This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
The gingerbreads containing the largest proportion of soda are darker in color. This is due to several factors, i.e., the effect of the soda on the color of the flour, the decomposition of the monosaccharids of the molasses by the soda, but principally to the color produced by the tannins of the molasses in an alkaline solution. The gingerbreads with baking powder and soda are lighter in color. The flavor of the gingerbread made with baking powder and no soda is different from that of gingerbread containing soda, particularly when a strong molasses is used, probably because the soda combines with some of the ingredients of the molasses, thus producing a less strong flavor. With excess soda, its soapy, alkaline flavor is evident.