Cornflour vs plain flour
One is a whole flour and one is an isolated starch, and confusing them is made worse by the fact that the American name for each is the British name for something else.
The short answer
Cornflour is pure starch, extracted from maize with the protein, fat and fibre taken out. Plain flour is a whole milled grain — mostly starch, but carrying the protein that makes gluten. So cornflour thickens more powerfully per gram and sets clearer and firmer, and it contributes no structure whatever. Substituting it for flour in a bake removes the network rather than replacing it; adding a little of it to flour is a deliberate way of weakening that network, which is the basis of the home cake-flour substitute. The naming is a trap: British cornflour is American cornstarch, and American corn flour is finely milled maize, which is a different product again.
Where they differ
| Dimension | First | Second |
|---|---|---|
| What it is | Isolated starch. No protein, fat or fibre. | A whole milled grain. |
| Structure contributed | None. It cannot form a network. | The gluten network. |
| Thickening power | Roughly twice that of flour by weight. | Lower, and it brings flavour with it. |
| Set appearance | Cloudy but translucent; firm. | Opaque and matt. |
| Naming | UK cornflour = US cornstarch. US “corn flour” is milled maize, not this. | UK plain = US all-purpose. |
Differences that do not matter
These are real distinctions that are unlikely to change your decision. They are listed so you can stop thinking about them rather than left out so the comparison looks decisive.
- Taste when undercooked. Chalky. Must be boiled out. Raw and pasty. Must be cooked out.
Three things sold as corn something, and only one of them is this
British cornflour and American cornstarch are the same product: a fine white powder of isolated maize starch, used to thicken.
American CORN FLOUR is finely milled whole maize — yellow, with the protein and oil still in it. It behaves like a flour, not like a starch.
CORNMEAL and polenta are the same grain milled coarser still, and are used for texture rather than for thickening or structure.
A recipe that says “corn flour” without saying where it was written is genuinely ambiguous, and the two readings produce completely different results. The colour is the quickest tell: the starch is white and the flour is yellow.
Related
Compares
An isolated starch against a whole grain, and the naming trap where each country's word means the other's other product.
An isolated starch against a whole grain, and the naming trap where each country's word means the other's other product.