The encyclopaedia of gravy
An emulsion suspends fat as tiny droplets through the liquid. Starch, gelatin, mustard and vigorous whisking all help; boiling and standing break it apart.
Why fat floats¶
Fat and water do not mix. Left alone, fat droplets coalesce and rise, giving the greasy film on a badly made gravy.
An emulsion is fat broken into droplets small enough, and stabilised well enough, to stay suspended. Emulsified fat is not visible as fat: it reads as richness, body and gloss.
What keeps gravy emulsified¶
Starch. Swollen starch granules physically get in the way of droplets meeting each other, and the viscous liquid slows their rise. This is a large and under-appreciated part of what flour does in a gravy — it is why a floury gravy tolerates fat that would separate out of a thin jus.
Gelatin. Long protein chains act as stabilisers at the fat–water boundary. Another reason good stock makes better gravy. See gelatin from bones.
Mustard. Contains natural emulsifiers. A teaspoon genuinely helps. See mustard in gravy.
Agitation. Whisking breaks fat into smaller droplets; smaller droplets rise more slowly.
Mounting with butter¶
The classical finish, monter au beurre: whisk cold butter, in small cubes, into a hot but not boiling sauce, off the heat.
Cold butter is crucial. As it melts slowly under agitation, its fat disperses into droplets and the milk solids and phospholipids in the butter act as emulsifiers. Butter melted first and poured in simply floats.
The result is gloss and a rounded mouthfeel. Do not boil the sauce afterwards, or it will separate. See jus.
Why it breaks¶
| Cause | What happens |
|---|---|
| Boiling | Droplets gain energy, collide and coalesce |
| Standing | Droplets slowly rise and merge |
| Too much fat | Not enough liquid or stabiliser to hold it |
| Adding cream then boiling | Dairy proteins coagulate; the emulsion collapses |
| Too much acid with dairy | Same effect |
Fixing a split gravy¶
- Off the heat, whisk hard.
- Add a splash of cold stock, or a tablespoon of cold water, while whisking — the temperature drop plus agitation often brings it back.
- A stick blender will usually rescue it.
- As a last resort, strain off the free fat and re-thicken.
Flour-thickened gravies are far more forgiving than reductions, because the starch is doing most of the stabilising work.