1. Understanding honey crystallisation

Honey crystallisation is a natural phenomenon governed by chemical and physical processes. Liquid honey is generally a glucose-supersaturated solution: it contains more dissolved glucose than could remain permanently in solution under equilibrium conditions. Its behaviour depends in particular on sugar composition, water content, temperature, viscosity and the presence of crystal seeds.

In a sugar solution, there is a solubility limit beyond which the sugars can no longer remain fully dissolved. Between the saturated state and spontaneous crystallisation lies a region known as the metastable zone. Honey may remain liquid in this zone for some time, but a change in temperature, stirring or the presence of pre-existing crystals can trigger crystallisation.

Most liquid honeys therefore remain in a metastable state for a variable period. The fact that a honey remains liquid for a long time does not mean that it is not supersaturated. The crystallisation rate results from the interaction of sugar composition, water content, temperature, viscosity and the number of crystal seeds present.

2. Nucleation and crystal growth

Crystallisation is the gradual transition of part of the dissolved sugars from the liquid to the solid state. Three overlapping phases can be distinguished: diffusion or pre-crystallisation, during which sugar molecules move and encounter one another; nucleation, during which small stable crystals form; and crystal growth, during which these crystals incorporate further dissolved sugar molecules.

Viscosity influences molecular mobility and therefore the rate of diffusion. The final texture also depends on the number and distribution of crystal seeds. A large number of well-distributed seeds generally favours the formation of many small crystals. When only a few seeds are present, the crystals that have already formed may grow larger and produce a coarser texture.

The crystallised mass generally retains a liquid phase between the crystals. The proportion and distribution of these two phases vary according to the type of honey and the storage conditions. The denser the crystal network, the firmer the final consistency.

3. Role of water content and the glucose/water ratio

Honey can be described as a system composed predominantly of sugars and water. Water content influences the dilution of the sugars and therefore the rate of crystallisation. The glucose/water ratio is a useful empirical indicator: the lower it is, the more the honey generally tends to remain liquid; the higher it is, the more likely and rapid crystallisation becomes.

Higher water content generally reduces glucose supersaturation and may slow crystallisation. At the same time, it increases the risk of fermentation. Above approximately 18 %, this risk is often considered more significant, but this value is not a universal biological threshold. The composition of the honey, its water activity, the yeasts present, temperature and storage duration must also be taken into account.

Very dry honey, by contrast, becomes particularly viscous. The resulting reduction in molecular mobility can slow both diffusion and crystal growth. No single water-content value can therefore predict the final texture with certainty.

In the data presented in the source article, 79 % of honeys with a glucose/water ratio below 1.60 were fluid, whereas 97 % of honeys with a ratio above 2.20 were firm to spreadable. These results are empirical observations from a specific data set and are not universally valid thresholds. Between these two ranges, the final texture is considerably more difficult to predict (Dailly, 2008).

Water content must also be distinguished from water activity. During crystallisation, the remaining liquid phase may become relatively richer in water and fructose, causing its water activity to increase in some cases. This does not automatically lead to fermentation, but in an already relatively moist honey it may reduce the stability margin (Tabouret, 1979; Gleiter et al., 2006).

4. Influence of sugar composition

The two principal sugars in honey are fructose and glucose. Fructose is considerably more soluble than glucose: honey rich in fructose therefore tends to crystallise slowly, whereas honey rich in glucose generally crystallises more rapidly.

The fructose/glucose ratio, often abbreviated as F/G, provides an empirical indication of the tendency to crystallise. In the data presented in the source article, 89 % of honeys with a ratio below 1.05 were firm or spreadable, whereas 90 % of honeys with a ratio above 1.45 were fluid. These values are statistical reference points rather than natural boundaries that can be applied to all honeys.

Other sugars, particularly di- and trisaccharides, also influence viscosity, hygroscopicity and molecular mobility. They may therefore modify or partly counteract the apparent effect of the fructose/glucose ratio. Some honeydew honeys may consequently remain liquid despite a relatively low F/G ratio.

Melezitose and other oligosaccharides are particularly relevant in honeydew honeys. A high melezitose content can promote rapid crystallisation in the comb and make the honey difficult or even impossible to extract using conventional methods. When this behaviour becomes apparent, early action is required.

5. How to promote fine crystallisation

Analytical indicators are useful, but they are not always sufficient to predict honey behaviour precisely. A large proportion of honeys falls into intermediate ranges where the final texture depends strongly on temperature, the crystal seeds present and the practical handling applied by the beekeeper.

Storage temperature is a major influence. As temperature falls, glucose solubility decreases and crystallisation becomes more likely. At very low temperatures, however, viscosity increases sharply and molecular mobility slows. For many honeys, a temperature of approximately 10 to 15 °C favours rapid crystallisation; several observations point to an optimum around 14 °C. A temperature of 20 to 25 °C generally allows liquid honey to remain liquid for longer. These values are indicative, since sugar composition and water content affect crystallisation kinetics.

Seeding consists of adding already finely crystallised honey to liquid honey in order to introduce numerous crystal seeds. A rapidly crystallising honey, such as some oilseed-rape honeys, may be suitable if it has a fine and uniform structure. In the experiments described in the source article, seeding rates of 8 to 10 % produced fine crystallisation. These results relate to a specific procedure and do not constitute a universal recipe. The optimal amount depends on the honey, the fineness of the starter honey, the temperature and the desired texture (Dyce, 1931; Dailly, 2008).

When only a limited amount of starter honey is available, a small quantity of honey can first be seeded and then incorporated into the ripener once crystallisation has begun. This is part of practical experience and must be adapted to the conditions of the individual operation.

The fineness of the starter crystals is also important. The finer and more evenly distributed the crystal seeds, the finer the final grain tends to be. The result nevertheless also depends on the composition and temperature of the honey.

6. Effects of mixing, stirring and potting

Controlled stirring can distribute crystal seeds throughout the mass. Combined with seeding, it may promote finer and more uniform crystallisation. Historical experiments demonstrate this effect for particular procedures and honey types, but they do not establish a generally valid stirring duration or frequency (White et al., 1962).

When crystallisation is already well advanced, regular stirring may prevent the formation of an excessively dense crystal network and produce a creamy rather than very firm texture. The result depends on the timing, temperature, viscosity and intensity of stirring.

The use of a pump can have a similar effect to stirring. However, improper use or excessive movement may incorporate air into the honey. These bubbles can alter the appearance of the product and must not be confused with fermentation.

Some industrial processes deliberately introduce microbubbles into honey to produce a creamy texture. This is a specific process and should not be equated with spontaneous crystallisation or simple seeding. Microbubbles are therefore not an indicator of quality, authenticity or fermentation.

Potting can also influence the rate and appearance of crystallisation. Dividing honey into smaller containers changes heat exchange, contact area and diffusion distances. The effect depends on the type of container, temperature and crystal seeds present and should not be reduced to a simple “catalytic” effect.

7. Common problems related to crystallisation

Marbling, whitish areas or visible differences at the surface or along the walls of jars are generally related to crystallisation and the reorganisation of phases. Temperature fluctuations can make these structures more visible. They are not evidence of incorporated air and are not necessarily a sign of quality deterioration.

When crystallised honey cools, differences in expansion and contraction between the honey, its liquid phase and the container may slightly alter the appearance of the surface. In firm honey, the crystalline structure of the glucose may become visible as whitish streaks. A stable storage location from the time of potting helps to limit these visual changes.

Two-phase separation may occur when water content, sugar profile, temperature and nucleation conditions interact unfavourably. In historical observations, a fructose/glucose ratio below approximately 1.45 was associated with this phenomenon. This value is not a universal threshold.

The upper layer is often more liquid and relatively richer in fructose and water, while the lower layer is more strongly crystallised and richer in glucose. Crystallisation may therefore increase water activity in the remaining liquid phase and, in honey that was already relatively moist, increase the local risk of fermentation. Phase separation is nevertheless not the same as fermentation.

Managing temperature and crystallisation techniques according to the water content and sugar profile of the harvested honey can help to guide the final texture. Processing should be as brief and moderate as possible in order to limit air incorporation and the impairment of aromas and enzymes.

Conclusion: crystallisation is a natural property of honey and is not in itself a quality defect. Its rate and texture depend mainly on sugar composition, water content, temperature, viscosity and the crystal seeds present. Appropriate seeding, stirring, storage and potting practices can guide the process. The numerical values should nevertheless always be interpreted as indicative and in relation to the type of honey and the procedure used.

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See also:

• Managing honey water content
• Optimising good beekeeping practices for honey production
• The beekeeping value of forage plants
• Forage plants
• All about honey

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References cited in the text

Dyce, E. J. (1931). Fermentation and crystallisation of honey. Bulletin of the Cornell Agricultural Experiment Station, 528.

White, J. W., Jr., Reithof, M. L., Subers, M. H., & Kushnir, I. (1962). Composition of American honeys. Technical Bulletin, U.S. Department of Agriculture, 1261.

Tabouret, T. (1979). Rôle de l’activité de l’eau dans la cristallisation du miel. Apidologie, 10(4), 341–358. https://doi.org/10.1051/apido:19790403

Gleiter, R. A., Horn, H., & Isengard, H.-D. (2006). Influence of type and state of crystallisation on the water activity of honey. Food Chemistry, 96(3), 441–445. https://doi.org/10.1016/j.foodchem.2005.03.051

Dailly, H. (2008). Crystallisation of honey: Knowledge and practice. Abeilles & Cie, 124.