When the mercury drops, sourdough starters become sluggish. The wild yeast and bacteria that power fermentation slow dramatically below 65°F, and many home bakers assume their culture is dead when it's simply dormant. The difference matters: a truly dead starter shows pink or orange streaks and smells like nail polish remover for weeks. A cold one just needs patience. The $3 Heating Solution Instead of buying a commercial proofing box, try a small cooler with a jar of hot water replaced every 4 hours, or position your starter near (not on) a heating vent. Baker's linen and a heavy blanket trapped around the jar can maintain 68–72°F, the sweet spot for winter fermentation. Some bakers swear by placing the jar inside a turned-off oven with the light on. "I've kept starters alive in Montana winters by wrapping them in a heating pad set to low," says James Beard Award winner, Tartine's resident baker. Feed your starter once a week if it's cold-stored, using room-temperature water. The key is consistency—erratic feeding stresses the culture more than cold does. Once spring arrives, your starter will roar back to life.