The difference between cake flour and pastry flour is that cake flour contains less protein than pastry flour. The amount of protein in a flour changes the turn-out of the food that the flour is used in, due to the fact that protein promotes gluten creation.
Cake flour's protein content ranges from 5 to 8 percent (but can be 7 to 9 percent). Cake flour has the lowest protein content of all flours.
Pastry flour's protein content ranges from 8 to 9 percent.
Food made with pastry flour has a more pronounced texture than cake flour.
Cake flour contains more starch than protein, and food made from it is more delicate and tender.
Both cake and pastry flour are made from soft wheat, but cake flour is chlorinated (with chlorine gas) to chemically change it.
Though neither is suited for breads and can be used for such things as pastries, cookies, quick breads, and brownies, cake flour is better for recipes with a high sugar-to-flour ratio, as the food it is made with will be less likely to collapse after rising.
To achieve a flour resembling pastry flour, cake flour and all-purpose flour, whose protein content ranges from 9 to 12 percent, can be mixed.