Estimated reading time: 7 minutes
- For consistency, this article focusses on beef sirloin, which is a boneless cut.
- Stress before slaughter can significantly impact meat quality.
- The species of origin significantly affects shelf life.
- Cooked meat generally has a longer shelf life than raw meat, and the packaging method also plays a significant role.
- Bacteria can severely affect shelf life and, in some cases, pose life-threatening risks.
When meat shelf-life guidelines are followed diligently, they guarantee a safe and enjoyable eating experience. Ignoring them, however, can result in an unexpected trip to the hospital.
In the January issue of Stockfarm, Dr Gerhard Neethling, manager of the Red Meat Abattoir Association (RMAA), shed light on abattoir practices that influence how long meat stays fresh. In this follow-up, Prof Arno Hugo, a food scientist in the Department of Animal Science at the University of the Free State, explores how long meat can actually last once it reaches stores.
For consistency, this article focusses on beef sirloin, which is a boneless cut. The question is simple yet critical: If a piece of sirloin was left at room temperature on a kitchen counter, without refrigeration or packaging, how long would it remain safe to eat?
Temperature and pH
According to Prof Hugo, unpackaged meat begins to show signs of spoilage, such as sliminess, within a day. Even vacuum packaging does little to prevent this if conditions are unfavourable, although temperature plays a significant role in slowing spoilage.
When the meat is placed in a polystyrene tray, wrapped in cling film, and stored in a refrigerated display counter at a butcher’s or supermarket, it may start to discolour after three to five days, but this does not necessarily indicate spoilage. Vacuum-packed meat, refrigerated immediately after processing, can be matured for up to around 30 days at 2°C.
A common method of maturing meat involves storing the hindquarters of beef cattle in a cold room for approximately ten days. A more modern approach is dry aging, in which whole cuts, such as sirloin, are matured for longer periods under controlled conditions.
The pH of meat is a critical factor because microbes grow best at a neutral pH of 7. Top-quality beef sirloin, for example, typically has a pH between 5,3 and 5,7 around 24 hours after slaughter. “The higher the pH, the faster spoilage organisms multiply,” explains Prof Hugo. “The slaughter process is therefore crucial, as it strongly influences meat pH.”
After slaughter, muscle tissue converts glycogen (the energy source in the muscle) into lactic acid, which lowers the meat’s pH and helps extend shelf life.
Animal welfare pre-slaughter
Stress before slaughter can significantly impact meat quality. When an animal experiences high stress, its muscle glycogen stores are rapidly depleted. Factors that contribute to stress include transport time to the abattoir, handling methods, heat stress, and possibly hunger or thirst. As Prof Hugo explains: “If an animal experiences stress before slaughter, there is insufficient glycogen in the muscles to produce lactic acid, preventing the pH from dropping adequately.”
When the pH is high, the resulting meat is typically very dark, which is known as a dark cutter. This meat also has a reduced shelf life under normal refrigeration and cannot be matured effectively.
Minimising stress is therefore essential to avoid an undesirable meat colour. Best practices include careful handling during transport and at the abattoir, as well as correct stunning procedures during slaughter. Prof Hugo says animal welfare in this context largely pertains to how animals are treated in the hours before slaughter. “Animals are often transported over long distances to abattoirs, which naturally increases stress.” He recommends that animals rest overnight and have access to sufficient clean water. “Some animals travel 18 hours from Namibia to be slaughtered in Cape Town, making these practices crucial.”
Post-slaughter, proper carcass cooling is also important. Even with optimal handling, beef should be sold within five days, as the meat’s colour deteriorates after this period. “The South African consumer prefers meat with a cherry-red colour,” he notes.
Species-specific storage
The species of origin significantly affects shelf life. Cattle and sheep are warm-blooded, while fish are cold-blooded. When beef or mutton is refrigerated, the microbes present experience a sudden temperature shock, which slows their activity and extends shelf life. In contrast, fish are naturally cold before processing, so refrigeration does little to affect microbial survival. The microbes in fish are adapted to cold temperatures, meaning there is minimal cold shock, and refrigerated fish has a much shorter shelf life. These microbes break down fish tissues, making preservation of refrigerated fish more challenging compared to meat from warm-blooded animals.
The chemical composition of meat also influences shelf life, which explains why different species’ meats store differently. Properly handled beef and mutton can be frozen for up to two years; pork and chicken, however, have a significantly shorter frozen shelf life – typically no longer than six months – even under optimal handling conditions, because their fat can become rancid. Frozen fish has an even shorter shelf life of usually no more than a month, because the type of fat it contains can easily turn rancid.
For the same reason, Prof Hugo advises against producing and freezing boerewors in large batches. The salt in boerewors can accelerate rancidity, especially when using pork fat. A better approach is to freeze the meat in smaller portions and defrost it as needed to make fresh boerewors. Once a batch is finished, a new batch can be prepared from fresh meat, ensuring quality is maintained.
Packaging methods
Cooked meat generally has a longer shelf life than raw meat, and the packaging method also plays a significant role. “In principle, a product will always last longer if cooked in its final packaging,” explains Prof Hugo.
For example, polony can last for up to six months because it is cooked inside its final packaging. Vienna sausages, on the other hand, are cooked differently (outside the final packaging), and does not last as long.
Over the years, various methods have been developed to extend meat’s shelf life. Biltong, for instance, has long been one of South Africans’ favourite meat options, and historically, people also preserved meat by pickling it in brine.
Another interesting historical method involved cooking wors, placing them rolled in sterilised glass bottles, pouring hot fat over them, and sealing them airtight. The fat acted as a preservative, preventing the meat from spoiling.
Modern techniques such as vacuum packaging further extend shelf life. Since microbes require oxygen to grow, removing oxygen during vacuum packaging significantly slows down spoilage.
Bacteria and hygiene
Bacteria can severely affect shelf life and, in some cases, pose life-threatening risks. A stark example is the 2017/18 listeriosis outbreak, which claimed 216 lives. In 2024, the National Health Laboratory Service (NHLS) confirmed that the outbreak originated from a processed meat facility of Enterprise Foods, a division of Tiger Brands. The incident made 1 060 people ill.
This tragedy continues to cast a shadow over the country’s food industry, highlighting how microscopic bacteria can have enormous consequences. According to Prof Hugo, safe handling of meat is the most effective way to prevent such outbreaks. “Much is done to maintain meat hygiene in processing facilities. For instance, employees work at controlled temperatures of 10°C and wear gloves and hair coverings at all times.”
In addition, knives are sterilised between operations, and workers wash their hands regularly. “Fact is, the cleaner you handle a product, the fewer microbes contaminate it.” Although microbes are invisible to the naked eye, their presence is inevitable.
Immediately after slaughter and cutting, meat is contaminated with microbes acquired through hand contact, knives, air, and other sources. “Suppose at least 1 000 microbes are present on the meat. After 20 minutes at room temperature without packaging, the number doubles to 2 000, then 4 000, and 8 000. Within two hours, it can reach 32 000.” The higher the microbial load, the faster the meat spoils and the shorter its shelf life becomes.
Life-threatening pathogens
Some organisms can act as disease-causing pathogens. These pathogens may produce toxins or trigger infections that can make people seriously ill, require hospitalisation, or even be fatal.
The rate of spoilage can be slowed by storing sirloin at 4°C, as most microbes cannot grow at this temperature.
However, the meat value chain can do only so much to maintain meat quality. Consumers also have a responsibility to handle meat safely by preparing it in a clean, hygienic environment. So, always wash your hands, work surfaces, and utensils. – Susan Marais, Stockfarm
Send an email to Prof Arno Hugo at hugoa@ufs.ac.za for more information.
