I almost 100% sure there is no way to verify something is yeast without a good microscope and other expensive gadgetry. A couple days ago I made some agar wort and put it in petri dishes to collect some local yeast cultures. I have one dish that has what I believe to be yeast on it, but I wanted to let the experts take a look and give me a recommendation. Without a microscope I know the only way to know is to build it up and brew with it, but I'm just hoping for someone to tell me whether or not I am wasting my time. Thanks.