Protein Matters

• The main difference between all-purpose and bread flour is protein content. Wheat has a protein content that ranges from 5 percent to 15 percent, so the flour industry established labeling standards that point you to the right flour for what you're baking.
  
  

What's All the Gluten About?

• The other big difference between the two is the gluten content. Gluten is the stuff that gives bread its loft, chewiness and elasticity. When you pull uncooked dough apart, the gluten in the wheat is what makes those stretchy strands of elastic dough.
  
  

All-Purpose Flour

• All-purpose flour has less protein and usually a little less gluten than bread flour. That lower percentage of protein makes for softer flour. Use all-purpose flour in pie crusts, cookies, cakes and biscuits and get a more tender baked good.
  
  

Bread Flour

• Bread flour's higher percentage of protein makes it a harder, or stronger, flour to bake with. This is good if you want bread with a chewy, thick crust. Bread flour reacts best with yeast to make bread, rolls, pizza crust and other yeast-risen baked goods.
  
  

The Bottom Line

• You can substitute all-purpose flour for bread flour, but know that the intended results won't be the same. You won't get the loft or chewiness that bread flour will give you. And if you switch out bread flour for all-purpose, you can expect a tough, chewy product, which might make your finished product not as you hoped.