Thymol
Also written thymol (phenol)
Quick answer
The sharp, medicinal phenol of thyme, oregano and ajwain — and, with its isomer carvacrol, the compound that decides which of those a herb tastes like.
What it does
Thymol is penetrating, medicinal and slightly sweet, with a bitterness on the tongue and a mild burn at concentration. It is the smell of a traditional antiseptic mouthwash, which is not a coincidence — thymol was used for exactly that. Where it dominates, as in thyme and ajwain, the herb reads as clean, sharp and clinical; ajwain in particular is so thymol-forward that it is often described as a concentrated thyme, which is chemically apt even though the plants are unrelated.
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
Thymol is a phenol rather than a simple terpene, and it behaves accordingly: heavier, less volatile and considerably more heat-stable than the aromatics around it. That is why thyme is one of the few soft herbs that survives long cooking and belongs in a stock, a braise and a bouquet garni, while its lighter companions do not — and why dried thyme is a genuinely useful ingredient where dried basil is not. Its poor water solubility and strong fat solubility mean thyme gives far more to an oil, a roast or a fatty stew than to a watery one. In ajwain, the same stability is why the seed is bloomed in hot fat at the start of a dish rather than added at the end: the treatment develops it rather than destroying it.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- AjwainPrincipal component
Exceptionally thymol-dominant, which is why a small quantity reads as overwhelming and why ajwain is measured by the pinch in dishes where thyme would be measured by the spoon.
- ThymePrincipal component
- Za'atar herbPrincipal component
- OreganoMajor component
- MarjoramContributing component
Recorded in marjoram, but absent from the two marjoram oils read, both led by terpinen-4-ol; marjoram oils vary with origin.
- Mexican oreganoContributing component
An unrelated plant in the verbena family that carries the same phenols, which is the entire reason it is called oregano and the entire reason the substitution partly works.
- SavoryContributing component
Higher in winter savory. In summer savory oil it is negligible: commercial oil must carry 20–57 per cent carvacrol with negligible thymol.
- Scent leafContributing component
Dominant only in the thymol type of the species; a thyme-like note elsewhere.
- TosignContributing component
Second to carvacrol, at 10.64 per cent, in the one oil of Thymus schimperi whose analysis was read; reported as the leading phenol in the oil of another lot of Ethiopian thyme.
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.
Drying · Decreases Carvacrol, Thymol, γ-Terpinene, volatile oil
Fresh Polish oregano held 33.0 g of volatiles per kilogram, with carvacrol, thymol and γ-terpinene the main components. Drying lowered the total whatever the method, but by very different amounts: to 10.2 g/kg after convective drying at 60 °C, 13.1 g/kg after convective pre-drying with a vacuum-microwave finish, and 27.9 g/kg after vacuum-microwave drying alone.
Conditions: Convective drying at 60 °C · Compared with vacuum-microwave drying and with convective pre-drying followed by a vacuum-microwave finish
What this does not show: Read in the abstract only, which does not state the basis (fresh or dry weight) of the figures or the fate of the individual compounds. One lot of oregano.
Measured on the spice
Decontamination · Depends on conditions Carvacrol, Thymol, microbial load, water activity, colour, volatile oil
Infrared heating of moistened oregano reduced inoculated Bacillus cereus spores by 5.6 log units after 10 min at 90 °C; at 100 °C for the same time the reduction was lower, 4.7 log units, which the authors link to the water activity having fallen to 0.76 during treatment. The green colour was only slightly affected. The composition of the headspace volatiles was clearly altered, but carvacrol and thymol, two of the key aroma compounds, were only slightly affected compared with the other compounds studied.
Conditions: 90 and 100 °C · Holding times of 2 and 10 min · Oregano conditioned to water activity 0.88, in a closed infrared heating unit
What this does not show: Read in the abstract only. The oregano was moistened before treatment and would have to be dried again. Which volatiles were lost is not stated in the abstract.
Measured on the spice
Decontamination · Depends on conditions Thymol, γ-Terpinene, p-Cymene, Carvacrol, monoterpene hydrocarbons, oxygenated monoterpenes, microbial load, volatile oil
Sicilian oregano, whose oil consisted mainly of thymol and γ-terpinene with p-cymene, α-terpinene and carvacrol, showed a changed oil profile after gamma irradiation: fewer monoterpene hydrocarbons and more oxygenated monoterpenes. Total bacterial and fungal counts fell below 10 cfu/g at the lower dose, 5 kGy. A sensory panel found significant differences between irradiated and untreated oregano for every descriptor except bitter, pungent, astringent and hay.
Conditions: Gamma irradiation at 5 and 10 kGy on three cultivated Sicilian oregano samples
What this does not show: Read in the abstract only, which gives no percentages and does not say in which direction the sensory descriptors moved.
Measured on the spice
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Carvacrol
Isomers with the same formula, differing in where one group sits on the ring. Thymol reads as thyme and carvacrol reads as oregano, and the ratio between them is the single best chemical predictor of which a given leaf will taste like — including within a species, where cultivar and growing conditions shift the balance.
Questions this page answers
- what is thymol
- what does thymol do
- which spices contain thymol