Honey is a supersaturated sugar solution: it holds more sugar than the water in it can keep dissolved for good. Two sugars dominate, fructose and glucose. Glucose is the less soluble of the two, so sooner or later it begins to come out of solution as tiny crystals, while the fructose stays in the liquid. The honey thickens, turns paler and eventually sets.

The sugar balance decides

How quickly this happens depends mainly on the ratio of fructose to glucose. Honeys with a fructose-to-glucose ratio above 1.33 crystallise slowly; below 1.11, quickly. Oilseed rape honey, rich in glucose, sets within days into a fine white mass, and sunflower, dandelion and clover honeys also crystallise fast. Acacia (black locust) honey, high in fructose, can stay liquid for more than a year. Water matters too: the less a honey contains, the faster it crystallises.

Temperature and seed crystals

Honey crystallises fastest between 10 and 15 °C, with around 14 °C most often cited. Above 18 °C the process slows, and below 10 °C the honey becomes so viscous that crystals form only slowly. Crystals need something to grow on: pollen grains, specks of wax or tiny air bubbles. That is why finely filtered honey stays liquid longer than honey that retains its pollen and other natural particles.

Not a fault

Crystallisation says nothing about quality. Pure honey can set, and so can honey diluted with syrup, while some genuine honeys stay runny for a very long time. Crystallisation can even be controlled: to make creamed honey by the method Elton Dyce described in 1928, about one part in ten of very finely crystallised honey is stirred into liquid honey and the mixture is left to set at around 14 °C. The new crystals copy the old ones, giving a smooth, spreadable honey.

One thing does deserve attention. Once the glucose has crystallised, the liquid part is left relatively wetter. If the honey was high in water to begin with, yeasts can multiply in it and the honey starts to ferment: it smells sour, foams and forms bubbles. White patches and streaks against the glass, by contrast, are merely tiny air bubbles between honey and jar, and do not affect quality.

How to liquefy honey gently

Stand the jar in a water bath no warmer than about 40 °C, stir now and then, and leave it only as long as it takes for the crystals to dissolve. A Brazilian study found that twenty minutes in a 40 °C water bath raised the level of hydroxymethylfurfural (HMF), a marker of heating and ageing, by about 10%; seventeen minutes in a boiling water bath raised it by 45%, and one minute in a microwave by 24%. Temperature matters more than the method. Higher temperatures also damage honey's natural enzymes and its aroma. So liquefy only as much as you will use, and do not reheat the same honey again and again – in time it will crystallise once more anyway.

Sources

  1. Polatidou et al. (2025): Physicochemical and rheological characteristics of monofloral honeys – kinetics of creaming–crystallization, Foods
  2. National Honey Board: FAQ (crystallisation)
  3. IFMG repository: HMF formation when liquefying crystallised honey (water bath and microwave)
  4. Determination of water activity change due to crystallization in honeys from Argentina
  5. Scottish Beekeepers Association: Technical data sheet 25 – Seeding honey