Why put a penny in the freezer?

Why put a penny in the freezer? Putting a penny in the freezer is trick to check if freezer lost power and food thawed while you were away, often called penny in cup trick. Method is fill cup with water, freeze it, then place penny on top of ice and leave in freezer. If you return and penny is still on top, freezer stayed frozen. If penny has sunk to middle or bottom, it means ice melted and refroze, indicating freezer was without power long enough for food to thaw, so food may be unsafe and should be discarded. It is simple low tech power outage detector, useful when traveling or during storms. It works because coin will sink when ice melts. Some people use quarter. It does not prevent anything, it just tells you if thaw occurred. It is especially useful for detecting if meat or other perishable thawed and refroze which could cause food poisoning. So putting penny in freezer is safety check for power outage.