Soda bread uses a chemical leavening, meaning it is risen by an acid-base reaction (soda refers to the base used — baking soda) and is different from traditional bread that uses sugar and yeast (single cell organisms) to produce carbon dioxide gas and ethanol (drinking alcohol). Neither one I would imagine sounds appealing to the home cook, but are critical for fluffy, good baked goods. Both work well and have their own set of pros and cons.
Chemically leavened bread does not require time to rise. The reaction starts immediately upon mixing with water and continues while baking; therefore, the dough must get baked shortly after mixing. Soda bread, however, requires immediate baking or the reaction ends and looses the lift before baking. Buttermilk contains lactic acid which reacts with the baking powder (sodium bicarbonate). Baking powder is added also for additional rise, which never hurts in gluten-free baking (notorious for being dense). Baking powder consists of a perfect balance of a protected acid of tartaric acid in form of a salt and sodium bicarbonate (baking soda) that react once it hits moisture. Another by-product of this acid-base reaction is salt, thus the salt in the recipe is minimal.
Soda bread lends itself to a more hearty and wholesome bread than a traditional yeast bread. As you'll see in my recipe, I added millet for the sweet cereal flavor it imparts and kept that heartiness of the bread with the addition of brown rice flour and flaxseed meal. Flaxmeal also creates this wonderful gel, which aids in building structure in gluten-free bread as well as adding omega-3 amino acids. I tried to make this bread without the use of any gums, but to no avail.