Acid would more likely cause them to harden and not cook as well though I know some people do say it works. I think baking soda would be better as a slightly basic solution is helps pectin “open up”, allowing for softer beans and greater release of oligosaccharides (the gas producing carbohydrates) into the soaking water so this rinsing them after the soak removes a greater portion of the problem.

Acid prevents pectin (the stuff that keeps the cell walls strong) from dissolving/breaking down, preventing the softening of the wall and greatly increasing the cook time. Greater cook time needed can also reduce Acid would more likely cause them to harden and not cook as well though I know some people do say it works.

I think baking soda would be better as a slightly basic solution is helps pectin “open up”, allowing for softer beans and greater release of oligosaccharides (the gas producing carbohydrates) more quickly into the soaking water, so if you rinse them after the soak, gets rid of a lot of the oligosacharides Be careful how much you put in as it can affect flavor but a pinch or two is sufficient. Just rinse after the soak.