Why do you have to leave the fresh meat aside for a few days instead of eating it?

Review expert: Wang Guoyi, Postdoctoral Fellow in Nutrition and Food Safety, China Agricultural University

When Chinese people eat, most of them like to try something new.

Whenever people go out to buy things, they are undoubtedly keen on buying fresh vegetables. Vegetables that have just been picked from the fields and transported directly to the market are generally considered to be the best vegetables. If they buy aquatic products, they must be fish and shrimps that are alive and kicking in water tanks and "rampant" crabs to be fresh enough. The same is true for meat: many people are obsessed with buying fresh meat, especially pork, beef and mutton that are slaughtered in the early morning and sold immediately in the morning.

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But if you taste it carefully, the opinions are mixed as to whether this kind of meat is the most delicious .

Effect of “post-ripening” on meat quality

In fact, as early as ancient times, people had discovered that freshly slaughtered livestock meat was not the best in taste and flavor.

In contrast, many meats will reach their best taste and flavor after a period of time after slaughter and cutting. For example, pork and beef are better if they are left at the right temperature for a period of time after slaughter, that is, meat that has been "aged" or "post-ripened".

Source: pexels

Most people are still unfamiliar with the concept of "post-ripening", so let's start with the three types of meat that can often be purchased in markets and supermarkets.

First, let’s talk about the “hot fresh meat” that the public is most familiar with, which is the “freshest” meat that everyone has known since ancient times. It is usually slaughtered in the early morning and put on the market early in the morning, and the meat still maintains a certain temperature.

Once slaughtered, livestock will immediately enter the rigor mortis process, which generates a certain amount of heat, causing the meat temperature to rise to about 40°C. This temperature is particularly suitable for the growth and reproduction of microorganisms, especially bacteria such as Salmonella and coliforms. Therefore, if the meat is not thoroughly cooked after slaughter, there is a risk of food poisoning.

In order to solve this food safety problem and optimize the meat transportation and storage process, frozen meat and fresh meat appeared.

We are all familiar with frozen meat , which is meat that is frozen and preserved in an environment of about -18 degrees Celsius.

Chilled meat , also known as chilled meat, cooled and acid-drained meat, and acid-drained refrigerated meat, refers to fresh meat that is quickly cooled after livestock are slaughtered, so that its temperature drops to 0-4°C within 4 hours and is always kept within the range of 0-4°C during subsequent processing, circulation and retail.

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All meat from livestock and poultry that has undergone a pre-cooling and acid-removal process is called fresh meat. The most common ones include fresh pork, fresh beef, fresh mutton, fresh chicken, etc.

Hot fresh meat, frozen meat, and cold fresh meat, these three types of meat have completely different texture and taste because of their different storage and circulation methods.

After livestock and poultry and other animals are slaughtered, their meat will go through three stages: rigor mortis, thawing, and maturation .

The meat is soft right after slaughter, but within a few hours, it will gradually become stiff, which is called rigor mortis, and lasts for 1 to 3 days. During this period, due to the strong muscle contraction, the taste of the meat is the worst. Therefore, the taste of hot fresh meat is not good, the taste is not beautiful, and the meat is relatively hard.

Source: pexels

Freezing hot fresh meat, that is, freezing meat, will cause stronger muscle contraction and a worse taste.

However, if the slaughtered meat is stored at 0-4℃ for a period of time, the meat will gradually become soft again, that is, after the thawing period, it will reach the maturity period. Because the meat maturity process occurs after slaughter, the concept of the ripening period after the grain seeds are picked is borrowed, and this process is called "post-ripening treatment", which is actually what we usually call the "acid removal" process.

The reason why it is called the acid removal process is that after slaughter, the glycogen stored in the meat will be degraded to form lactic acid. At the same time, in this process, the protein in the meat is broken down by proteases to tenderize the muscles and produce a large amount of umami substances.

Source: pexels

After such a "maturation" process, the meat becomes softer, more tender and delicious. Therefore, the acid-removed meat, that is, fresh meat, is more delicious, not only with a good taste but also with a stronger flavor.

In addition, because fresh meat is kept at a low temperature throughout the entire processing, circulation and sales process, the activity of enzymes in the meat and the growth and reproduction of pathogenic microorganisms are inhibited, thereby improving food safety.

What are PSE meat and DFD meat?

Although the names of PSE meat and DFD meat are unfamiliar, many people may have bought or eaten them.

Many factors can induce stress responses in livestock before slaughter, and these two types of meat may be produced after slaughter.

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PSE meat refers to pork, commonly known as water pork . On the one hand, it is because the lean pig breed itself is highly responsive to stress. On the other hand, external stimuli, such as being driven, transported over long distances, stunned, and high temperatures before slaughter, may cause stress reactions in pigs. Then, the muscles after slaughter may be pale, soft and inelastic, and gravy may ooze out of the muscle surface. This kind of pork is commonly known as white muscle, or "boiled" meat, which corresponds to Pale Soft Exudative Meat in English, referred to as PSE meat.

DFD meat, in simple terms, is meat whose muscle pH value after slaughter is above 6.5.

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Similarly, if livestock are in a state of stress for a long time before slaughter, such as poor feeding conditions, long transportation, inappropriate waiting time for slaughter, etc., they will produce a greater stress response, causing the livestock muscle glycogen content to be lower than normal, and the lactic acid produced by glycogenolysis after slaughter will be insufficient. The pH value within 24 hours cannot drop to the normal range (5.4~5.7), but is as high as 6.5 or above. The high muscle pH value will form dark red, hard texture, dry surface meat, that is, DFD meat, which corresponds to the English words Dark, Firm and Dry.

These two types of meat are not only deficient in nutrition, but also cause serious economic losses to related practitioners. Therefore, all links in my country's meat industry chain are constantly being improved to reduce the incidence of these two types of meat.

How to choose and buy meat?

As early as 2002, the "Tenth Five-Year Plan for the Development of the National Food Industry" described my country's meat processing enterprises as follows: "During the 'Tenth Five-Year Plan' period, we will vigorously develop chilled meat, cut meat and various types of cooked meat products for direct consumption, and gradually increase the proportion of cooked meat products in meat consumption."

Chilled meat, that is, fresh cold meat, is vigorously promoted by the country in the hope that it can gradually replace the traditional model of "live storage and fresh sales", keep pace with the international standards more quickly, and it is also an inevitable trend for it to enter people's lives with more scientific and nutritional concepts.

Since the 1950s and 1960s, developed countries have begun to research and promote de-acidified meat, while my country started around the 1980s. In developed countries such as Europe and the United States, the retail of hot fresh meat and frozen meat has basically disappeared, and de-acidified meat accounts for more than 90% of the fresh meat consumed.

But in our country, the consumption of fresh meat is much lower.

Source: pexels

On the one hand, since chilled meat requires a full cold chain, the cold chain system has not yet been fully improved, especially in rural areas and farmers' markets where transportation is relatively underdeveloped, and people can only buy hot fresh meat;

On the other hand, in the public's perception, hot fresh meat is often considered better. In addition, the price of cold fresh meat has increased due to the entire cold chain, which will also cause many consumers to switch to buying hot fresh meat.

In short, if conditions permit, it is recommended that you choose cold fresh meat that is safe, high-quality, hygienic, nutritious and tastes good. For meat ingredients, freshly slaughtered meat is not the most ideal state for consumption.