Hydroxymethylfurfural (HMF) is produced from the breakdown of sugar and is used as an indicator of heat treatment and ageing. The CODEX Standard recommends a maximum limit of 40 mg/kg HMF in honey.
The rate of conversion from DHA to MG in manuka honey is temperature dependent: higher temperatures accelerate the conversion. This has led to the potential for abuse, with manuka honey being heated to quickly increase the content of MG in order to make it more valuable commercially. However if honey is heated above 30 degrees Celsius, a compound called hydroxymethylfurfural (HMF) can be created in the honey. For this reason, Analytica Laboratories includes HMF as part of its 3-for-1 Manuka Honey test, so that bee keepers can demonstrate that their honey has not been temperature-abused.