Why would you use baking soda when cooking beans?

Hard water yields hard beans; adding sodium bicarbonate or baking soda to the cooking water for beans softens the water, thereby increasing the tenderness of the beans. Use 1/4 teaspoon of baking soda for each pound of beans.

Adding baking soda is recommended for older beans that are drier and harder to cook. For fresher dry beans, adding baking soda may cause mushiness, because it over-softens the water. Use the freshest dry beans whenever possible, as older beans that have been stored away for too long or in less than ideal conditions may never become soft, with or without baking soda.