Freeze food is a technique to prolong their duration. However, in the case of fish intended for raw consumptionas in the case of sushifreezing does not only serve to preserve it but also to break down the microbial and parasitic charge chargein particular theAnisakisa microorganism dangerous for the human being. When we comply with a fish, we comply with the water present in its cells, through a process called nucleation that then leads to the formation of ice crystals. In the domestic freezer, the temperature drops slowly, forming a few but Large crystals which can break cell membranes, damaging the fabric of the fish. The deception, on the other hand, cools much faster through a ventilation system, creating many small crystals that do not damage the cells, preserving the quality of the food. Regulation (EC) 853/2004 requires raw fish to be frozen at -20 ° C for at least 24 hours to guarantee their safety.
Freezer freezer: what are the differences
When we join a fish, in reality we are freezing billions of microscopic Drops of water which are inside its cells. This process takes place in several phases, with the formation before small point crystals (nuclei), hence the name nucleationwhich then increase to become larger crystals (crystallization). The difference between the freezer and the boss lies in the cooling and training speed of the crystals.
The domestic freezer (also called freezer) it is designed not so much to quickly lower the temperature of the food, but rather to maintain a low and stable temperature over time. The refrigeration takes place in a way relatively slowand the temperature of the water inside the cells gradually descends: so few initial nuclei are formed to which the water molecules aggregate to them by increasing them. The result is the formation of a few but large ice crystals (macrocrystals), which can push against cell membranes, until they break them. This can lead to damaging the tissue and compromising the quality of the food, especially during the defrosting in which the water, returning liquid, will drop outside. In addition, there will be greater exposure to contaminants (such as bacteria or mushrooms), which can penetrate more easily inside the fish cells.
THE’temperature delayer It is a equipment used mainly in the catering sector. Unlike the domestic freezer, it is designed to cool foods in times extremely quick: this happens thanks to a forced ventilation system which accelerates the thermal exchange with the food. The speed of the process allows you to form many nuclei: the water molecules do not have time to join in large ordered structures, therefore smaller crystals are formed (microcrystals) that do not damage cell membranes, preserving the structure of the fabric and the quality of the food. Also for this reason, the deception is the favorite tool to safely keep delicate foods such as raw fish intended for consumption.
Because raw fish must be frozen first
Freeze a food not only serves to keep it longer (cryoconvation): In the case of raw fish, such as the one used for sushi or sashimi, freezing is also a treatment of food safety. It serves to delete or drastically reduce the presence of parasites such as theAnisakissmall nematode worm that can nest in the bowels and flesh of the fish. Once ingested alive, it can in fact cause even serious gastrointestinal disorders in the human being, a condition known as anisakidosis.
Often, when it comes to food, the main way to decrease the bacterial or parasitic charge consists in the use of high temperatures (as happens in the pasteurization of milk). But in this case one high temperature The fish would cook, then low temperatures are used: the fish must be frozen and subsequently defrosted in the refrigerator, in line with the indications of theEfsa (European Food Safety Authority).
What experts say
According to the Regulation (EC) n. 853/2004the fish destined to be consumed raw must be frozen a -20 ° C for at least 24 hours To guarantee its safety, as reported an order from May 1992 of the Ministry of Health. The use ofdelayer Especially in the professional field, it allows you to quickly reach the required temperature, improving the effectiveness of the treatment.
In the house, where you often do not have access to a boss, it is important to carefully follow the indications of the health authorities. THE’Efsa Also remember that, to avoid Crusader contaminationsit is a good practice to keep the foods raw from those cooked or ready to consumption separate, both in the freezer and in the refrigerator.
