What are the differences between Cake, Bread and Pastry flour?

Flour for cakes and biscuits has lower protein content than bread making flour and is milled from soft wheat varieties. The protein needed to form the structure of cakes and biscuits is not from the flour used but from other ingredients such as egg. Use of cake flour gives a tender soft product as the gluten in the flour does not contribute significantly to the cake structure. If flour that is too strong is used the resultant cakes will be tough and dry and biscuits will not spread out when baked.
Bread making flour is made from semi-hard wheat with a medium to high protein content. This type of flour is referred to as strong flour. When water is mixed into the flour two of the flour proteins combine to form gluten. It is gluten which forms a network that will stretch as the dough ferments and carbon dioxide gas is released. On baking this stretched gluten network sets to give the structure and texture of bread. Strong flour is needed to ensure that sufficient gluten is formed to produce bread of good volume and appearance.
Puff pastry should also be made from flour with high protein content as it is the water absorbed by the gluten that, with the folded-in fat, forms the layers and makes the pastry puff up during baking. For pastry, use the same type of flour that would be used for making bread.

Comparison of flours (values from Composition of NZ Foods 1994)
  White bread flour Cake & Biscuit Flour Pastry Flour
Protein 10.5-13% 7.5-9% 9.5-12%
Starch 75.8% 77.5% 72%
Fibre 3.5% 3.2% 4%
Minerals Range of vitamins incl B1,B2, B3 and folate