Freezing is one of the most effective methods of significantly extending the shelf life of food while helping to preserve its quality. Although many consumers believe that frozen food is completely protected from all potential hazards, freezing merely slows the growth of microorganisms; it does not destroy them. Therefore, improper freezing and particularly improper thawing can significantly increase the risk of foodborne illness. The World Health Organization (WHO), the Codex Alimentarius Commission, the United States Department of Agriculture (USDA), and the European Food Safety Authority (EFSA) consistently emphasize that the safety of frozen food depends not only on its initial quality but also on how it is stored and handled by the consumer.
During the freezing process, the temperature of the food drops to a level at which the water required for microbial growth turns into ice crystals. Under these conditions, bacteria virtually cease to multiply, although many of them remain viable. This means that Salmonella, Listeria, Campylobacter, and other pathogenic bacteria may still be present in food after it has been frozen. Freezing must therefore not be regarded as a method of disinfecting or sterilizing food.
Safe freezing begins with the proper preparation of food. Fresh meat, fish, poultry, convenience foods, prepared meals, and other perishable products should be placed in the freezer as quickly as possible so that they do not remain for an extended period within the so-called “temperature danger zone,” which ranges from approximately 5°C to 60°C. Bacteria multiply particularly rapidly within this temperature range. Therefore, if food is left at room temperature for several hours, freezing it will not neutralize the microorganisms that have already multiplied during that time.
According to international recommendations, freezer temperatures should be maintained at -18°C or below. Under these conditions, food retains both its safety and its sensory properties for a considerably longer period. Nevertheless, freezing does not stop every chemical and physical change. Over time, a food’s colour, texture, flavour, and moisture content may change, which is why the recommended storage periods for different foods should be observed.
Consumers often wonder how long frozen food can be stored. According to the USDA, food that has been properly frozen can remain safe in the freezer for an extended period, although its quality will gradually deteriorate. For example, raw beef retains its best quality for approximately two to four months, a whole chicken for up to about one year, while the recommended storage period for fish depends on the species and fat content. It is therefore advisable to label every frozen product with the date of freezing so that its storage period can be easily monitored.
Thawing is the stage at which mistakes occur most frequently. Many people leave food on the kitchen counter for several hours to allow it to thaw quickly. This practice is not recommended because the surface of the food may reach a temperature at which bacteria multiply rapidly while the centre remains frozen. Such conditions are particularly favourable for microorganisms such as Salmonella spp., Escherichia coli, and Staphylococcus aureus.
The most highly recommended method of safe thawing is to place the food in a refrigerator maintained below 5°C. Although thawing takes place slowly under these conditions, the risk of bacterial growth is minimized. Large items, such as a whole chicken or a large cut of meat, may require more than 24 hours to thaw completely, so preparation should be planned in advance.
When food must be thawed quickly, placing it in leak-proof packaging under cold running water is considered a safe alternative. The water must be genuinely cold rather than warm, as warm water increases the risk of bacterial growth. Another safe method is thawing food in a microwave oven. In this case, however, the food must be cooked immediately, as microwave thawing may partially warm certain areas and create favourable conditions for bacterial growth.
A frequently asked question is whether food can be refrozen after it has been thawed. According to recommendations from the USDA and the Codex Alimentarius Commission, food may be safely refrozen if it was thawed in the refrigerator at a safe temperature and remained at or below 5°C throughout the process. However, each cycle of freezing and thawing reduces the quality of the food because ice crystals damage its cellular structure, resulting in moisture loss and changes in texture. Food thawed at room temperature must not be refrozen.
Preventing cross-contamination is also essential when handling frozen foods. Raw meat, poultry, and fish should be stored separately and on different shelves. A separate container should be used during thawing. After handling these products, hands should be washed and utensils including knives and cutting boards-as well as work surfaces should be cleaned thoroughly.
Although freezing is an effective preservation method, it is not a substitute for proper cooking. Foods of animal origin, in particular, must be cooked to a temperature sufficient to destroy pathogenic microorganisms.
Safe freezing and thawing are not merely matters of food storage; they are everyday practices that directly affect human health. Following a few simple rules such as freezing food promptly, storing it at -18°C, thawing it safely in the refrigerator, preventing cross-contamination, and cooking it thoroughly significantly reduces the risk of foodborne illness. An informed consumer is the most important link in the food safety chain.
