That happened to me once. I just dumped it out, rinsed my grains and started again with a small amount of milk. I never put my kefir in the fridge until I'm ready to start a new batch. When my milk turns to kefir, I get another jar, fish out my grains with a slotted spoon, put my grains in the new jar, add milk to it, set that jar on my shelf and put my kefir in the fridge. I only put my milk and grains together in the fridge if I am going to be away for several days as the cold keeps the milk from turning into kefir so quickly. Hope that helps.....your grains were not contaminated!