Why Does Honey Crystallise in the Jar?

A jar of honey that was once clear and pourable may gradually turn cloudy, pale or grainy. This usually does not mean that the honey has “gone bad”. It means that glucose has left the liquid phase and arranged itself into solid crystals.

Honey contains large amounts of glucose and fructose dissolved in relatively little water, so it can be treated as a highly concentrated, often supersaturated sugar solution. Fructose remains dissolved more readily, while glucose is less soluble. Under suitable conditions, glucose molecules gather around tiny particles or existing crystals to form nuclei, which then grow. The crystals incorporate some water as they form, changing the composition of the remaining liquid, so the whole jar can become thick and granular.

Different honeys crystallise at very different rates. The main influences include the balance of glucose and fructose, water content, temperature and the presence of pollen or other microscopic particles that can provide nuclei. Texture also depends on how many nuclei form and how quickly they grow. A few nuclei may develop into coarse grains; many small nuclei can produce a smoother, creamed consistency.

Crystallisation is therefore a physical change and, by itself, proves neither spoilage nor purity. If a liquid texture is preferred, a sealed jar can be warmed slowly in warm water and stirred gently, without boiling it. What matters when judging quality is evidence such as odour, fermentation and storage conditions, not the mere presence of crystals.

https://honey.com/faq
https://pmc.ncbi.nlm.nih.gov/articles/PMC9440417/