γ-Terpinene
Also written gamma-terpinene, g-terpinene, terpinene
Quick answer
A mild, faintly citrus terpene that matters less for what it smells of than for what it turns into: p-cymene, which is why an ageing spice grows harsh rather than merely faint.
What it does
On its own γ-terpinene is unremarkable — lightly citrus, slightly woody, and rarely the note anyone identifies in a spice. It accompanies thymol and carvacrol in thyme, oregano and savory, and cuminaldehyde in cumin, where it contributes freshness at the top of the smell without shaping it.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- high
- Fat solubility
- high
- Water solubility
- low
- Heat stability
- low
Its importance is as a precursor rather than as a smell. γ-Terpinene oxidises readily to p-cymene, and that single reaction explains the most confusing thing about old spices: a stale cumin or a stale oregano does not smell like a weaker fresh one, it smells sharper and slightly solvent-like. The compound that was contributing freshness has become the compound that contributes a dry, turpentine-adjacent harshness, so the profile has changed rather than faded. That is why toasting will not rescue a genuinely old spice, and why the storage advice in this catalogue says a spice smelling harsh is further gone than one smelling faint.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- AjwainContributing component
- Black cardamomContributing component
- Black cuminContributing component
- Coriander seedContributing component
- CuminContributing component
- OreganoContributing component
- PápaloContributing component
The second largest peak, at 20.5 per cent, in the headspace of fresh leaves from a wild population on the coast of Valencia, Spain, after p-cymene. One study, of plants growing far from where the herb is cooked with.
- SavoryContributing component
- ThymeContributing component
- YuzuContributing component
- Za'atar herbContributing 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.
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
Grinding · Decreases Cuminaldehyde, γ-Terpinene, p-Cymene, β-Pinene, volatile oil, yield
Measured against the whole seed, cumin ground at room temperature gave about a quarter less volatile oil on distillation: 3.0 per cent against 4.0 in the genotype GC 4 and 2.5 against 3.3 in RZ 209, losses the authors give as 23.2 and 24.3 per cent. Seed chilled to −30 °C with liquid nitrogen before grinding gave 4.1 and 3.6 per cent, a little more than the whole seed, which the authors put down to oil being easier to distil out of a powder. Cuminaldehyde was the main constituent of every oil. In GC 4 it made up 48.2 per cent of the oil after ordinary grinding and 56.1 per cent after cold grinding; in RZ 209 the two were close, 69.7 and 71.6 per cent. The lighter terpenes did not follow it: β-pinene, γ-terpinene and p-cymene each made up a smaller share of the oil from cold-ground GC 4 than from the ordinary grind.
Conditions: Room temperature in a domestic mixer grinder; −30 °C under liquid nitrogen in a pin mill · 50 to 100 µm from the cold pin mill; not given for the ordinary grind · Two Indian genotypes, GC 4 and RZ 209; oil distilled in water for 3 h
Grinding itself costs cumin part of its volatile oil before any storage begins, and keeping the seed cold prevents that loss. What changes in the make-up of the oil is less tidy than the total: the share of cuminaldehyde rose with cold grinding, and the shares of several lighter terpenes fell.
What this does not show: The ordinary grind was made in a kitchen mixer grinder and the cold grind in a pin mill, so machine and temperature changed together. The temperature reached in ordinary grinding and the fineness it gave are not reported. Two genotypes, three replicates, and composition as shares of the oil, not amounts in the seed.
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
Decontamination · Retains Cuminaldehyde, γ-Terpinene, p-Cymene, γ-terpinen-7-al, β-pinene, microbial load, volatile oil, colour
Cumin seed passed through an induction heater at 155 °C for 60 s showed its aerobic plate count fall from 6.21 to 2.97 on the logarithmic scale, and at 155 °C for 45 s moulds and yeasts fell by about 3.2 and coliforms by 3.6. No statistically significant difference in essential oil content was found between treated and control seed, and the oil remained within the composition of the ISO standard, with γ-terpinen-7-al (38.98 per cent), cuminaldehyde (20.75 per cent), γ-terpinene (18.81 per cent), β-pinene (13.66 per cent) and p-cymene (6.2 per cent) as the main constituents. Colour did change, increasingly with temperature and time.
Conditions: 115, 135 and 155 °C · 45, 60 and 75 s · Continuous non-contact induction heater with a screw conveyor, laboratory scale
What this does not show: Read in the abstract and conclusions only. A self-built laboratory unit; the authors themselves call for work on uniformity of heating and on how the treated seed keeps.
Measured on the spice
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
p-Cymene
What it becomes. The pair is the clearest chemical account of ageing in this catalogue: one oxidises into the other, and the spice goes from fresh to harsh rather than from strong to weak.
Questions this page answers
- what is gamma-terpinene
- what does gamma-terpinene do
- which spices contain gamma-terpinene