When making dried beans, generally I wash the beans, then soak them, then drain&rinse, then cook. I realized today that I started my soak without the prior wash (by accident), and then realized it shouldn't matter; after all, I am going to drain&rinse them post-soaking anyway; that should take care of the wash step, shouldn't it?
tl;dr Do dry beans always need to be washed pre-soaking, or is post-soak ok too?
It's always a good idea to wash and "pick over" a bag of dried beans before soaking them. You never know what sort of grit or weirdness you might find. It's a lot more difficult to find the stuff-that-isn't-beans once it's all been soaking together for a long time.
I don't think there is anything disastrous about doing it in that order. I suppose any impurities might penetrate the membrane of the bean, but the expected impurities (especially if the beans are organic) is just soil. I'd still rinse beans before soaking in general, but if I forgot once, I'd do what you said.
I always wash legumes and grains. This may be gross to consider, but in most elevators and plants dealing with legumes or grains, there is at least one rodent or there is one person using a contaminated shovel or other tool. You never know what is mixed with your cooking ingredient, so it pays to wash just in case.
Just for information's sake: rodent feces and bugs will both float to the top if you dump your grain or legumes into a pot of salt-water, and the salt will also kill most bugs. I always use the salt-water dump-and-skim before rinsing; most times it's not needed, but there have been times I was glad I did it. Additional info: The salt-water dump is also great for getting the bugs out of broccoli and cauliflower.
