What provides the acid for leavening in this banana bread recipe? I have made this banana bread recipe a couple of times. The ingredients are:


All-purpose flour
Salt
Brown sugar
Baking soda
Bananas
Butter
Eggs


My understanding is that baking soda requires some acid such as milk or yogurt to provide leavening. But this recipe doesn't call for anything that is an acid that I can see. Yet it does produce a perfectly edible loaf and not a dense brick. 

What is reacting with the baking soda to provide leavening?
Most of the ingredients in this recipe are acidic. 

ph values:


flour 5.5-6.5
brown sugar slightly acidic
bananas 4.5-5.2
butter 6.1-6.4


The salt is neutral and the eggs are not acidic, ph 7.1-7.9

The combination of these ingredients is acidic enough to interact with the baking soda to leaven the bread. 

Even without the bananas, there would be some leavening. Consider the standard ingredients in chocolate chip cookies: flour, sugar, butter, eggs, salt, baking soda and chocolate chips. Though they don't raise nearly as much as banana bread, they do poof up a bit.