There seems to be a wide gap between common understanding of the way that the world works, naive or folk science if you wish, and reality. This calls into question the effectiveness of science teaching, and whether consumers are being adequately protected from their own gullibility.
Today’s example is a device sold widely as a “miracle thaw defrost tray” by various suppliers, often through major online retailers who really should know better. My concerns are not only that this product is largely ineffective and its claims rely on consumer naivety, but that it has potential health risks. Shame on anyone selling such products.
The reality is that this is an aluminium tray covered with a black low-stick coating. That is not much for the money being asked – typically £12 to £15. It is claimed to “defrost food quickly and safely” by a process not specified which “absorbs natural heat and energy in the air and then releases it directly into the food.”
The implication of “absorbs natural heat and energy in the air” is that this tray somehow becomes warmer than a different tray might, because it somehow gains more heat and energy from ambient air. That is arrant nonsense and non-science (see the laws of thermodynamics).
Because the tray is black and not shiny and white, ambient radiant heat will lead to its warming above ambient air temperature. Leave it bathed in sunshine from your kitchen window, and its surface will become quite warm. If you then place frozen food on it, it will initially defrost the food more quickly than the cooler surface of a lighter-coloured reflective tray would.
The snag is that, far from the tray somehow magically (or miraculously) channeling heat and energy from ambient air into the defrosting food, the cold food cools the tray, and by covering its surface, blocks radiant heat. Once the tray under the food has been cooled close to the temperature of the food, defrosting becomes very slow.
Furthermore, more than half of the surface area of the food is not in contact with the magical tray, but surrounded by ambient air. The rate at which it defrosts is therefore dependent not on the properties of the tray, but how warm your kitchen is. Again, if you leave the food in a warm area, it will defrost more quickly irrespective of the tray.
So any potential reduction in time to defrost resulting from the use of this tray – as opposed to any other tray – is likely to be small, if significant at all. Compared to the time required to defrost in a modern good-quality microwave oven, using the tray will take much longer. Always. Compared to the time required to defrost in a fridge or similar cold place, the tray will always be quicker, but so would any tray used out of the fridge.
Against that we must weigh the requirements for food hygiene. Leaving food lying around in the open air of your kitchen for the long periods required to defrost is not a practice which should ever be encouraged. The risk of flies settling on the food is substantial, and once temperatures in the food exceed 4˚C or 5˚C bacteria on and in the food will start to multiply. This is particularly important as defrosting without microwaves proceeds from the outside in, so there will be substantial periods over which the outer layers of the food will be at temperatures sufficient to support bacterial growth, but the inside of the food is still frozen.
Using this tray to defrost chicken, other poultry, fish, or any foodstuff which will not be cooked thoroughly, is an open invitation to food poisoning and illness. Although putting a fine-grilled cover over the food will reduce the risk of flies settling, it will also slow defrosting and further reduce any marginal benefit of this “miracle” device.
If you do not believe me, try here, here, here, here (p 17), here, and in many other places. Indeed, if some of these online retailers were to peek in the books that they sell, they would see the message written clearly in those too.
Not only does this beg questions of the ethics and legality of anyone offering such products for sale, but it shows the actual value of customer reviews – overwhelmingly and naively positive – and reveals how few people understand basic everyday physics.
It is of course possible to warm objects up above (or to cool them down below) ambient temperature. But to do so requires energy and mechanism. Perhaps we are so used to incredible claims of ‘new’ technology, or science fiction, that we are unable to spot what is not physically possible. This is a sad indictment of fact-packing in school science, rather than the attainment of understanding.
Meanwhile I have ordered several thousand of these. I reckon that if I can cascade their absorbence “of natural heat and energy” in series, I should be able to boil water, get that steam to drive a turbine, and then generate electricity. That is a real miracle – power from black aluminium trays – worthy of a Nobel prize. Pass the snake oil, please…