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Honey moisture content: refractometer check

A drop on the prism, a reading on the water scale: enter it here to see whether your honey will keep, whether it may be sold under the UK Honey Regulations, and what blending two batches would give.

% water
Calibrated refractometer, instrument and honey at room temperature. Sample several frames, including the uncapped cells at the edges.
Honey
Blending two batches (optional)
kg
%
kg
%

Verdict

17.5%

Ripe: it will keep

At 17.5 %, the honey is dry enough to keep without fermenting. You can jar it.

Blend: 45 kg at 17.7 % water.

How it is calculated

The thresholds

Water contentWhat it means
Below 17 %No fermentation.
17 to 18 %The keeping target: no fermentation unless yeasts are very numerous.
Over 18 %, up to 20 %Legal, but from about 19 % there is a definite risk of fermentation in store (froth, sour smell, sharp taste), higher once the honey sets.
Over 20 %Over the legal limit for most honey: it cannot be sold as honey. Yeasts multiply freely.
Up to 23 %Legal limit for heather (Calluna) honey and for baker’s honey; 25 % for baker’s honey from heather.

The legal limits are in Schedule 1 of the Honey (England) Regulations 2015, repeated in the Honey (Scotland) Regulations 2015, the Honey (Wales) Regulations 2015 and the Honey Regulations (Northern Ireland) 2015. The same schedule caps HMF at 40 mg/kg and sets a minimum diastase activity of 8, which is why honey must never be overheated. The fermentation thresholds come from Hanna Bäckmo’s guide to refractometers. Treat 20 % as a ceiling and aim for 18 % or less. How to measure, what to do with wet supers and how to handle heather honey are in our guide to harvesting honey.

Blending two batches

water in the blend = (weight A × water A + weight B × water B) ÷ (weight A + weight B)

A weighted average by weight, for two honeys of the same description that you want to put in one settling tank. The law allows honey to be blended only with other honey, and the limits apply to what you sell, so it is the blend that must be within the limit. A batch that has begun to ferment cannot be sold as honey at all, whatever you blend it with: smell and taste a wet batch before you use it.

Log every reading in your honey batch record.

Frequently asked questions

What is the legal moisture limit for honey in the UK?

The Honey Regulations 2015 of England, Scotland, Wales and Northern Ireland all set a maximum of 20 % water for honey in general and 23 % for heather (Calluna) honey. Baker’s honey may hold 23 %, or 25 % if it is from heather. Honey over its limit cannot be sold as honey.

What moisture content should honey be before extracting?

Aim for 18 % or less. Above about 19 % the yeasts that are always present in honey can ferment it, and the risk grows as honey sets, because crystallisation concentrates water in the liquid between the crystals. The legal 20 % is a ceiling, not a target, especially for honey that will sit in jars over winter.

How do I use a honey refractometer?

Calibrate it, let the honey and the instrument reach room temperature, then put a drop of honey on the prism without air bubbles, close the cover and read the water scale at the boundary line. Most honey refractometers read 10 to 30 % water. Sample several frames, including the uncapped cells at the edges, not just one.

How do I calibrate a honey refractometer?

Use a reference liquid of known value. Extra virgin olive oil reads about 71.5 Brix, equal to 27 % water, and can be used to set the adjustment screw if the instrument came without a calibration fluid. Recalibrate at least once a season and after it has sat unused, with the instrument at room temperature.

Can I dry honey that is too wet?

Before extraction, yes: stack the supers criss-cross in a small warm room with a dehumidifier for a day or two. Once honey is in a bucket, drying it is slow and difficult. Blending only helps if the blend ends up within the limit and the wet honey has not begun to ferment, which would rule it out as honey altogether.

Why is heather honey allowed more water?

Ling heather (Calluna vulgaris) honey is naturally wetter and thixotropic: it sets like a jelly and has to be pressed or loosened before it will spin out. The law recognises this with a 23 % limit instead of 20 %. Even so, heather honey well under 20 % keeps far better than honey near the limit.

Where can I get honey moisture tested in a lab?

Fera Science at York offers a moisture in honey test by refractive index, listed at £360 per sample excluding VAT in October 2026, with a ten working day turnaround. A lab result is worth having before selling a large batch or entering a dispute; for routine checks a calibrated refractometer does the job.

Sources

  1. The Honey (England) Regulations 2015, Schedule 1: compositional criteria, legislation.gov.uk
  2. The Honey (Scotland) Regulations 2015, legislation.gov.uk
  3. The Honey (Wales) Regulations 2015 (SI 2015/1507, W. 174), legislation.gov.uk
  4. The Honey Regulations (Northern Ireland) 2015, legislation.gov.uk
  5. Moisture in honey test, Fera Science
  6. Refractometer: all you need to know (Hanna Bäckmo, reprinted from The Irish Beekeeper), Bee Culture
  7. Honey: beekeeping education module 10 (with notes), SRUC, Scotland’s Rural College

Calculators