Coin In the Cup: RISKY
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Collapse ▲I’ve written about this before, but I want to share again about a food safety podcast that I listen to frequently. It’s called Risky or Not. This podcast is produced by two
Extension Food Safety Specialists, our own Dr. Ben Chapman from NCSU Cooperative Extension and Dr. Don Schaffner from Rutgers in New Jersey.
There are three episodes of Risky or Not every week and each are only about 10
minutes long. In each podcast Drs. Chapman and Schaffner address one food safety
topic, frequently it’s in response to a question that has been asked by a listener or an
Extension colleague. Usually, the question is related to food, cooking or food
preservation or storage. They look at research and the science and give their rational
for deciding if it is risky or not.
I was really excited last week when a question I submitted to the specialists was the
topic of one of their podcasts.
My question was about the putting a coin on top of ice in a cup in the freezer to determine the safety of food after a power outage. I frequently see this tip posted on the internet and I know a lot of people say it works. But I wanted to know from these food safety experts if this is risky or not.
In case you haven’t heard of this, the tip suggests putting a cup of water in the freezer. Freeze it solid and then put a coin on top of the ice and leave in the freezer. The concept is when you come back from evacuation you can tell if the freezer thawed out and refroze while you were gone. Supposedly, if the coin has fallen to the bottom of the cup, it means the food thawed. But if the coin is either on the top or in the middle of the cup then the food may still be safe.
Both specialists say that using this method to determine the safety of the food in the
freezer is: RISKY
Like many people when they first hear this tip, Dr. Schaffner said he thought it was a
good idea. Intuitively it makes sense, but after some discussion, he changed his mind.
The problem with this theory is that ice is less dense than water– so it floats. A coin
sitting of top of the ice will stay on top, too. It’ll be a coin setting on top of a little
iceberg. It is possible that a cup of ice could melt substantially and refreeze and the coin would still stay on top—this would give a false sense of food safety.
The only answer the coin trick gives you is if the ice melts completely and the coin falls to the bottom of the cup before the water refreezes. In this situation you know that the freezer (and your food) thawed. Even then you don’t know what the actual
temperature was inside, so you don’t really know the safety of the food. If the food
stayed below 41 degrees F it would be safe to eat.
There is a solution that is much more scientific and technology based. Drs. Schaffner and Chapman suggest getting temperature loggers. These devices will record the
temperatures within the freezer. Some need Wi-Fi and Bluetooth and you can track the temperature where ever you are—as long as the power and the internet are working. But there are others that don’t need Wi-Fi and can store the data and you can look at the numbers when you get back. Prices of these vary based how much technology you get.
The professors also talked about gel temperature strips and dots. These are less
expensive, but can’t tell you as much as temperature loggers. These indicators stick to surfaces and change color when specific temperatures are reached or surpassed. They are frequently used in food manufacturing to determine if food has reached an unsafe temperature during transport. These can be non-reversable and once the color changes it does not change back, even if the temperature changes and it refreezes.
If you’d like to hear more details on determining the safety of food in your freezer, I suggest you listen to the podcast. Go to Riskyornot.co (yes that is co not com). Episode #775 Coin in Cup for Freezer Safety After Power Outages.
If you have a specific question, you can also send it to the specialists. Who knows, it
might get answered like mine did.
Resources
- McDowell County Cooperative Extension – Food Safety After a Storm
- MSN: Putting a Cup of Ice With a Coin on Top in Freezer?
- Snopes: Putting Coin On Top Cup of Ice?
- Risky or Not?
Syracuse is a Family and Consumer Science team member and can be reached at N.C. Cooperative Extension, Brunswick County Center 910-253-2610 or by email at
clsyracu@ncsu.edu