Honey to be consumed within three to four months of purchase should be stored in a sealed glass rather than a plastic jar, out of sunlight at room temperature (but below 22°C).
While being stored honey can start to crystallise as glucose separates and starts to form crystals which act as a catalyst for crystallisation to spread through the jar with the crystals forming a framework that retains the other components in the honey in a suspension, so turning the honey from liquid to a semi-solid state.
Honey contains both glucose and fructose sugars and small amounts of sucrose and maltose in different proportions depending on the honey. Honeys with a high percentage of glucose and low fructose crystallise fastest. Oilseed rape honeys have a high proportion of glucose so crystallise the fastest.
Filtering honey removes some of the particles that can initiate crystallisation while holding honey at temperatures over 40°C prior to bottling reduces the risk of crystallisation so processed honey is less likely to crystallise. Hence, to a degree, crystallisation is a sign of quality.
The moisture content of honey is naturally so low that it prevents yeast and other enzymes growing so is preserved. When honey starts to crystallize it can drive up the moisture content in the rest of still liquid honey to a sufficient level to allow fermentation to start. Hence to re-liquefy honey you should gently warm glass jars of crystallised honey (with the lid off) using indirect and constant heat, either in a pan of water over very low heat or ideally sous vide cooker to dissolve the sugar crystals. Ensure the water level is above that of the honey but below the top of the jar.
This de-crystallising process can take an hour or more but has no detrimental effect on the taste, so long as you keep the temperature between 35°C/95°F and 40°C/104°F (I aim for 38°C/100°F). However, repeated heating to de-crystallise will impair the flavour and aroma so only de-crystallise each jar as you need to use it.
It is possible to gently microwave honey to de-crystallise, but you will destroy beneficial enzymes in the honey.
"Creamed" honey is honey that has crystallised in a controlled way to produce fine crystals and indeed many prefer their honey crystallised, particularly to spread on toast. If you want to keep honey in a crystallised state then be sure to store it in a refrigerator.
below 0°C (32°F) - Freezing prevents crystallisation so for prolonged storage periods (over four months) honey should be frozen or at least stored in a refrigerator and for practicality, it is best to first sub-divide larger containers into smaller ones. Allow frozen honey to thaw at room temperature before use and do not refreeze.
0°C - 10°C (32°F - 50°F) - Cold temperatures help prevent crystallisation and yeast growing.
10 - 21°C (50 - 70°F) - Moderate temperatures encourage crystallisation with 14°C being the perfect honey crystallisation temperature should this be something you want to achieve.
36°C (97°F) - Hive temperature. Ideally, this is the maximum temperature honey should be exposed to.
21 - 40°C (70 - 104°F) - Warm temperatures discourage crystallisation but encourage fermentation.
40 - 71°C (104 - 140°F) - Hot temperatures destroy propolis, antioxidants and enzymes in raw honey. (This is the case in non-raw processed honey.)
Over 71°C (160°F) – Hotter temperatures pasteurise honey and also caramelise it. Pasteurisation means the honey can no longer be termed "raw honey" and many would argue that it's no longer really "honey" at all.