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Mānuka honey is a monofloral honey produced in New Zealand and Australia from the nectar of the mānuka tree. It has demonstrated antibacterial properties in vitro, but there is no conclusive evidence of benefit in medical use. It is classified under therapeutic goods in Australia, and received approval in wound management from the US Food and Drug Administration in 2007.
Mānuka honey is produced by introduced European honey bees (Apis mellifera) feeding on the mānuka or tea tree (Leptospermum scoparium and/or Leptospermum polygalifolium), which grows uncultivated throughout New Zealand and southeastern Australia.
Mānuka honey is markedly thixotropic and has shown the highest viscosity among a range of studied honeys. This property is due to the presence of a protein or colloid and is its main visually defining character, along with its typical dark cream to dark brown colour. To be labelled mānuka honey, at least 70% of its pollen content should come from Leptospermum scoparium.
The mānuka tree flowers more or less at the same time as Kunzea ericoides, another Myrtaceae species also called Kānuka, which often shares the same growing areas as the former species. Some apiarists cannot readily differentiate these two species from each other. Both flowers have a similar morphology and pollen differentiation between the two species is very difficult. Therefore, melissopalynology as identification for the type of honey is valid only in association with other identification tests. In particular, L. scoparium honey is dark, whereas K. ericoides honey is pale yellow and clear, with a "delicate, sweet, slightly aromatic" aroma and a "sweet, slightly aromatic" flavour, and is not thixotropic.
Heather (Calluna vulgaris) honey is also thixotropic, but the plant flowers in late summer and its montane distribution area does not correspond with that of Leptospermum scoparium. Therefore, its harvest cannot be mistaken for that of manuka honey.
Manuka honey has a strong flavour, which has been characterized as, "earthy, oily, herbaceous", and "florid, rich and complex". Other qualificatives used by the New Zealand honey industry are, a "damp earth, heather, aromatic" aroma and a "mineral, slightly bitter" flavour.
A 2002 review found that although the antibacterial activity of honeys (including mānuka honey) had been demonstrated in vitro, the number of clinical case studies was small. The review concluded that there was a potential for its use in "the management of a large number of wound types". A 2008 Cochrane Review found that honey may help improve superficial burns compared to standard dressing, but there was insufficient evidence from studies, many of which were on mānuka honey, to be conclusive, and the use of honey for leg ulcers provided no benefit. The review found that there was insufficient evidence for any benefit in other types of chronic wounds, as all of the data came from a single centre of research, and that "data from trials of higher quality found honey had no significant effect on healing rates or had significantly slower rates of healing". Methylglyoxal is the major antibacterial component of mānuka honey. Other smaller antibacterial effects are expected to arise from the osmolarity and pH of the mānuka honey. In vitro studies indicate methylglyoxal is an effective antimicrobial agent against forms of MRSA, although studies have not been done in humans.
In the wake of the high premium paid for mānuka honey, the majority of product now labelled as such worldwide is counterfeit or adulterated. According to research by UMFHA, the main trade association of New Zealand mānuka honey producers, whereas 1,700 tons of mānuka honey are made there annually representing almost all the world's production, some 10,000 tons of produce is being sold internationally as mānuka honey, including 1,800 tons in the UK.
In governmental agency tests in the UK between 2011 and 2013, a majority of mānuka-labelled honeys sampled lacked the non-peroxide anti-microbial activity exclusive to mānuka honey. Likewise, of 73 samples tested by UMFHA in Britain, China and Singapore in 2012-13, 43 tested negative on the same count. Separate UMFHA tests in Hong Kong found that 14 out of 55 mānuka honeys sampled had been adulterated with syrup. In 2013 the UK Food Standards Agency asked all trading standards authorities to alert all mānuka honey vendors to the need for legal compliance.
There is a confusing range of systems for rating the strength of mānuka honeys. In one UK chain in 2013, two products were labelled “12+ active” and “30+ total activity” respectively for “naturally occurring peroxide activity” and another “active 12+” in strength for “total phenol activity”, yet none of the three was labelled for the strength of the non-peroxide antimicrobial activity specific to mānuka honey.
One reason for bona fide mānuka honeys to vary in the last regard is that the bees cannot be forced to forage only on mānuka flowers, especially given the pressures toward maximal exploitation of known blooms. So intense is the demand for the correct trees that New Zealand honey farmers have been using helicopters to locate them and deploy hives nearby. There have been increasing turf disputes between producers operating close to large mānuka tree clumps, and also cases reported of many hives being variously sabotaged or stolen.
At least one British supermarket has taken to stocking jars of the honey in tagged security cassettes, such were the losses from shoplifting.