Quick-freezing is a common process in modern food processing, widely applied to products such as fruits, vegetables, meat, and aquatic products. Items such as quick-frozen strawberries, mangoes, peas, corn, french fries, and chicken all rely on this freezing process to extend their shelf life and facilitate transportation.
Compared to conventional freezing, rapid freezing places greater emphasis on freezing speed, ice crystal size, and the final quality of the product. So, what is the purpose of freezing, and exactly what problems does it solve?
1. What is quick-freezing?
Quick-freezing refers to the process of rapidly lowering the temperature of food within a short period, causing the moisture inside to quickly form ice crystals and bringing the product’s core temperature down to a specified freezing level.
In food processing, quick-freezing typically follows preliminary steps such as washing, cutting, blanching, frying, or steaming. For instance, vegetables destined for quick-freezing might undergo washing, cutting, blanching, and cooling before entering the freezing stage, whereas fruits might be frozen directly after washing, peeling, and cutting.
2. What is the primary purpose of quick-freezing?
Extending the shelf life of food
At room temperature, food is susceptible to factors such as microbial proliferation, enzymatic activity, and oxidation; over time, this can lead to spoilage, discoloration, and the development of off-flavors.
Quick-freezing rapidly lowers the product temperature, significantly inhibiting microbial growth and reproduction while slowing down various chemical and biological reactions. Consequently, food can be preserved for a longer period in a frozen state, facilitating inventory management, long-distance transportation, and seasonal supply for businesses.
Preserve the food’s original quality as much as possible
During the freezing process, the water content in food forms ice crystals. If the freezing rate is slow, these crystals tend to grow larger, causing significant damage to the food’s cellular structure. Upon thawing, this can lead to issues such as juice loss, tissue softening, and a decline in texture and mouthfeel.
Rapid freezing minimizes the time the food spends passing through the zone of maximum ice crystal formation; this results in smaller, more uniformly distributed ice crystals, thereby reducing the impact on the product’s structural integrity.
Reducing Moisture Loss
During storage and processing, improper temperature control can lead to moisture migration and product dehydration.
Rapid freezing quickly stabilizes the moisture state within the food and minimizes the formation of large ice crystals, thereby helping to reduce drip loss during thawing.
Preserving Color, Flavor, and Nutritional Value
Many fruits and vegetables are prone to oxidation and enzymatic reactions during processing, leading to browning, darkening, and flavor changes.
In industrial production, some products undergo steps such as blanching and cooling prior to quick-freezing. Blanching reduces the activity of certain enzymes, while subsequent rapid cooling and quick-freezing further lower the product temperature, thereby helping to stabilize product quality.
3. Why do different types of food require quick-freezing?
Although quick-freezing technology can be applied to various foods, the specific objectives and processing requirements differ.
Quick-frozen fruits: The primary focus is on color, shape, cellular structure, and texture after thawing; common products include quick-frozen mangoes, strawberries, and blueberries.
Quick-frozen vegetables: Processing typically involves a combination of blanching, cooling, and quick-freezing, with a focus on controlling color, texture, and microbial levels; common products include quick-frozen peas, corn kernels, carrots, and green beans.
Quick-frozen meat: This is primarily used to extend shelf life while preserving the meat’s tissue structure, color, and quality as much as possible.
4.Common Industrial Quick-Freezing Equipment
In industrial production, quick-freezing is typically carried out using specialized quick-freezing machines rather than simple freezing in standard cold storage units.
Quick-freezing machines rapidly extract heat from food products—using forced cold air or other refrigeration methods—enabling the products to reach the target temperature within a short period.
Common types of industrial quick-freezing equipment include:
- Fluidized bed quick-freezers
- Tunnel quick-freezers
- Spiral quick-freezers