Thank you HuffingtonFood for this interesting article!
In the early and mid 1800’s, rural Ireland did not have a strong tradition of yeast bread making. Baking was done in the home and, in addition to having limited supplies, time was often at a premium. The use of baking soda as a leavening agent was quick, effective and it produced a much more consistent result than yeast did. It caught on quickly and made soda breads a staple of the Irish diet until commercial bread production began in earnest, though it is still popular in Ireland and many other parts of the world.
The original soda breads contained nothing more than flour, buttermilk, baking soda and salt. The buttermilk was leftover from the butter making process and the bread was almost always served with freshly churned butter. Today, the breads often contain additional ingredients, like sugar, butter, currants or caraway seeds to enhance the flavor of the bread. Soda bread is heartier than most yeast breads and pairs very well with soups, stews and meat dishes. It also makes outstanding toast.