Do you flatten aluminum soda or beer cans before tossing them in the recycling bin? You shouldn't, and here's why: Many recycling facilities use automatic sorting machines that separate two-dimensional and three-dimensional items from co-mingled recycling bins. When you flatten a soda can, the sorting machine will often mistake it for paper. And when metal gets into paper recyclables, it can contaminate a whole load. But the good news: There's no need to be super careful about recycling perfectly round cans. Even dented and slightly crushed are fine. But totally flat cans should be left out of the recycling bin altogether.