Hi: I just tried making mashed sweet potatoes for the first time. They were delicious, but at least one of the potatoes was pretty stringy, and some of the strings were quite fibrous. I know if you use a hand blender to mash them the strings will wrap to the beaters, but I don't have one and I'd just assume mash them with a fork. I'm not really looking for a puree, anyways. So, is there any trick to picking good potatoes? One website said avoid the huge ones, one said to avoid "grunts", and another said to avoid the "gnarly" looking ones. That seems like I'd be avoiding them altogether. Any help?