Choosing Flour: Protein Is the Whole Story

The difference is one number

What is on the bag is not a use but a protein percentage.

• Bread flour: 12-14%, from a different wheat (hard wheat).
• Plain / all-purpose: 10-11%.
• Cake flour: 7-9%, from soft wheat.

The proteins — glutenin and gliadin — meet water and, once worked, form a gluten network (dough and gluten). More protein gives a tighter, chewier net; less gives a looser, tenderer one. That is the whole mechanism; there is nothing else going on.

Which goes where

• Bread flour for anything that must rise and be chewy: bread, pretzels, pizza dough. Croissants blend bread and plain, because the dough has to hold layers without turning tough.
• Plain flour for most noodles, dumpling wrappers and pancakes. The chew of kalguksu and the stretch of a mandu wrapper live in this range.
• Cake flour for things that should crumble: cakes, cookies, and batter. Half of why tempura is crisp is low-protein flour, and the other half is ice-cold water — both are conditions that stop gluten forming (deep frying).

Substituting has a predictable direction. Cake made with bread flour comes out tough; bread made with cake flour rises and then collapses.

Faking one from another

• For cake flour: take 15g out of 100g of plain flour and put 15g of cornstarch back. Starch has no protein, so the overall percentage drops.
• For bread flour: about 5% vital wheat gluten stirred into plain flour gets close. Without it, use plain flour and knead longer instead.
• For plain flour: half bread, half cake.

In something like brownies, where flour is a minor ingredient, the choice barely shows. The more the flour is the structure, the more it matters.

"00" is not a protein grade

Italy's 00, 0, 1 and 2 describe how finely the flour is milled, not its strength; protein is stated separately. Some 00 flours are strong pizza flours and others are soft. "00 means tender" is a misreading.

Semolina and durum are a different wheat entirely (hard durum), coarsely ground. They hydrate slowly and bite firmly, which is why dried pasta uses them. Swapped in for flour, you get a different food.

Things sold beside flour that are not flour

• Wheat starch is what remains after flour is washed to remove the gluten — pure starch, no protein, so it cooks clear instead of setting white and opaque. It is the translucent wrapper of har gow, and plain flour cannot do it at any thickness.
• Pure starches (potato, corn, tapioca) are for thickening, not structure (thickening sauces).
• Self-raising flour already contains baking powder, and some bread flours come pre-mixed with yeast. Read the bag.

Storage

White flour keeps well because it has little fat. Wholemeal does not: oil in the bran oxidises and turns rancid within months. Keep wholemeal refrigerated or frozen (freezing and thawing).

White flour still picks up smells, so keep it sealed. Once it tastes bitter or smells stale there is no fixing it.