1. The principle of quick freezing
Freezing is to extract the heat energy the product until the latent heat of ablation of the free water molecules in the product is removed, the water becomes a fresh-keeping method of ice crystal structure. It can effectively inhibit the activity of microorganisms enzymes. Frozen preservation method occupies an important position in the fruit vegetable processing industry.
The water in fruits vegetables is pure water, but a mixed solution containing organic inorganic substances. These substances include salts, sugars, acids more complex organic molecules such as proteins trace gases. Therefore, fruits vegetables have to drop below 0°C to produce ice crystals, the temperature at which the ice crystals begin to appear is the so-called freezing point freezing point. When the liquid temperature drops to the freezing point, the liquid phase the crystalline phase are in equilibrium. To make the liquid become crystalline, it must break through this equilibrium state, that is to say, the temperature of the liquid phase must be lowered to slightly below the freezing point temperature. When the liquid is in a supercooled state, a crystallization center is generated due to a certain stimulus. After a stable crystallization center is formed, if the heat continues to be lost, the ice crystals will increase time to time. The heat released by the phase change during crystallization will cause the water The temperature of the aqueous solution rises the supercooling temperature to the freezing point temperature, the liquid becomes solid, which is called freezing. Ice formation includes two processes, namely the formation of crystal nuclei the increase of crystal nuclei. The crystal nucleus is composed of a small number of water molecules separated into granular particles in an orderly manner. The size of the crystal structure is related to the number of crystal nuclei the freezing speed. Under quick-freezing conditions, crystal nuclei are generally formed inside outside the cells of fruits vegetables, with a large number of crystal nuclei, which are needle-shaped crystals are evenly distributed. This kind of spreading will damage the cells tissues, it is easy to recover after freezing, which better maintains the original quality of fruits vegetables. If fruits vegetables are frozen then frozen, the number of ice crystals will decrease. The increase of ice crystals will damage cell tissues. After freezing, the juice will flow out, the texture will be rotten, the flavor will disappear, which will affect the quality of the product. Therefore, in the process of quick-frozen storage, it is necessary to prevent temperature fluctuations, otherwise, even quick-frozen products will lose the advantages of quick-freezing. The principle of quick-freezing control of corn kernel quick-freezing production line is of positive significance to the commercial quick-freezing preservation of fruits vegetables.
2. Quick freezing process
The principle of quick freezing of fruits is basically the same as that of vegetables. The big difference is that most fruits do need blanching, while most vegetables must be blanched. Taking fruits as an example, the quick-frozen preservation process is:
Raw material picking → selection → washing → peeling → stalk removal → core removal → grading → cooling → sugar vitamin C → quick freezing → weighing → packaging → quick freezing storage → transportation → sales.
3. Operating points
(1) Fruit blanching with sugar instead of hot water Soak the fruit in syrup with without vitamin C instead of hot water blanching to prevent mold growth. Generally speaking, individual quick-frozen fruits do need to be blanched. Some fruits such as peaches apples often brown during the quick-freezing process. Even if they are soaked with sugar, they will still show discoloration after a certain period of storage. In order to avoid this browning of the fruit maintain its original color, the cabinet-type liquid nitrogen quick-freezer should add 0.1% to 0.5% vitamin C in the sugar solution.
(2) Fruits must be quickly frozen after cooling draining. The commonly used cold air temperature is -30℃~-40℃, the wind speed is 2m/s~17m/s. When freezing, the cold air is forced to blow the bottom to the top of the mesh belt at a sufficient speed. The fierce air current blows suspends the product, just like a boiling fluid. The low-temperature cold air can directly contact the product particles, resulting in great heat exchange. The ground is enhanced the freezing speed is accelerated. For fruits, liquid sheet freezers are generally used. Because this kind of freezers has the hidden danger of damaging fruits, the commonly used granular freezers-mesh belt freezers. During the freezing process, ensure that the fruits do show uneven accumulation.
(3) Adhere to the low temperature state in the circulation link The entire circulation link should be stopped under freezing conditions below -18°C.
4. Food freezing
Frozen food should be stopped resumed before use. Freezing freezing are two opposite heat transfer processes. The freezing of non-fluid food is slower than freezing. Frozen food should be frozen on the way of eating, should be stored for a long time after freezing. Food, the faster the freezing process, the better. Freezing can be stopped in the refrigerator, at room temperature, cold warm water, can also be frozen by microwave. Microwave freezing is average fast. The price of a small quick-freezer, but the organization composition of the processed fruit vegetable products must be evenly different in order to obtain a good freezing effect.
Name: Shaoxing Donglong Refrigeration Air Conditioning Co., Ltd.
Address: Dongshan Road, Economic Development Zone, Shangyu District, Shaoxing City, Zhejiang Province
Switchboard: 0575-82189677 82605100