Allicin: The Chemistry Behind Garlic's Bite
Allicin is the sharp, pungent compound responsible for the bite of raw garlic. Intact garlic contains almost none; it forms within seconds when you cut, crush or chew a clove, as two separate substances inside the cells finally meet.
How garlic makes allicin
A garlic clove stores a mild, odourless compound called alliin in one part of its cells and an enzyme called alliinase in another. When the cell walls break, alliinase converts alliin into allicin almost instantly. It's a chemical defence: anything that bites the garlic gets a mouthful of harsh, irritating sulfur.
This is why garlic's flavour depends so much on how you cut it:
| Preparation | Cells broken | Flavour |
|---|---|---|
| Whole clove | Very few | Mild, sweet once cooked |
| Thin slices | Some | Gentle, nutty |
| Minced | Many | Strong |
| Pressed, grated or pasted | Most | Sharpest and hottest |
Why allicin doesn't last
Allicin is unstable. Within hours at room temperature, and much faster with heat, it breaks down into other sulfur compounds such as diallyl disulfide and ajoene. These are milder, rounder and more savoury. That's the shift you taste between a raw garlic aioli and roasted garlic.
Heat also destroys the alliinase enzyme. If you roast or boil cloves whole before cutting them, very little allicin ever forms, which is why roasted garlic is soft, sweet and spreadable instead of fiery.
Cooking tips
- Want gentle garlic? Slice it, or add whole crushed cloves to oil and remove them.
- Want punch? Grate it raw into dressings or finish a dish with fresh minced garlic.
- Add it late in a stir-fry or sauté. Minced garlic burns in about 30 seconds in hot oil and turns bitter. Add it after onions have softened, or sweat it gently.
- Acid tames it. Letting minced garlic sit in lemon juice or vinegar for 10 minutes softens the bite for dressings.
Related compounds
Onions, leeks and chives use a similar enzyme system but make different sulfur compounds. In onions, one of them is the gas that makes you cry. Garlic's green or blue tinge when pickled is another sulfur reaction, and it's harmless.
Chef Fizz says: Garlic is a tiny chemistry kit. You decide how strong it gets the moment you pick up the knife.
Questions
Should you let garlic sit for 10 minutes after chopping?
Resting gives allicin time to form before heat stops the enzyme, which some people do for health reasons. For flavour, it mainly makes garlic sharper; skip it if you want mellow garlic.
Does cooking destroy allicin?
Yes. Allicin is unstable and breaks down quickly with heat into milder, sweeter sulfur compounds. Heat also shuts down the enzyme that makes it, so whole cloves roasted before cutting never develop much bite.
Why is pressed garlic stronger than sliced garlic?
Pressing or grating ruptures far more cells, mixing more alliin with the enzyme alliinase and producing more allicin. Thin slices break fewer cells, so they taste milder.
Why does garlic breath last so long?
One breakdown product, allyl methyl sulfide, isn't digested quickly. It enters your blood and is released through your lungs and skin for many hours.