Allicin
Also written diallyl thiosulfinate
Quick answer
The compound responsible for the smell of cut raw garlic — which does not exist in the intact clove, forms within seconds of cutting, and has largely decomposed again within minutes.
What it does
Allicin is the sharp, hot, sulfurous character of raw garlic, with a genuine chemical sting on the tongue at high concentration. It is not the smell of cooked garlic, which is sweet, nutty and mellow, and it is not the smell of an unbroken clove, which is very faint. Its own breakdown products are what most garlic actually tastes of: allicin is unstable and converts within minutes into a family of sulfides that are more persistent, less aggressive, and responsible for both cooked garlic flavour and garlic breath.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- moderate
- Fat solubility
- moderate
- Water solubility
- moderate
- Heat stability
- low
Everything cooks understand about garlic timing follows from the fact that allicin is made on damage and then immediately begins to fall apart. How finely garlic is cut determines how much forms — a whole clove barely any, a crushed one a great deal — which is why crushed garlic is far more assertive than sliced at identical weight, and why recipes specify the cut rather than the quantity alone. Resting cut garlic for a minute before it meets heat allows the reaction to complete; adding it straight to hot fat inactivates the enzyme first and gives a milder result, which is sometimes the intention. Heat destroys allicin rapidly, so cooked garlic is a different flavour rather than a weaker one, and garlic added at the start of a braise and garlic added at the end are not the same ingredient. Acid also slows the enzyme, which is why raw garlic pounded into a dressing is gentler than the same garlic pounded alone.
Not present until the plant is damaged
Alliin + Alliinase
The intact clove stores alliin separately from the enzyme alliinase. Cutting or crushing brings them together and allicin forms within seconds. Because allicin is itself unstable, its concentration peaks shortly after cutting and then declines, so garlic prepared and left is chemically not the garlic that was cut.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- GarlicPrincipal component
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Syn-propanethial-S-oxide
The onion equivalent, and the reason onions make people cry. Onions run the same kind of enzymatic defence on a different stored precursor and produce a different, volatile, eye-irritating product — so the mechanism is shared and allicin itself is not, which is why the onion profile does not record it.
Allyl isothiocyanate
Both are pungent sulfur compounds released by enzyme action on damage, and neither exists in the intact plant. They come from unrelated plant families and unrelated precursors.
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.
Garlic is a documented hazard to dogs and cats, in which Allium species cause damage to red blood cells; the concern is veterinary and is recorded in full on the garlic profile against a veterinary source. In people the relevant considerations are contact dermatitis from prolonged handling of raw garlic and the interaction concerns attached to concentrated garlic supplements rather than to food.
Questions this page answers
- what is allicin
- what does allicin do
- what is diallyl thiosulfinate