Why did my cheese sauce go grainy?

Cheese is protein and fat held loosely together. Above about 70°C the protein contracts and expels the fat, leaving stringy solids in a greasy liquid. Almost every grainy cheese sauce is a sauce that got too hot.

Step by step

1. Take it off the heat before adding cheese.The residual heat in the sauce is plenty to melt it. Cheese added to a simmering sauce splits within seconds.
2. Add the cheese gradually.A handful at a time, whisking until melted before the next. Dumping it all in cools the sauce unevenly and clumps.
3. Grate it finely.Fine gratings melt quickly at low temperature. Chunks need more heat to melt, which is the thing causing the problem.
4. Choose a cheese that melts well.Mature cheddar, gruyère, comté and emmental melt smoothly. Very aged hard cheeses and low-fat cheeses split much more readily.
5. Build it on a proper roux base.The starch in a roux stabilises the emulsion and makes the sauce far more tolerant of heat.
6. Rescue a split sauce with cold liquid.Off the heat, whisk in a splash of cold milk or cream. Often it comes straight back together.
7. Blend it if whisking does not work.A stick blender forces it back into an emulsion. The texture is usually indistinguishable.

Tips

• A pinch of cornflour tossed with the grated cheese before it goes in acts as a stabiliser. It is what makes packet sauces so reliable.
• Never boil a finished cheese sauce, including when reheating. Warm it gently and stir.
• Pre-grated cheese is coated in anti-caking starch, which actually helps here even though it melts less smoothly overall.

Common mistakes

• Adding cheese to a boiling sauce — The proteins tighten instantly and squeeze out the fat. This is the definition of a split sauce.
• Using a very low-fat cheese — There is less fat to hold the emulsion together, so it goes stringy and grainy much more easily.

Questions people ask