The refractometer is the cheapest and most decisive instrument a beekeeper can buy. It measures the moisture content of honey.

Why it matters

Moisture is the property that determines whether honey ferments. Honey that is too wet spoils, and an entire batch can be lost.

Capping by the bees is a good indication, but with partly capped frames measurement is necessary — and that is the usual situation at harvest.

How it works

The instrument measures how light is refracted through the honey; that refraction depends on sugar content and therefore on moisture.

• A drop on the prism
• Read against the light
• The boundary line gives the value

Using it

• Calibrate with the supplied fluid or method before the season
• Mind the temperature; many models compensate automatically, others do not
• Take a representative sample; measuring from one cell says little
• Clean and dry the prism between readings

Where to measure

• On partly capped frames, before extracting
• In the settling tank before bottling
• On any batch of unknown origin

Measure at several points in the container; honey does not mix by itself.

What to do with a high reading

• Leave the frames in the colony longer; the bees continue to dry them
• Harvest only the capped sections
• Keep wet honey separate; do not blend it into a good batch
• Use it yourself or for mead, not for sale

What not to do

Heating to reduce moisture breaks down enzymes and raises the ageing marker. The right answer is to harvest later, not to dry afterwards.

Care

Store dry and protected, keep the prism clean, and recalibrate each season. A drifted instrument is worse than no instrument.