You can substitute yeast with equal parts lemon juice and baking soda. So if a recipe calls for 1 teaspoon of yeast, you can use half a teaspoon of lemon juice and half a teaspoon of baking soda. Keep in mind that the bread will not need the typical proofing time and the dough will begin rising right away.

To substitute baking soda and acid for yeast in a recipe, replace half of the required amount of yeast with baking soda and the other half with acid. For example, if a recipe calls for 2 teaspoons of yeast, simply use 1 teaspoon of baking soda and 1 teaspoon of an acid.

Baking soda and buttermilk combine to make a good substitute for yeast, particularly in gluten-free baking. The National Library of Medicine says that buttermilk is the best liquid for gluten-free baking due to its high-acid content, as well as because buttermilk can inhibit gluten from forming.