Hydroxymethylfurfural (HMF) is a break-down product of fructose (one of the main sugars in honey), it forms slowly during storage and very quickly when honey is heated. According to Hills Laboratories HMF is created by the thermal decomposition of sugars and can provide evidence that honey has been heated or 'cooked'.
Fresh natural honey can have varying levels of HMF. In the hive honey would normally be below 1 mg/kg but levels soon start to rise with ambient temperatures above 20°C. It should be noted that temperatures in the beehive can rise to over 40°C during summer months (when the main honey crop is in progress). It is usual for HMF to be below 10 mg/kg in fresh extracted honey. Levels higher than this may indicate excessive heating during the extraction process. The international food standards requires that the hydroxymethylfurfural content of honey after processing and/or blending shall not be more than 40 mg/kg.
Sweetree honey is tested for HMF levels and are well below 10mg/kg, indicating very low levels of heating and very fresh honey!