p-Cymene
Also written para-cymene, p cymene
Quick answer
A dry, woody, faintly solvent-like terpene that sits under cumin, oregano and nigella — rarely the point of a spice, and often the reason an old one smells harsh.
What it does
p-Cymene contributes a dry, thin, woody note with a faint turpentine edge. It is seldom pleasant on its own and is rarely what a spice is valued for; its role is structural, giving cumin and nigella part of their dusty, earthy character and supporting the phenols in oregano and thyme. It is also one of the products formed when other terpenes oxidise, which is why it becomes more prominent as a spice ages and why stale cumin smells sharper and more solvent-like rather than simply weaker.
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
- moderate
The useful consequence of p-cymene is diagnostic rather than culinary. Because it accumulates as a spice oxidises while the pleasant aromatics disappear, a spice whose smell has shifted from rounded to sharp and slightly solvent-like has not merely faded — it has changed, and toasting will not bring it back. This is the chemical basis of the advice on the storage pages that 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.
- CuminMajor component
- NigellaMajor component
The largest component of an analysed nigella oil, at about 32 per cent.
- AjwainContributing component
- Black cuminContributing component
- EpazoteContributing component
- Mexican oreganoContributing component
- OreganoContributing component
- PápaloContributing component
The largest single peak in the headspace of fresh leaves from a wild population on the coast of Valencia, Spain, at 26.1 per cent of the volatiles collected, ahead of γ-terpinene. One study, of plants growing far from where the herb is cooked with, and no panel tied the compound to the smell.
- SavoryContributing component
- ThymeContributing component
- VoatsiperiferyContributing component
Rises markedly when the berries go through the wet process of blanching and sweating.
- 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.
Toasting and dry roasting · Decreases p-Cymene, Thymoquinone
Thymoquinone and p-cymene were the major volatiles of nigella seed whether raw, conventionally roasted or roasted by microwave, and the levels of both fell with roasting.
Conditions: in air · Microwave roasting at 0.45 kW for 2, 4 and 8 min; conventional roasting · Headspace SPME GC-MS; 38 volatiles identified
What this does not show: Read in the abstract only, which gives no amounts and does not state the temperature of the conventional roasting.
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
Questions this page answers
- what is p-cymene
- what does p-cymene do
- which spices contain p-cymene
- what is para-cymene
- what is p cymene