Magnetic freezing is nowadays established as a commercial reality mainly oriented towards the food market. According to advertisements, magnetic freezing is able to generate tiny ice crystals throughout the frozen product, prevent cell destruction, and preserve the quality of fresh food intact after thawing. If all these advantages were true, magnetic freezing would represent a significant advance in freezing technology, not only for food preservation, but also for cryopreservation of biological specimens such as cells, tissues, and organs. Magnetic fields (MFs) are supposed to act directly on water by orientating, vibrating, and/or spinning molecules to prevent them from clustering and, thus, to promote supercooling. However, many doubts exist about the real effects of MFs on freezing and the science behind the potential mechanisms involved. To provide a basis for extending the understanding of magnetic freezing, this paper presents a critical review of the materials published in the literature up to now, including both patents and experimental results. After examining the information available, it was not possible to discern whether MFs have an appreciable effect on supercooling, freezing kinetics, ice crystals, quality, and/or viability of the frozen products. Experiments described in the literature frequently fail to identify and/or control all the factors that can play a role in magnetic freezing. Moreover, many of the comparisons between magnetic and conventional freezing are not correctly designed to draw valid conclusions, and wide ranges of MF intensities and frequencies are unexplored. Therefore, more rigorous experimentation and further evidence are needed to confirm or reject the efficacy of MFs in improving the quality of frozen products.

Since the earlier 2000s, electromagnetic freezers have been sold all over the world. According to the manufacturers, the oscillating magnetic fields (OMFs) applied by these devices are capable of avoiding ice damage in frozen foods. To assess the effectiveness of OMFs in preserving food quality, we froze crab sticks in a commercial electromagnetic freezer, both with (<2 mT, 6-59 Hz) and without OMF application. Crab sticks were also frozen in a conventional freezer, both with static-and forced-air conditions, to compare electromagnetic freezing with conventional methods. After 24 h and 1, 3, 6, 9, and 12 months of storage, we did not find any effect of the OMFs on the drip loss, water-holding capacity, toughness, and whiteness of the crab sticks frozen in the electromagnetic device. Moreover, no advantage of electromagnetic freezing over air-blast freezing was detected at the conditions tested. More experiments at larger magnetic field strength and wider frequency ranges are needed to have a complete view of the potential effects of OMFs on food freezing.

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Previous papers in the literature show no agreement on the effects of static magnetic fields (SMFs) on water supercooling and freezing kinetics. Hypothetical effects of the SMF orientation and the presence of ions in the sample are also unclear. To shed light on this matter, we froze 10-mL pure water samples and 0.9% NaCl solutions subjected or not to the SMFs generated by two magnets. We found that the relative position of the magnet poles affected the magnetic field orientation, strength, and the spatial magnetic gradients established throughout the sample.Thus, the SMF strength ranged from 107 to 359 mT when unlike magnet poles faced each other whereas it ranged from 0 to 241 mT when like magnet poles were next to each other. At both conditions, we did not detect any effect of the SMFs on the time at which nucleation occurred, the extent of supercooling, and the phase transition and total freezing times in both pure water and 0.9% NaCl solutions. More experiments, under well-characterized SMFs, should be performed to definitively evaluate the ability of SMFs in improving food freezing.

formation nor the potential improvement in the quality of the frozen product has yet been totally clarified.Water is a dipolar molecule and, therefore, when subjected to an electric field (EF), molecules are oriented, lining up their molecular dipoles along the direction of the field. This wellknown effect could be a solid starting point to explain the effects of EFs on water freezing. However, things get a little more complicated when looking for arguments to explain the potential effects of magnetic fields (MFs) on water freezing. Water has no net magnetic moment. When subjected to an external MF, the orbital motion of electrons is altered in such a way that the induced magnetic moments oppose the external field and water is, therefore, a diamagnetic substance. The magnetic susceptibility of water, that is, its magnetic response to the applied MF, is rather low (χ v = −9.035 × 10 6 ) and, therefore, little effects of weak MFs must be expected on water.It is, therefore, in some way striking that, nowadays, the only electromagnetic freezers existing at the market are those that generate magnetic fields, and not EFs, to assist the freezing process. This has happened even though the effectivity of MFs in improving freezing has not yet been proved. Several companies have patented and/or marketed freezers that apply different types of MFs to tentatively improve the quality of frozen food. Such is the case of ABI Co., Ltd. (Chiba, Japan) that sells BCAS (Cells Alive System) freezers^that combine static and oscillating MFs. On the other hand, Ryoho Freeze Systems Co., Ltd. (Nara, Japan) commercializes BProton freezers^that use static MFs and EM waves [1,50]. These innovative freezers actually consist of a MF generator attached to a conventional quick-freezing unit. Additionally, in Proton freezers, an EM wave generator is also added. Depending on the application, the MF or the EM waves may be ceased after certain Bsupercooling period^to quickly induce the immediate freezing of the product, or they may be kept throughout the whole preservation period for a better control of the crystallization mechanism [41]. Many videos that publicize the benefits of both CAS and Proton freezers can be found on the Internet [37]. According to commercial advertisements, both CAS and Proton freezers are able to generate tiny ice crystals throughout the whole frozen product. Besides, they are claimed to prevent cell destruction and preserve the quality of fresh products intact after thawing [1,17]. Consequently, many food processors, restaurants, hotels, hospitals, and research centers, not only in Japan but also all over the world [19,23], have acquired these magnetic freezers. Different food products such as fish (tuna, salmon, or cod, among others), sea urchin, shrimps, sashimi grade seafood and sushi, meat (Wagyu beef, Sufflok lamb, or duck, for example), foie gras, fruits (green mango, lychee, and so on), delicate doughs, and milk products are nowadays magnetically frozen and commercialized as superior-quality food products. Freezing...