Strawberry quick-freezing preservation is to put the strawberry fruit in -25 ℃ below the low temperature, so that it is rapidly frozen in a short period of time, so as to achieve the purpose of refrigeration preservation. Compared with other methods, better able to maintain the shape of the fruit, freshness, natural color, inherent flavor and nutrients, while the process is simple, clean and hygienic, is currently the longest way to keep strawberry fruit fresh. Domestic and foreign applications are now extremely wide. Quick-frozen strawberries can be supplied to the market at any time fresh sales, but also can be used as raw materials for processing to extend the processing period. In recent years, China's frozen strawberries have been shipped to Japan, Hong Kong and Southeast Asia in some areas.
Principle of quick-freezing freshness: quick-freezing strawberry fruit in the majority of water to form ice crystals, due to the rapid freezing, the water inside the cell can not diffuse in time to form small ice crystals, in the cell and the cellular gap in the uniform distribution of the cells from the mechanical damage caused by deformation or damage to the cells, so as to maintain cell integrity in its original state; strawberry juice to form ice crystals, contaminated with bacteria and molds on the berry, microorganisms, due to the lack of water for survival. Microorganisms, due to the lack of water for survival, life activities are inhibited; low temperature hinders the activity of enzymes within the berry, so that it can not or hardly play a catalytic role. Thus, the strawberry fruit can be kept fresh for a long time.
The quality of different varieties of quick-frozen freshness is different, some varieties of quick-frozen quality is excellent, suitable for quick-frozen freshness of the varieties of Dana, spring, Baojiao early birth, stone berry one, etc.; some varieties of quick-frozen quality after the deterioration of the quality of, such as the ball, four seasons, etc. is not suitable for quick-frozen.
The strawberry fruit used for quick-freezing freshness should have: ① Requirements for fruit ripeness is consistent, to the fruit surface coloring more than 80%, the color and flavor has been fully embodied the characteristics of the varieties as appropriate. Only suitable maturity after quick-freezing to keep everything intact, no odor. ② fruit size neat, quick-frozen fruit to choose the size of uniform fruit, single-fruit weight of 7 to 12 grams, horizontal diameter of not less than 2 cm of fruit. ③ fruit fresh, intact, used for quick-freezing fresh fruit must ensure freshness, generally picking the day of processing, such as the day of processing is not complete, should be placed in 0 ~ 5 ℃ cold storage for a short period of time to save; should be selected fruit intact, color and lustre of the fruits of the bright, for a number of pests and insects, deformed fruits, moldy fruits, over-ripe fruits and so on should be eliminated to ensure that the quality of the raw material.
The production process of quick-frozen freshness: acceptance → washing → disinfection → washing → calyx → pick → washing → water control → weighing → sugar → plate → quick-frozen → bagging → sealing → packing → freezing.
The main operation technical points: ① acceptance. The main variety should be pure, fruit size and maturity to meet the standard; ② wash the fruit. Put the fruit in a pool with a water outlet, with running water to wash the fruit, remove impurities, clean the raw materials. ③ Sterilization. Available 0.05% permanganate solution for 4 to 5 minutes, and then rinse with water. ④Water control. After the last water shower, the strawberry filter control for about 10 minutes, control the excess water outside the fruit, so as to avoid the surface of the frozen products with water adhesion. If the frozen products are in granular shape, the water control time should be longer; if the frozen products are in block shape, the water control time can be shorter. ⑤ Add sugar. Add sugar according to 20% to 25% of the weight of strawberries, and add sugar according to 25% of the varieties with heavy sour flavor, and then mix well; the frozen products as processed raw materials do not need to add sugar. (6) Plating. Requirements for frozen products in the form of blocks must be placed flat, tight; requirements for frozen products in the form of particles, placed loosely, so as not to block not easy to separate. (7) quick-freezing. Set up the plate, immediately sent to the temperature of -25 ℃ below the quick-freezing room for quick-freezing, in order to quickly freeze to ensure the quality of quick-frozen strawberries, strawberry plate in the quick-freezing room to be placed in a single layer, generally by 4 to 5 hours to achieve the freezing requirements, and then can be quick-frozen strawberries after the fruit even after the plate to get to the 0 ~ 5 ℃ of the cooling room according to the requirements of the packaging, packing, and then immediately into the temperature of -18 ℃, humidity is 100%! The cold room for storage. This method can be stored for 18 months, fresh sales at any time, and can maintain the inherent flavor of strawberries.
Frozen strawberries must be thawed before eating, not thawed frozen strawberries to eat only frozen feeling, taste the sweet flavor. The thawing method is to put the frozen strawberries into the container, and then put the container into the warm water, thawed and eaten immediately, can not be thawed and then re-frozen or thawed and placed for too long.