The safest way to store schmaltz is in the refrigerator or freezer. It will last for several months in the fridge and indefinitely in the freezer. If you plan to use it often, keep it in the fridge. Then, when you're ready to use it, let it rest on the counter for 30 minutes to bring it back to room temperature, or zap it in the microwave for 30-60 seconds to soften.