Using All-Purpose Flour + Cornstarch Instead of Cake Flour
Ratio
For 1 cup cake flour: use 1 cup AP flour minus 2 tbsp, add 2 tbsp cornstarch
Excellent — nearly identical results
Measurement Variance Note
For 1 cup references, this ingredient can vary by about 12% across brands and measuring methods (100g-128g per cup). For the most reliable substitution result, measure by weight and test a half batch first.
What changes when you swap cake flour for all-purpose flour + cornstarch
Swap two tablespoons of cornstarch into every cup of AP flour and you knock the effective protein down from around 11% to roughly the 8% range cake flour lives in. That dilution is the whole game in a tender layer cake or hot milk sponge — fewer gluten-forming proteins, more pure starch to absorb sugar and fat, and a crumb that compresses softly under a fork instead of springing back like a muffin top.
- Sift the AP-cornstarch blend three times before measuring — without it, the cornstarch settles in pockets and you get pale streaks of starch slurry inside an angel food cake.
- You miss the chlorination that real cake flour gets, so the crumb runs a half-shade tanner and absorbs about 5% less liquid than a Swans Down sponge would.
- For chiffon cakes or genoise leaning entirely on whipped-egg structure, the swap holds; for a 1-2-3-4 pound cake where butter does most of the lifting, the difference is barely perceptible.