Making delicious, chewy french baguettes without yeast? Baking powder?!

Yes, in the sense that you do not need to buy yeast if you use a sourdough starter / levain / chef / levito naturale.  In that case, you are using a wild yeast and bacteria culture that you maintain for leavening purposes.

No to the idea of using a chemical leavener, such as baking powder or baking soda.

In over-simplified terms, bakers use yeast because yeast produces carbon dioxide gas, which is trapped in the gluten network of the dough, inflating all of those tiny to large bubbles in the dough.  For the purposes of this discussion, we can say that yeast has no appreciable influence on the chewiness or tenderness of the bread.

The chewiness in baguettes or other breads comes from the gluten in the dough.  In wheat flours, gluten is composed of two proteins, glutenin and gliadin, that combine in the presence of water.  If you were to wash the starch from the gluten in the flour, the remaining ball of gluten would be a sticky, elastic mass.  That combination of stickiness and elasticity allows the gluten to be stretched into thin membranes that form the walls of the alveoli, or bubbles, in the dough. 

At this point you might well ask "So why not use baking powder?  It produces carbon dioxide gas and inflates the bubbles, too!"  Fair enough.  One reason is that a bread leavened with baking powder has a different flavor than a bread leavened with commercially produced yeast or wild yeast.  Another reason is that even more flavors can be teased from the flour through extended fermentations; since baking powder relies on a simple chemical reaction instead of fermentation, the resulting bread will comparatively flavorless.  Perhaps the most important reason is that yeasted breads rely on either extended mechanical working of the dough (via hand or machine mixing and kneading) or on extended time with minimal working of the dough, to allow full development and organization of the gluten in the dough.  The amount of time required for either approach is enough to greatly degrade the leavening capabilities of the baking powder, since some of the chemical reactions will begin as soon as the baking powder contacts the moisture in the dough.

Many, though not all, breads that utilize chemical leaveners such as baking powder start as batters, instead of as doughs.  Muffins and quick breads, such as banana bread, tend to fall into this category.  Other, stiffer doughs, like scones and biscuits, demand that gluten development be kept at a minimum to ensure tenderness.  All of them go into the oven as quickly as they are mixed and shaped.  Although I had not thought of it in this context previously, I'm not sure that baking powder would have sufficient leavening capacity to overcome the resistance (elasticity) of the gluten that is developed in baguettes and other breads.

I hope this helps.

Paul

Yes with a sourdough levain and no with baking powder.