No, you don’t have to use Guinness. But I think it really gives the stew a great flavor. You can use whatever beer you like to give the stew extra flavor. I would also recommend using dark beer or ale if you are going to use beer. Something like a stout or porter would be good for that extra richness. If you don’t want to use beer, you can just use beef broth. Another idea is to use water and beef bouillon. I like to keep the brand Better than Bouillon on hand as it has good flavor and keeps well in the pantry.