Certain honeys contain very small amounts of bitter substances ('bitters') from various nectars or honeydews, including almond, chestnut, goldenrod, hawthorn, ivy, manuka, onion, pine, privet, ragwort, sourwood, strawberry tree, tree of heaven, wild parsley and yew. They include certain glycosides, alkaloids, polyphenols and terpenoids.

Bees avoid very bitter nectars and honeydews, but collect slightly bitter ones and are particularly attracted to those containing nicotine or caffeine.

Many people enjoy slight bitterness; others dislike it; and some are genetically unable to taste it. A very few honeys are unacceptably bitter. Processors can reduce bitterness by blending in other honeys.

The following bitters can enhance a honey's flavour:

• Amygdalin – from almond trees

• Caffeine – from citrus (especially grapefruit) and coffee trees

• Capsaicin – from chili plants

• Cocaine – from coca bushes

• Codeine, heroin, morphine and opium – from opium poppies

• Convallotoxin – from lilies of the valley

• Gossypol – from cotton plants

• Hederagenin – from ivy

• Nicotine – from tobacco

• Tannins – from oak trees

• Tetrahydrocannabinols – from marijuana plants

If present in sufficient amounts, and if enough honey is consumed, very few bitters can cause symptoms or even threaten life. They include:

• Aconitine – from aconite

• Aesculin – from horse-chestnut trees

• Atropine, hyoscyamine and scopolamine – from deadly nightshade (Atropa belladonna), datura and henbane (stinking nightshade; Hyoscyamus niger). Small quantities of datura honey can cause inebriation.

• Gelsemine – from yellow jasmine.

• Granayotoxin – from bog rosemary (Andromeda polifolia), Kalmia species such as sheep laurel and mountain laurel (calico bush or spoon-wood), pieris and Rhododendron ponticum (also called Azalea ponticum). This can cause 'honey intoxication', with sweating, nausea, vomiting, diarrhoea, fainting, dizziness, breathing problems, weakness, irregular heartbeat and convulsions. These symptoms usually last less than a day and are rarely fatal. But eating as much as 14 tablespoons of mountain laurel honey, for example, could kill a 68kg/150lb person.

• Oleandrin – from oleander

• Pyrrolizidine alkaloids – see below

• Swainsonine – from spotted locoweed (Astragalus lentiginosus)

• Tutin – from tutu (Coriaria arborea)

• Unknown substances in the wharangi bush (Melicope ternate)

Pyrrolizidine alkaloids(PAs) are present in 3 per cent of plants. They number more than 660 and include lasiocarpine in comfrey; lycopsamine in borage; and jacoline and jacozine in ragwort. Most PA-containing plants belong to the asteraceae (including ragwort and groundsel), boraginaceae (including comfrey and echiums) and leguminosae (including peas, beans and rattleworts) families. Ragwort is the most common.

Various foods, including milk, grains, eggs and honey, can contain PAs. Particularly if eaten frequently and in large amounts, one in two PAs can encourage liver disease and cancer, and damage unborn babies. However, reports of poisoning are rare, and most result from herbal remedies or teas. At the time of writing, there is no international regulation of PA levels in foods unlike for herbal remedies.

Any risk from PAs in honey is unclear, but there is probably no problem because their bitterness makes nectar less attractive to bees. Also, any PA would be present in only a very small amount after dilution in the hive by nectar and honeydew from other sources. Finally, processors tend to blend bitter honey with other honeys, which dilutes any PAs that are present. Lastly, beekeepers try to site their hives to minimize any risk from PAs.

Health benefits

Honey's bitters stimulate bile flow, which aids digestion and discourages gallstones.

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