The encyclopaedia of gravy
Reduction concentrates flavour, gelatin and body by evaporating water. It is how a jus gets its gloss and how a thin gravy gets its depth.
Reduction is the simplest technique in cooking: boil a liquid so that water leaves as steam and everything else stays behind, more concentrated than before.
For gravy it does three things — deepens flavour, increases body through concentrated gelatin, and darkens colour.
How much to reduce¶
| Target | Reduce to | Result |
|---|---|---|
| Gravy base | ¾ of the volume | Rounder, deeper flavour |
| Strong gravy | ½ | Noticeably richer; check salt |
| Jus | ⅓ | Glossy, coats a spoon without starch |
| Glace | ⅒ | Syrupy, sets solid when cold; a seasoning, not a sauce |
Method¶
- Use a wide pan. Evaporation happens at the surface, so a wide sauté pan reduces two to three times faster than a tall saucepan with the same volume.
- Bring to a strong simmer, not a rolling boil. A violent boil emulsifies fat into the liquid and makes it cloudy and greasy.
- Leave the lid off entirely. A lid means condensation falls back in and nothing reduces.
- Skim any scum or fat that gathers at the edges.
- Judge by eye: mark the level with a wooden spoon at the start if you want to be precise.
⚠️ Season afterwards
Salt does not evaporate. A stock seasoned before reduction becomes inedible after it. This is the single most common way to ruin a reduction, and it cannot be undone — see fixing gravy that is too salty.
Why reduced stock feels different in the mouth¶
Good stock contains gelatin, dissolved out of collagen in bones and connective tissue. As water leaves, the gelatin concentration rises, and gelatin gives liquid a distinctive coating, lip-sticking quality at concentrations far too low to actually set.
This is why a reduced homemade stock can be glossy and full-bodied with no flour at all, and why a reduced stock cube simply becomes salty water. There is no gelatin in a cube. See gelatin from bones.
Reduction and alcohol¶
When you deglaze with wine, beer or cider, reduce it before adding stock. Alcohol cooked briefly tastes raw and sharp; reduced by half it tastes sweet and rounded. Two to three minutes of hard bubbling is usually enough for 150 ml.
When not to reduce¶
- When the stock is already salty — reduce a low-salt stock instead, or dilute first.
- When you have added cream or butter — both split under prolonged hard heat.
- When you have thickened with cornflour — extended boiling breaks it down and the gravy thins.