The difference between bread flour & all-purpose flour?

Jen posed an interesting question in the comments for the Bread Machine White Bread. What's the difference between regular old all-purpose and bread flour? And to be honest with you, I knew there was a difference, but could not tell you exactly what that difference was! Alrighty then!

So off to google I went. I discovered that bread flour is higher in gluten and protein. Both of these are important when baking bread. The gluten is what helps bread become elastic, work with the yeast better, and in the end, makes the loaves chewy and rounded/full. The more elastic the dough, the better it traps the gasses that the yeast creates. When this happens, the dough rises! Voila!

In flour, the higher the protein/gluten, the chewier your product will be. I found this great link showing protein % of flours:

Cake flour is typically 7-9% protein;
pastry, or cookie, ~9-10%;
all purpose, 10-12%,
bread, 12.5-13.5%,
clear and high gluten, 14-15%;
gluten "flour" (actually refined gluten), 45%.

And if you think about it - you dont want a tough/chewy cake or pie crust, right? But you would want a chewier pizza dough or bagel. So that's where the bread flour comes in handy.

I hope this helps answer your question, Jen?? Let me know if it does and if you have any other questions!
PS: 2 good links for reading more on this are Ochef and this site!