The first to use magnetic freezing were the Japanese, and they did so to preserve the jewel in the Japanese food crown: bluefin tuna.
Hence, much of the equipment sold in Japan is used for freezing fish. However, they are also used to freeze other everyday foods that are especially sensitive to freezing, such as bakery doughs, sauces, vegetables or sushi preparations.
However, the promising technology of magnetic freezing has not spread noticeably to the Western market. In fact, in Spain only some industries and restaurants interested in improving food freezing have acquired this equipment to test it.
But do they really do what they promise? Do they improve the quality of frozen foods?
In the magnetic freezer, according to its manufacturers, the ice crystals that form on the food are tiny. In this way, the cells are kept intact and the food retains its organoleptic properties after the thawing process.
Industrial secrecy allows these devices to go on the market without showing their technical specifications. So the industries do not know the intensity of the magnetic field or the frequencies they use.
In a very simplified way, it is a forced air freezing device to which a magnetic field generator is attached.
If these magnetic fields are generated by permanent magnets or electromagnets, we would be talking about static magnetic fields. If they are induced using electromagnetic coils, they are oscillating magnetic or electromagnetic fields, continuously or pulsed over time.
A fundamental factor that defines the organoleptic quality of the product (color, flavor, texture, etc.) is the size of the ice crystals that form during freezing.
Large crystals can damage the structure of the food, causing changes in its texture and a significant loss of water during defrosting.
The patents and publications on magnetic freezers ensure that they prevent the formation of exudate, that is, the loss of water after defrosting that worsens the quality of the food. And they achieve this, according to the manufacturers, because the magnetic fields applied during the freezing process orient the water molecules (“vibrate”), preventing their grouping and, with it, the formation of ice crystals.
However, we know that although water has a high dielectric constant, it has a small magnetic susceptibility, that is, it is very insensitive to magnetism. This contradicts the physical foundations on which magnetic freezers claim to be based.
The results published in various scientific journals supporting this technique are confusing and sometimes even contradictory.
In order to reach significant conclusions, more rigorous studies are required to guarantee the reproducibility of the results.
It is essential that the effect of freezing be compared in the presence and absence of magnetic fields, under the same processing conditions (air speed, freezing temperature, etc.) and with an appropriate group of samples, both in terms of their number and due to its size, shape and composition.
The first step to put them to the test was to thermally and electromagnetically characterize these devices. To do this, we measure the temperature, air speed, magnetic field intensity and frequencies at different points on the freezing trays.
Once the specifications of the magnetic freezer are known, we carry out controlled experiments, applying the same freezing temperature and air speed, with different magnetic fields.
They have been tested on food models (water, sodium chloride and ferric chloride solutions, dispersions of magnetic nanoparticles) and on different real foods.
In the laboratory, we have applied static magnetic fields, low-field alternating electromagnetic fields and a combination of the previous two, which are those that exist in some of the commercial equipment. In none of our studies have we observed an improvement in the quality of frozen foods.
After thawing, the water retention capacity was not maintained in either frozen pork loins or crab sticks with very weak oscillating magnetic fields (0.04-2 mT at 6–59 Hz).
Nor did it reduce water losses either in chopped muscle of frozen fish with application of weak oscillating magnetic fields (7 mT at 50 Hz) or in frozen potato pieces with high static magnetic fields (150-200 mT).
If magnetic fields were responsible for all the advantages that the manufacturers of these freezers claim, this new technology would have spread around the world and would represent a significant advance in freezing technology. Not only for food preservation but also for cryopreservation of biological samples, such as cells, tissues and organs.
So far it seems that the high price of this equipment is not justified, since scientific evidence indicates that the positive effects found on the quality of the food are fundamentally due to the result of the powerful mechanical cold system (-50 °C vs. -30°C) and not to the benefits of magnetism.
This article was originally published on The Conversation.
Miriam Pérez-Mateos has participated in the 2013-2016 research project on "Characterization of electromagnetic freezing in food matrices".
