I love jicama raw or sticks tossed in lime juice & chili (one of the few pleasures allowed on this diet). But, sometimes I get a good sweet crunchy white interior jicama & sometimes it's kindof slimey, darker or not sweet at all. Does anyone know how to tell a good one? Also, how long can you refridgerate without peeling? You'd think with that thick dark yucky skin they would keep forever, but it seems like anything past a couple of days never slices up to something I want to munch on. Any jicama specialists out there to help me?