when I make a scratch cake, I use whatever the directions say to use. You can substitute one for the other but it's not a one-to-one substitution. I don't know the formula for making the substitution.
The difference between the two is cake flour is lighter, softer, and pre-sifted compared to AP flour.
Here is a substitution chart that I posted a couple weeks ago.
http://www.cakecentral.com/cake-decorating-ftopict-50415-substitution.html+chart
the differences in flour is the percent of protein the flour contains...cake flour has less protein than any other flour, therefore making it lighter, softer, and more tender of a product..
when you mix flour with water, gluten strands form, and the more protein in the flour, the higher gluten forming potential they have. gluten is responsible for the volume, texture and appearance of baked goods..without gluten, baked goods could not stay raised.
cake flour 6-8 % protein tender cakes
pastry flour 7.5-9.5 % protein biscuits, pie crusts
all-purpose flour 10-13 % protein general baking
bread flour 12-15 % protein yeast breads
whole-wheat flour 13-14 % protein breads
high gluten flour 14-15 % protein bagels
you should use that the recipe indicates most of the time though!
hth
yes, normally it will state cake flour in all the recipes I have run across if they mean cake flour.
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