In the food industry and daily consumption, “quick-freezing” and “-18 ℃ storage” are high-frequency concepts that are often confused. They belong to different parts of the food industry chain, and the essential difference is significant: quick-freezing is the core processing technology, and -18℃ storage is the temperature control standard for circulation and storage.
This article analyzes the differences and connections between the two, for industry practitioners, distributors and consumers to provide reference to help clarify the logic of quality control of frozen food.
What is Quick Freezing Technology
Core Definition and Technology
Quick-freezing technology is a highly efficient low-temperature processing technology in the field of food processing, the core of which is to reduce the center temperature of food to below -18℃ in a very short period of time with the help of special equipment and standardized processes.
Unlike ordinary freezing, the key advantage of quick-freezing is to inhibit the overgrowth of ice crystals inside the food through rapid cooling, forming tiny and uniform ice crystals, thus preserving the original nutrients, flavor substances and physical texture of the food to the maximum extent, and reducing the damage to the cellular structure.
Core Equipment and Standardized Process
Equipment
The quick-freezing process needs to rely on special refrigeration equipment to achieve, the mainstream types include blast-type quick-freezer, liquid nitrogen quick-freezer, plate-type quick-freezer and so on. Among them, liquid nitrogen quick-freezer is widely used in the processing of fresh ingredients with extremely high quality requirements due to the advantages of fast cooling speed and even distribution of low temperature, which can minimize the quality loss of ingredients.
Standardized Process
- Pre-treatment: Fresh raw materials are rinsed with water, ultrasonically cleaned to remove impurities, pesticide residues and microorganisms, and then cut into forms suitable for freezing according to the characteristics of the ingredients, and some of the ingredients need to be flavored, blanched or drained. The whole process of low-temperature aseptic operation, strict control of time, optimize the subsequent freezing effect, to avoid the loss of nutrients and the risk of deterioration caused by exposure to room temperature.
- Fast freezing: the pre-treated ingredients are evenly spread on the material tray (to avoid stacking too thick to affect the uniformity of cooling), and sent to the special quick-freezing equipment. According to the set parameters of the ingredients, the temperature will be lowered rapidly within 30 minutes to ensure that the center temperature passes through the ice crystal generating zone of -1℃~-5℃, and then steadily lowered to below -18℃ to reduce the cell breakage by tiny and uniform ice crystals, and lock the original quality of the ingredients.
- Sealed Packaging: Immediately after freezing into the low-temperature packaging area, the use of composite film and other barrier materials sealed, high-end ingredients can be matched with vacuum, nitrogen filling packaging technology. Exhaust the air inside the bag to prevent oxidative browning, freezer burn and secondary pollution, clearly marked with product information, locking the quality and flavor after freezing.
- Transfer to storage: Packaged qualified ingredients need to be transferred to low temperature cold storage within 10 minutes to avoid room temperature stay to temperature rise. The cold storage is preset and stabilized at below -18℃, the ingredients are placed according to the categories and reserved ventilation gaps, connecting with the subsequent cold chain equipment, maintaining the low temperature chain without interruption to guarantee the quick-freezing effect.
The whole process requires precise control of time and temperature parameters to avoid microbial growth, nutrient loss and oxidative deterioration caused by placing raw materials at room temperature before freezing, and to guarantee the quick-freezing effect.
Main Application Scenarios
The quick-freezing technology is suitable for all kinds of food products that need to be preserved for a long time and require high quality stability, and it has become an important support for the modern food industry. The core application scenarios can be divided into three major categories:
Prefabricated Food
mainly covers quick-frozen dumplings, buns, dumplings, and other rice and noodle products, which are easy to be stored for their flavors and tastes of the fillings and crusts.
The quick-freezing process can quickly lock the fresh flavor of the filling and the soft texture of the crust, avoiding the loss of flavor and dryness of the crust caused by room temperature or ordinary freezing, and meeting consumer demand for the quality of ready-to-eat food.
Fresh Ingredients
include frozen meat, frozen seafood, frozen vegetables and other natural ingredients, whose core demand is to extend the freshness period while retaining the original flavor and nutrition.
Quick-freezing can inhibit the oxidation of internal nutrients and reduce cell breakage, which can better maintain the fresh texture and flavor of fresh ingredients than ordinary freezing, and solve the problem of seasonal and regional supply of ingredients.
Conditioned Food
such as frozen hamburger embryo, fried chicken nuggets, pizza, etc., mainly serves the catering industry. These foods have a strong demand for standardization and efficient supply, and quick-freezing can not only ensure the consistency of quality after mass production, but also provide a convenient storage and processing basis for the catering side, taking into account the efficiency of meals and flavor stability, which is an important support for the development of catering standardization.
Understanding What is -18℃ Storage
-18℃ storage is not a processing technology, but a mandatory temperature control requirement for the whole process of food circulation, warehousing and sales, which means that the ambient temperature should be maintained at a temperature not higher than -18℃ in the links of food transportation, cold storage, and frozen display in supermarkets.
Its core role is to maintain the existing quality of food, inhibit all kinds of quality deterioration factors, to protect the safety of food and extend the shelf life, rather than change the inherent quality attributes of the food itself.
Technical Principle
The core value of -18℃ storage originates from the triple precision control of low temperature on microorganisms, enzyme activity and ice crystal morphology, the specific effects are as follows:
Microorganism Inhibition
Most bacteria, molds and other harmful microorganisms can’t reproduce below -18℃, and the metabolism activities of even low-temperature-resistant cold-loving bacteria will be completely stagnant. This can prevent food spoilage caused by microorganisms from the root cause, providing a core guarantee for food safety.
Enzyme Activity Inhibition
Lipase and protease naturally contained in food will accelerate fat oxidation, protein decomposition and other deterioration reactions. The low temperature of -18℃ can significantly reduce the activity of such enzymes, slow down the deterioration process, and effectively extend the shelf life of food.
Ice Crystal Stabilization
Under the environment of -18℃, the ice crystal form inside the food can remain stable. If the temperature fluctuates above -12℃ (e.g. supermarket freezers are frequently switched on and off, resulting in warming), the ice crystals are prone to recrystallization and enlargement, which will damage the cell structure of the food and affect the final taste and quality.
Limitations Not to be Ignored
It should be clear that -18℃ storage can only “passively maintain” the quality, there are two core limitations, can not fundamentally improve or repair the quality of food:
- Can not repair the existing quality damage: If the food has not been quick-frozen treatment, only ordinary freezing, the internal formation of coarse ice crystals, even in the -18 ℃ environment, will slowly destroy the food cell structure, long-term storage will still appear after the taste of firewood, juice loss and other quality problems.
- Temperature fluctuations are easy to cause quality deterioration: If the storage process of frequent temperature fluctuations (such as supermarket freezers frequently switch to cause the temperature rose to -10 ℃ or so), will lead to obvious recrystallization phenomenon, ice crystals gradually increase, and ultimately destroy the food texture, resulting in flavor loss, weakening the stability of quality.
Key Differences between Quick Freezing and -18 ℃ Storage
The difference between the two runs through the nature, objectives, technical requirements and other dimensions, specifically from the six core dimensions of the clear distinction:
Nature
quick-freezing is the core processing technology of the food production end, through the special equipment and precise temperature control to actively intervene in the freezing process, inhibit the formation of coarse ice crystals, reduce cellular damage, maximize retention of the original quality of the ingredients to achieve the “active optimization”. “Active optimization”, laying the foundation for long-term storage;
and -18℃ storage is the temperature control standard covering the whole chain of circulation and storage, only relying on constant low temperature to inhibit microbial and enzymatic activity and slow down the deterioration, which is “passive maintenance” of existing quality, and can not improve or repair the quality of food. Temperature Requirements
Temperature Requirements
The core requirement of quick-freezing is “rapid cooling and precise temperature control”, which needs a short period of time to let the food quickly cross the ice crystal generating zone of -1℃~-5℃ to avoid the production of coarse ice crystals, and finally reduce the center temperature to below -18℃ steadily;
-18 ℃ storage is required to “long-term constant, eliminate fluctuations”, the whole circulation to maintain the temperature ≤ -18 ℃, to prevent over -12 ℃ fluctuations triggered by recrystallization, temperature stability is the core of control.
Quality Impact
quick-freezing on food quality is “active optimization” effect, through the optimization of ice crystal morphology to reduce the rate of cell breakage, reduce juice and flavor loss, inhibit microbial reproduction in the early stages, from the source to enhance quality stability;
-18 ℃ storage can only be “passive stabilization “, can not repair the existing quality damage, only rely on low temperature to slow down the deterioration, the source of poor quality is the final taste, nutrition is still affected.
Equipment Needs
quick-freezing needs blast type, liquid nitrogen type and other specialized equipment, both cooling fast, accurate temperature control, temperature uniformity advantages, liquid nitrogen quick-freezing machine suitable for high-quality fresh food, the overall technical threshold and investment costs are high;
-18℃ storage rely on low-temperature cold storage, refrigerated trucks, freezers and other insulation refrigeration equipment, the core is to maintain low temperature rather than rapid cooling, focusing on thermal insulation and temperature control and stability, the cost and technology threshold is lower, suitable for the circulation side of the bulk storage and transportation needs.
Time Requirements
Quick freezing needs to be strictly within 30 minutes to complete the freezing operation, the core purpose is to quickly through the ice crystal generation zone, to prevent excessive increase in ice crystals damage to the food cell structure, loss of flavor and nutrients, and freezing needs to be immediately connected to the sealing and packaging, low-temperature transit and other subsequent links, the whole process to avoid the temperature rebound caused by the exposure to ambient temperatures, to protect the effect of quick-freezing.
Storage at -18℃ covers the whole circulation cycle of food from the production end after freezing to the end consumers’ purchase, including cold storage, cold chain transportation, supermarket frozen display and other links, which need to maintain constant low temperature for a long time to eliminate frequent temperature fluctuations and ensure stable quality.
Connection between -18℃ Storage Labeling and Quick Freezing Process
Core Cognition
The labeling of “stored at -18℃” on the food package is the temperature control requirement put forward by the producer for the circulation link, with the purpose of ensuring that the quality and safety of the food will remain stable before it reaches the hands of the consumers.
However, this labeling does not mean that “the food has undergone the quick-freezing process”. In short, “stored at -18℃” is the “preservation condition” of the food, not the “proof of processing technology”, and the two cannot be equated.
Legal Basis of Labeling
The labeling comes from the national standard GB 7718 “National Standard for Food Safety General Principles for the Labeling of Prepackaged Foods”, which requires prepackaged foods to be clearly labeled with storage conditions.
The label “-18 ℃ storage” only indicates that: if the food is stored at a temperature higher than the temperature of the environment, may be due to microbial reproduction, enzyme activity recovery or ice crystals weight crystallization, resulting in a shorter shelf life, quality deterioration or even deterioration, but the standard does not mandate such food must be processed through the quick-freezing process.
Necessity of Labeling Quick-Frozen Foods with “-18℃ Storage”
For food products that have undergone quick-freezing treatment, labeling “-18℃ storage” is a key addition to safeguard the quick-freezing effect, and the core reasons and synergistic relationship between the two can be divided into two aspects:
- Preventing the failure of the quick-freezing effect: quick-freezing only optimizes the initial ice crystal morphology, but does not guarantee the stability of the crystals in subsequent storage. If the storage temperature is higher than -18 ℃, the ice crystals inside the food are easy to recrystallize and increase in size, destroying the cellular structure, directly leading to the loss of the quality advantages formed in the previous quick-freezing, so that the effect of quick-freezing is completely ineffective.
- slow down the chemical deterioration reaction: quick-freezing can not completely block the chemical changes in long-term storage, such as fat oxidation, flavor material volatilization. The constant low temperature of -18℃ can minimize the rate of such reactions, slow down the deterioration of quality, and ensure that the high quality of the frozen state in the whole shelf-life of continued stability.
Complementary Relationship between the Two
quick-freezing and -18 ℃ storage is not an isolated existence, but the formation of “the foundation of the early, the later escort” synergistic closed loop. Quick-freezing as the production end of the process, through the optimization of the ice crystal form for food quality foundation;
-18 ℃ storage as the circulation end of the guarantee, through the constant low temperature to maintain the quality of this advantage, the two work together, in order to provide consumers with safe, excellent taste of frozen food.
How to Determine whether the Food is Quick Frozen Process?
Ordinary consumers can judge in three simple ways:
- First, check the name of the product: labeled “quick-frozen XX” (such as frozen dumplings, frozen shrimp) of the product, clearly after the quick-frozen process; if only labeled “frozen XX”, the probability of ordinary frozen products, did not go through the rapid freezing process.
- 2 is to check the package description: some high-end products will be in the ingredient list or process description column, clearly marked “liquid nitrogen quick-freezing” “fast freezing” and other words, according to which can be directly confirmed that the product using the freezing process.
- Third, observe the quality of the thawed: quick-frozen food thawing juice loss is less, the texture is firm, the taste is closer to the fresh ingredients themselves; ordinary frozen food thawing juice precipitation is more, the texture of the loose, the taste is also relatively inferior.
Common Misconceptions Clarification
Misconception 1: -18 ℃ storage of food are frozen, quality is guaranteed
Truth: -18 ℃ can only guarantee the safety and shelf life of food, can not decide the core quality of food. Ordinary frozen food, even if stored at -18 ℃, because the initial ice crystals coarse, long-term storage of taste, nutrition will still be gradually lost, the quality is far less than frozen food. The core of quality depends on the production process, rather than simply the storage temperature.
Myth 2: frozen food can be stored at 0 ℃ ~ 4 ℃ for a few days, anyway, has been frozen
Truth: frozen food out of the -18 ℃ storage environment, ice crystals melt quickly, microorganisms will be in the 0 ℃ ~ 4 ℃ of the refrigerated environment of rapid reproduction, there are potential safety hazards; if the freezing again, it will lead to serious recrystallization phenomenon, ice crystals increase dramatically.
The complete destruction of the food cellular structure, resulting in texture, nutrients, serious loss of quality can not be recovered. The loss of taste and nutrition is serious, and the quality can not be restored. Therefore, frozen food should be maintained throughout the -18 ℃ storage, open as soon as possible after consumption.
Myth 3: frozen will destroy food nutrition, not as good as fresh food
Truth: frozen technology can lock the nutrition in a short period of time, the test, frozen food can retain more than 90% of the vitamins, minerals and other nutrients; and fresh ingredients from the picking, transportation to the sale, often takes days, during which oxidation, microbial metabolism loss of about 20% of the nutrients, part of long-distance transportation of “fresh” vegetables. Some of the long-distance transportation of “fresh” vegetables, the nutritional content is even lower than frozen vegetables. In addition, quick-freezing can quickly inhibit microbial reproduction, safety is easier to guarantee.
Conclusion
Quick-freezing and -18℃ storage are clearly positioned in the food industry chain, complementary functions of the technical means, respectively bear the “optimization of quality” and “maintenance of quality” responsibilities.
Packaging “stored at -18 ℃” is only the circulation temperature requirements, can not be used as the basis for quick-freezing, need to be integrated product name, packaging instructions and thawing quality judgment. Practitioners and consumers to clarify the difference and correlation between the two, can accurately control the quality, to avoid cognitive misunderstanding.
