There are all kinds of emergencies we might experience, some of which require us to leave our homes unexpectedly — think events like severe hurricanes or tornados — sometimes leaving a refrigerator and freezer full of food behind. Upon our return, we might wonder: Is this food still safe to eat? As anyone who has ever had a food-related illness knows, you don't want to take that risk lightly — but that's where the "cup quarter trick" comes in. Indeed, it might actually save your life, or at least prevent you from getting really, really sick.
If you come home after a lengthy absence and find that your power is out, you know that everything perishable inside your fridge has basically got to go. But if you come home and the power is on, how can you tell whether the food is safe? What if, for example, the power went off, the temperature dropped, and then the power came back on, and it appears to be refrozen? That's where the quarter cup trick comes in to save the day (and your stomach).
As Marlisse Cepeda explains over at Delish, the cup quarter trick has been around for a while, but recently went viral due to a Facebook post. As the post explains, all you need is a quarter and a cup for water (as well as some forsight). First, you fill the cup with water. Then, you put it in your freezer until the water is frozen solid. Next, remove the cup and put a quarter on top of the frozen water. Then, put the cup, with the quarter still on top, back in the freezer. Done.
What is this supposed to prove? The idea here is that if you come home and find the quarter still on top of the water, your power likely stayed on and your fridge didn't turn off. Lucky you, your food is probably still safe to eat! If the quarter is in the middle, it's murky territory — it means that your power may have gone out for a time, but then come back on before the ice in the cup fully melted. In this case, use your judgment on whether your food is safe to eat. If you return home and the quarter has sunk to the bottom, though? You can assume your power was off for a substantial portion of time, meaning that your food may no longer be safe to consume. Sad day — but at least you know, right?
While posts from concerned citizens are always useful, it's good to know the actual science behind food safety, too. According to the Food and Drug Administration (FDA), "Refrigerated food should be safe as long as the power was out for no more than four hours and the refrigerator door was kept shut." This makes sense, though if you're leaving because of an emergency, it's possible you won't be home within four hours to check.
The FDA also advises to "discard any perishable food (such as meat, poultry, fish, eggs, or leftovers) that has been at temperatures above 40° F for two hours or more (or one hour if temperatures are above 90º F)." Again, solid advice for the day to day, but tough to monitor if you're gone for an extended period of time. The cup quarter trick, while still relatively imprecise, might give you a better idea of how long your food has been unrefrigerated and whether it fits these guidelines.
If you're curious about how long your fridge and freezer stay cold when the power goes out, know that estimates vary based on your individual unit. In general, however, Foodsafety.gov advises that a "refrigerator will keep food cold for about four hours if the door is kept closed," similar to the FDA guidelines. In terms of your freezer, Foodsafety.gov says, "a full freezer will hold its temperature for about 48 hours (24 hours if half-full)."
As a good rule of thumb, if your food smells bad, has concerning discoloring, or something is just plain off about it, it's best to skip eating it. It might feel wasteful, but food-related illnesses are no joke, so it's best to err on the side of caution.
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