Eugenol
Also written eugenol (clove oil), 4-allyl-2-methoxyphenol
Quick answer
The smell of cloves, and the compound that carries a genuine local anaesthetic effect — the reason a clove held against a sore tooth is a practice found in a dozen unconnected traditions.
What it does
Eugenol is the sweet, medicinal, faintly bitter smell of cloves, and it is unusually dominant: clove oil is largely eugenol, which is why cloves are among the hardest spices to use subtly and why a single clove too many is instantly recognisable. It produces a distinct numbing sensation on the tongue and gums at concentration, separate from its aroma. In allspice it sits alongside enough other aromatics to read as one note in a compound smell rather than as the whole of it, which is precisely why allspice is often described as a blend of cloves, cinnamon and nutmeg and is in fact a single berry.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- moderate
- Fat solubility
- high
- Water solubility
- low
- Heat stability
- high
Eugenol is more heat-stable than most aroma compounds and it is stubbornly fat-soluble, and both facts show up in how cloves are used everywhere they are used. It survives long braising, roasting and baking with its character intact, which is why cloves are a fixture in dishes cooked for hours — hams, stocks, biryani, mulled wine — and why the traditional applications almost all involve extended cooking rather than a finishing touch. Its poor water solubility means that a clove simmered in a watery liquid gives up its aroma slowly and incompletely; in a fatty stock or in wine it extracts readily. The practical consequence cooks discover the hard way is that eugenol accumulates rather than dissipates: a long-cooked dish gets more clove-forward with time, not less, so cloves are counted into a braise at the start and removed, not added freely.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- AllspicePrincipal component
The reason allspice reads as clove-adjacent. It is a genuine chemical relationship rather than a coincidence of description.
- Bois d'IndePrincipal component
The leading component of the leaf oil in most chemotypes of the West Indian bay tree, and the reason its leaf does the work in a Caribbean broth that allspice berries do elsewhere — the two are one genus.
- ClovesPrincipal component
- Scent leafPrincipal component
Dominant in the eugenol type of Ocimum gratissimum that West African cooks mostly grow, and the reason scent leaf smells of cloves rather than of basil.
- Cinnamon (Ceylon)Major component
Present in true cinnamon and essentially absent from cassia. This is the single biggest chemical difference between the two barks and the one a taster notices.
- Tej pattaMajor component
About 18 per cent of a leaf oil distilled from Bangladeshi market leaves, behind linalool; the authors note that published leaf oils of this species differ widely with origin.
- BasilContributing component
Varies enormously by cultivar. Holy basil and several Asian basils are markedly eugenol-forward, which is why they read as clove-like and why they are not interchangeable with sweet basil.
- Bay leafContributing component
- Hoja santaContributing component
What cooking and processing were measured to do to it
Findings from studies in which this compound was followed through heat, fat, water, drying or storage. Each belongs to its study and its conditions.
Grinding · Increases Eugenol, Cyperene, Phenethyl isovalerate, volatile oil, yield
Clove buds ground before being boiled in water gave up twice as much essential oil as whole buds: 14.3 per cent of their weight against 7.14 per cent after six hours of distillation. The composition changed as well. Eugenol was the major compound in both oils, but it made up 87.4 per cent of the oil from whole buds and 68.7 per cent of the oil from ground ones, in which cyperene rose from 7.2 to 20.5 per cent.
Conditions: in water · Boiling water at atmospheric pressure · 6 h of hydrodistillation · 50 g of clove buds, whole or ground in an electric grinder, in 500 mL of water
A whole clove releases its oil slowly and incompletely even to hours of boiling, which fits its use whole in long-cooked dishes; ground clove gives up much more, and a broader mixture of compounds.
What this does not show: One lot of cloves and one grinder, with composition as relative peak areas. Distillation removes the oil continuously, so the yields are not the amounts that would be found in a cooking liquid.
Measured on the spice
Drying · Decreases Eugenol, Linalool, methyleugenol, eucalyptol (1,8-cineole), volatile oil, drying time
Fresh sweet basil held 32.1 g of volatiles per kilogram, with methyleugenol, eugenol, eucalyptol and linalool the main components. Both convective and vacuum-microwave drying brought the total down to 14.4 g/kg, less than half. Convective pre-drying at 40 °C followed by a vacuum-microwave finish at 360 W kept 16.7 g/kg and gave dried basil in which a panel still found strong fresh and floral notes.
Conditions: Combined method at 40 °C and 360 W · About 250 min for the combined method
What this does not show: Read in the abstract only. The best method still lost about half of the volatiles, and the abstract does not say which compounds were lost most.
Measured on the spice
Drying · Depends on conditions Linalool, Eugenol, volatile oil
Of three ways of drying basil, air drying at room temperature brought about only small losses of volatile components, while oven drying at 45 °C and freeze-drying both decreased the total considerably. Linalool was the major component, followed by eugenol. The odour changed in kind as well as strength: fresh basil was described as fresh, herbaceous and floral, the dried samples as mentholated, spicy, hay-like and earthy.
Conditions: in air · Oven at 45 °C; air at room temperature; freeze-drying
What this does not show: Read in the abstract only, which gives no amounts. Its finding that freeze-drying lost much of the volatiles runs against the common assumption that freeze-drying preserves aroma best, and other studies of other basils may differ.
Measured on the spice
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Safrole
Structurally close relatives, and their regulatory treatment could not be more different: eugenol has an established acceptable intake as a flavouring, and safrole is prohibited outright as a food ingredient in the United States.
Regulatory position
Held on the compound, because the restriction is a fact about the molecule rather than about any one spice.
International (Codex/JECFA)
permittedJECFA evaluation of eugenol and related hydroxyallylbenzene derivatives
Eugenol has been evaluated as a flavouring substance and carries an acceptable daily intake. This is a statement about eugenol added as an isolated flavouring, not a limit on cloves, and the figure itself must be read from the monograph rather than quoted second-hand.
Safety
What the concern is. The dose, the population and the evidence level live on the spice profiles, which is where a reader with that question actually arrives.
The exposure that carries documented concern is clove oil rather than cloves: the concentrated oil has been associated with liver injury in overdose, particularly in children, and it is an oral mucosal irritant. Whole and ground cloves used as a seasoning are not the same exposure and no competent source in this library treats them as one.
Questions this page answers
- what is eugenol
- what does eugenol do
- which spices contain eugenol
- what is 4-allyl-2-methoxyphenol