Limonene
Also written d-limonene, r-limonene, limonine
Quick answer
The citrus-peel terpene, and the most widespread aroma compound in the spice cupboard — present in eight spices in this catalogue that a reader would never describe as citrusy.
What it does
Limonene smells of orange and lemon peel, bright and slightly resinous. Its role in spices is almost never to make them taste of citrus: it is the lift at the top of a smell, the fresh edge that arrives first and disappears first. It is why freshly cracked black pepper has a bright note that pre-ground pepper lacks entirely, why dill and caraway read as fresh despite their heavier carvone base, and why fennel seed smells brighter than its anethole content alone would suggest. The mirror-image forms smell subtly different — one more orange, one more turpentine-like — and spices carry them in different proportions.
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
Limonene is the most fugitive compound most cooks deal with, and its loss is the single best explanation of what goes wrong with old spices. It evaporates readily at room temperature from ground spice, oxidises on exposure to air into flat and faintly turpentine-like products, and boils off within seconds in a hot pan. Three practical rules follow. Grind immediately before use, because this is the fraction lost fastest and it is the one that reads as freshness. Add the bright spices late or off the heat if the top note is wanted. And judge a spice by smelling it: a spice that has lost its limonene smells muted and slightly stale rather than of nothing, and that muted smell is the most reliable freshness test there is.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- Dried orange peelPrincipal component
Dominant in fresh and young peel, and the compound whose decline is most of what deliberate ageing does to chenpi — which is why aged peel reads as marmalade rather than as orange.
- Black pepperMajor component
The compound responsible for the difference between freshly cracked and pre-ground pepper — a difference of aroma, not of heat, since piperine does not go anywhere.
- CarawayMajor component
- DillMajor component
- Dill seedMajor component
- Sichuan pepperMajor component
The citrus smell of Sichuan pepper is genuine and botanically apt: the plant is a citrus relative, and the limonene is not a coincidence of description.
- Celery seedContributing component
- Curry leafContributing component
- Dried limeContributing component
- EpazoteContributing component
- Fennel seedContributing component
- JuniperContributing component
- KorarimaContributing component
- MarigoldContributing component
- Mexican oreganoContributing component
- MintContributing component
- Pink peppercornContributing component
- SanshoContributing component
- ShisoContributing component
- Star aniseContributing component
Questions this page answers
- what is limonene
- what does limonene do
- which spices contain limonene
- what is d-limonene
- what is r-limonene