Honey crystallizes because it is a supersaturated solution. This just means that there is more sugar dissolved in the water than the water can normally hold.
There are several types of sugar found in honey, mostly glucose and fructose, but also sucrose and maltose. It is the glucose part that causes crystals to form.
Some honeys have more glucose than others. The amount of glucose depends on the flowers that produced the nectar. Honey made mostly of glucose will crystallize easily, whereas honey made with mostly fructose is very slow to crystallize.
The crystals begin forming around particles called “seeds” and then continue to multiply until a lattice builds throughout the container. There are plenty of these seeds in a jar of honey. They may be particles of dust, pollen, wax, propolis, or even air bubbles.
Several things can cause the glucose to suddenly form crystals, and it doesn’t take make much to set the process in motion. Slight changes in temperature or humidity—in the presence of the seeds—is enough to get it started.
Crystallized honey may not keep as well as liquid honey. When glucose goes from the liquid form to the crystal form, it loses some of its moisture. This moisture remains in the container and causes the total moisture in the liquid part of the honey to increase.
Honey needs to be about 18.6 percent water or less for long-term storage. If the liquid portion of the honey is more than 18.6 percent water after the crystalline glucose leaves the solution, the honey may ferment.
Fermentation is caused by yeast. But the yeast cannot grow in the low-moisture environment of cured honey. The sugar depletes the water from the yeast cells and they cannot survive. Spores of yeast remain, however, and if the water content suddenly rises the yeast can grow again.
Fermentation can be prevented by pasteurization—the process of heating the honey to 145° F for 30 minutes (or 150° F for 15 minutes) and then cooling it rapidly. This kills the yeast spores, but it also destroys some of the taste and fragrance components of honey and is generally frowned upon. In addition, heated honey often crystallizes within a few weeks and yields large, coarse crystals which give honey a crunchy—rather than a creamy—texture.
One of the popular solutions to these problems is the Dyce process of controlled crystallization, which yields a product known as “creamed” honey. I will describe the process in another post.