Dear wow: surely you must have many times found that the top of your saltshaker had moist salt clooging the tip so no salt would come out. The same thing would happen to bulk kitchen salt, that's why it was kept in the saltboxes on the shelf above the kitchen stove.
Incidentally, when I mentioned the 49ers making sourdough, I forgot to note that they were for this reason often referred to as "sourdoughs". I am not sure what figure of speech that it.
My wife told me that when she was a girl, she could tell if any neighbor within half a mile was making saltrising bread. When the airborne yeast begins to work, it makes a gas with a very strong but not vile odor, not as pleasing as the odor of regular yeast. But even she did not know the secret, for which all the clues have now been given. It took me twenty years to find a book that mentioned it, so I would be surprised and even a bit chagrined if you could quickly figure it out.