The short answer to the question in the title is “It isn’t essential at all.” All-purpose flour works just fine. I’ve even tried mixing cake flour with all-purpose flour too. There is a caveat, of course. The length of kneading time and the texture of the baked bread are affected by the flour or mixture of flours used.
One word explains everying — gluten. The amount of gluten in bread flour is high; the gluten in cake (pastry) flour is low. As a result, bread is chewy while cakes are crumbly.
The addition of yeast to bread dough, the kneading and the proofing are all meant to “agglomerate” the gluten to make the dough elastic so that the bread is chewy after baking. Dough made with bread flour requires less kneading because the gluten content of bread flour is high. As the gluten content of the flour used becomes lower, the longer the kneading time that the bread dough will require to reach the level of desired elasticity.
All that is not theory. All that is what I’ve observed after baking several batches of bread. To illustrate, the bread in these photos were made with all-purpose flour. I used the old basic bread recipe in the archive AND a stand mixer. I mixed all the ingredients with half of the total amount of flour by hand then I switched on the mixer to “KNEAD” (the lowest setting). With the motor running, I added the rest of the flour little by little, scraping the bowl every five minutes. The total kneading time was 20 minutes.
I let the dough rise until doubled then I rolled it out into a rectangle. Leaving a half-inch margin on all sides, I spread the entire surface of the rolled dough with the simplest version of my homemade pesto with no nuts. Next came the grated cheese. A mixture of sharp cheddar and mozzarella was my choice for this bread.
I rolled the dough and pinched the edges to seal. Then, I cut off the two ends and discarded them. The remaining dough was cut into twelve equal portions, each about two and a half inches in length.
The cut dough were arranged, two inches apart, in a baking pan lined with non-stick paper. The pan was covered loosely with cling film and the dough was left to rise a second time.
After some 25 minutes of baking at 375F, this was how the bread looked. The dough expanded during the second rising and it expanded even more — quite tremendously, in fact — during baking. The cheese got toasted in the process creating a bright red spiral that interspersed with the greenness of the pesto.
Just so it’s clear — these bread rolls were made with all-purpose flour. No bread flour at all. The outside, although nicely browned, was not as crusty as they would have been had the dough been made with bread flour. But the inside was wonderfully soft and moist, and the grain was quite fine — finer than the grain of bread made with bread flour.
My conclusion? The longer kneading time is well worth the trouble. Bread made with all-purpose flour is just lovely.