There are five main factors affecting the impact of quick freezing of food

2021-04-22 09:49:00

The temperature of liquid nitrogen used can reach -196℃, and it can take away heat faster when it comes into contact with food. This ultra-low temperature and high heat exchange rate achieve true rapid freezing. Such rapid freezing produces small ice crystals, helps maintain the texture of the food, prevents the loss of water, achieves no loss, and maintains the original color, flavor and quality of the food to a greater extent. That is to say, it ensures that the various changes of the food have reached a greater reversibility during the food freezing process.

With the further improvement and development of liquid nitrogen quick-freezing technology, liquid nitrogen quick-freezing machines are quickly and widely used in fish, shrimp, crab, shellfish, chicken, duck, meat (cattle, sheep, etc.), fruits (bayberry, lychee, etc.), Vegetables, and various prepared foods (steak, sashimi, meatballs, fried shrimp, meatloaf, hamburger, pizza, egg products, soup, etc.) are frozen.

Food contains two kinds of water, one kind of free water, its ice crystal formation stage is between 0 and -5 degrees, and one kind of colloidal water, which is attached to the surface of food molecules, and the crystallization rate is 95% when the frozen product is -18 degrees. the above. In addition, storing food in a low temperature environment after ice crystallization inhibits microbial activity and reproduction, and achieves the purpose of long-term storage and preservation (fruits and vegetables inhibit respiratory heat).

　　 There are five main factors affecting the impact of quick freezing of food:

　　 1. Cooling medium temperature: The freezing speed and freezing point of food are proportional to the temperature difference Δt of the cooling medium. The lower the temperature of the cooling medium, the faster the freezing speed.

　　 2. The influence of freezing products on the wind: the wind surface area, wind speed, and cold air circulation rate affect the freezing speed.

　　3. The influence of latent heat and enthalpy difference: 1kg of water needs 80kcal cooling to drop from 80 degrees to 0 degrees, and 80kcal cooling is also required to change from 0 degrees water to 0 degrees ice. It can be seen that the latent heat of crystallization requires more cooling. Similarly, when the enthalpy difference is large, such as the high temperature of the purchase, not only a large cooling capacity is required, but also a long freezing time is required.

　　4. The influence of food ingredients: Foods with high thermal conductivity coefficient freeze faster than foods with low thermal conductivity coefficient. If the plastic film on the food surface not only conducts heat slowly, but also hinders the wind. For example, the thermal conductivity of water is 0.604w/mk, the thermal conductivity of fat is 0.15, the thermal conductivity of plastic film is 0.028, and the thermal conductivity of wind is 0.066.

　　 5. The influence of food thickness: the square of the food thickness is proportional to the freezing time. The thicker the food, the longer the quick-freezing time.