Cornflour
Pure maize starch — the reference thickener, and in baking a diluent that removes protein from a flour rather than adding anything to it.
Also called cornstarch (US); corn starch (US); corn flour (US) — AMBIGUOUS AND WORTH CARE. In American usage 'corn flour' often means finely milled whole maize — a yellow flour used for cornbread — while the white starch is 'cornstarch'. British 'cornflour' always means the starch.; maize starch (INTERNATIONAL); flour vs cornstarch (US)
Cornflour is maize starch with the protein, fat and fibre removed. That absence is what it is for.
As a thickener it gelatinises into a clear, glossy gel and sets soft. As a baking ingredient it is used to DILUTE — replacing part of the wheat flour in a formula lowers the protein of the mixture without changing the bulk, which is how cake flour is imitated at home and why cornflour appears in shortbread and in delicate biscuits. What it adds is nothing; what it does is take gluten potential away.
It is not a substitute for flour in any structural sense. A cake made entirely of cornflour has no gluten, no protein network and nothing but gelatinised starch holding it, so it is fragile and pasty. The relationship runs one way: cornflour can replace some flour to weaken a mixture, and flour cannot replace cornflour where a clear soft-setting gel was wanted.
What changes if it is left out
Where it was thickening, another pure starch does the same job with a different set texture. Where it was diluting a flour, leaving it out raises the protein of the mixture and gives a chewier, tougher result — which is exactly the effect it was added to prevent.
Follows from the two functions recorded on this ingredient and from the gelatinisation science, which carries passage-verified support.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Related
What it does
Structure building
Gelatinised starch sets a soft structure. It is the whole of what cornflour contributes and it is why a cornflour-only bake is fragile and pasty.
Gluten inhibition
THE FUNCTION IT IS USUALLY ADDED FOR. Replacing part of the wheat flour lowers the protein of the mixture without changing the bulk — it takes gluten potential away rather than adding anything.
Compared in
Cornflour vs tapioca vs potato starch vs arrowroot
A subject of the comparison, so it is reachable from the record a reader is more likely to land on first.