bends when passing through a substance. Dissolved sugars bend light more than water does. Higher sugar concentration (lower moisture) means more light bending. The scale is calibrated specifically for honey, reading directly in percent moisture. Place a drop of honey on the prism, close the cover plate, hold up to a light source, and read the moisture percentage where the light/dark boundary crosses the scale.
The Codex Alimentarius sets the maximum moisture content for quality honey at 20%. The U.S. standard for Grade A honey is 18.6% or below. At this moisture level, the osmotic pressure is sufficient to prevent fermentation by osmophilic yeasts under normal storage conditions. Honey above 20% moisture is at significant fermentation risk and should be consumed quickly or stored refrigerated.
Before extraction: Test frames before pulling supers. If more than 20% of cells are uncapped, test the moisture to ensure it is below 18.6%. After extraction: Test the extracted honey to confirm quality before bottling. Purchased foundation stock: If buying bulk honey for resale or value-added products, test to verify claimed moisture levels.
A basic handheld honey refractometer costs to 50 from beekeeping supply companies or online retailers. Digital refractometers (more expensive, to 300) provide digital readouts but are not necessary for most beekeepers. The basic optical model is accurate, durable, and does not require batteries.
Properly calibrated honey refractometers are accurate to within plus or minus 0.5% moisture. Calibrate before use with a calibration solution or distilled water (should read 0 Brix / approximately 20% if using a honey-specific scale). Temperature affects readings; most models include an automatic temperature compensation (ATC) feature for accuracy across temperature ranges.
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