Why honey crystallises

Honey is holding more sugar than it can dissolve

Honey is a supersaturated solution: it contains far more sugar than that quantity of water could normally hold. It is metastable, meaning it will stay liquid until something gives the sugar a reason to come out of solution — and then, once started, the process continues.

The sugar that comes out is glucose. Fructose is roughly twice as soluble and stays in solution; glucose reaches saturation first and crystallises as glucose monohydrate. This is why the glucose-to-fructose ratio predicts crystallisation better than anything else, including colour.

What else changes the rate

• Nucleation sites. Crystals need something to start on: pollen grains, dust, air bubbles, or existing crystals. This is exactly why ultrafiltered honey stays liquid far longer — the starting points have been removed — and why a jar that has begun to set will finish quickly.
• Temperature. Crystallisation is fastest at around 14 °C. Warmer and the sugar stays dissolved; much colder and the honey becomes too viscous for molecules to move into position. A kitchen cupboard is often close to the worst possible temperature.
• Water content. A higher moisture honey has more solvent and crystallises more slowly, though it is also more liable to ferment.
• Agitation. Stirring distributes seed crystals and speeds things up. This is not a defect to avoid but a tool — it is how creamed honey is made deliberately.

What to do about it

Two honest options. The first is to eat it as it is — set honey spreads better than liquid honey and does not run off toast, which is the entire commercial argument for creamed honey.

The second is to redissolve it. Stand the jar in water at around 40-50 °C and leave it, stirring occasionally, until the crystals go. It will take a while and that is fine. What matters is not rushing: high heat destroys aroma compounds, degrades enzymes and drives up hydroxymethylfurfural, and a microwave does all three unevenly and fast. Redissolved honey will also crystallise again, usually sooner, because some crystal nuclei survive.