[Chinese Packaging Network News] 1. Almost all canned foods can be packaged using metal cans;
The canned metal cans are the common brands in American supermarkets. The foods contained inside are: beans, chicken noodles, mixed fruits, corned beef, sardines, pineapple slices, luncheon meat, and what the ghosts are curried with. sauce. It should not be further explained that the above products already contain vegetables, fruits, meat, noodles, and sauces.
However, considering the inability to use metals, the greatest possibility is that foods with lower pH values ​​are highly corrosive to metals and cannot be used. After checking the FDA website, it was found that most canned foods have a pH of 3.0 or higher, but there is an antithesis. "Vinegar" was as low as 2.0, but I didn't want to understand that vinegar could be used to make cans. There may be some vinegar and peanuts.
As regards the dietitian's reply, "Canned fruits and vegetables are canned in acid, which can easily cause corrosion of metals." There are also general food additives that can be added to canned fruit, such as citric acid, metatartaric acid, benzoic acid and its sodium salt. Accelerate the corrosion of metal cans.†These two views have no problem in itself, but since metal cans have a wide range of applications in fruit-based high-acid foods (pH<4.6), the corrosion of metal cans should have been well resolved. .
Citing Wikipedia's Tin_can page, today's tinned metal cans are tin plated. The tin plated layer is highly resistant to corrosion. The steel also guarantees the mechanical strength of the package. Although metallic tin is highly corrosive, it is still at risk of being corroded by high-acid foods. It has been reported that some people have symptoms of nausea and vomiting after taking canned foods containing 200 mg/kg of tin. However, a 2002 study showed that 99.5% of the tin content of foods in 1,200 cans tested was lower than the UK national standard limit of 200 mg/kg. Compared with previous studies, the results of this test are much higher than before. The big improvement, the researchers concluded that: The manufacturer's practice of painting the inner surface of metal cans greatly improves the corrosion resistance of metal cans, making metal cans safer for use in high-acid foods.
As for beverage packaging such as Coke cans, it is cheaper aluminum skin. Aluminum also has high corrosion resistance. Although the strength of aluminum is poor, the carbonated beverage used to hold internal high pressure is just right.
We have not noticed that the metal skin of the Coke cans is much thinner than the cans. It is precisely because the internal high pressure of the Coke can make the entire metal can bulge like a balloon. It uses the tensile force of the metal skin to resist the impact of the outside world in all directions. Stress, so the wall does not need to be as thick as a can. The inside of the cans is under negative pressure. In order to extend the quality of the food, the hot food is filled before the sealing to remove the air in the can as much as possible, and then seal it again. Negative pressure in cans has two advantages. The first is to reduce the oxygen content in the tank to reduce the oxidation of the food; the second is to invade the lid of the can. Once the internal food is spoiled by the anaerobic bacteria to produce gas, the lid of the can will be Drums come out to remind consumers not to eat.
2. Glass cans are heavy, fragile, and costly.
To give a simple example, a 500ml metal can weighs about 20 to 40g, while a 500ml glass can weighs 200 to 350g. Therefore, glass packaged products cost more to transport than metal packages. Therefore, in countries with large canned foods such as the United States, canned foods on the market are mostly metal canned. Canned foods are everyday consumer goods for ordinary people, and people's acceptance of such foods is also high.
3. Because of its transparent properties, glass cans have a better display effect on the food itself and can improve the product sales.
In China, there are only a few well-known types of canned foods (bean fish, canned fruit, luncheon meat, etc...). Canned foods are less accepted by the general public, and canned fruits are only entered at the beginning of reform and opening up. In the Chinese market, glass packaging has effectively displayed its bright colors and attracted enough audiences.
However, the market share has not been large, if a manufacturer suddenly opened his mind and said we want to save costs and use metal cans, it is estimated that even more no one bought.
China is actually a canned metal canned fruit! Not seen in the country, but often seen in the Chinese supermarkets in Chicago, all kinds of fruit and condensed milk seasoning or something. The reason that is not common in supermarkets may be because the main target customers are restaurants rather than everyday people. Whatever the restaurant uses to make desserts or smoothies, it does not matter whether it is packaged or not. However, the canned metal cans are the memories of childhood.
So glass jars are expensive, and only good-looking foods use glass packaging when they need to attract customers. The canned foods such as meat, chicken noodle soup, and spaghetti are themselves sold after a long period of high temperature treatment. The use of relatively inexpensive and ugly metal cans is just the right choice!
There is the reusability of glass cans, metal cans can not be re-covered after opening, although you can use plastic wrap, but far less convenient for glass cans.
However, it must be pointed out that not all foods are eligible for such re-use treatment. For details, see the section on high-acid, low-acid foods below.
Low-acid canned foods are almost all ready-to-eat and cannot be stored for a long time, even if they are refrigerators. The reason is very simple. The fried dishes at home are not fresh in the refrigerator for 2 days, and they are prone to deterioration after a long time. And high-acid foods such as pickled cucumbers, pickled cabbages, and ketchup, etc., can be stored in the refrigerator for a longer period of time because of the protection of acid (and sometimes salt). Acid and salt are the most natural and oldest food preservatives.
4. Professional science: Why distinguish between low-acid foods and high-acid foods in the food industry?
Low-acid foods, ie foods with a pH > 4.6, such as most canned vegetables. Correspondingly, high-acid foods are foods with pH < 4.6.
High-acid foods are relatively easy to preserve because the high-acid environment can effectively inhibit the growth of microorganisms, especially A, B-type shuttle botulinum.
Low-acid foods, however, Face the risk of botulism. Why is botox so horrible? Because the toxin produced by Clostridium botulinum has very high toxicity (approximately 0.004/kg for humans), it is also an anaerobic bacterium. At the same time, the botulinum spore (wall thickness, low water activity, like the general presence of plant seeds) ) There is also a high degree of heat resistance. Once Botox appears in low-acid canned foods, it will lead to large-scale food safety accidents.
Therefore, the degree of heat treatment required for high-acid foods and low-acid foods is different. Low-acid foods require the use of high-temperature and high-pressure equipment to increase the heat treatment temperature (typically 121°C, 2 times atmospheric pressure). At such high temperatures, it takes 30 to 80 minutes of heat treatment to reach the target to ensure food safety. The high-acid foods only need to be boiled in a water bath (or brine) at normal pressure for a certain period of time (10-40 minutes).
5. Professional Science: Shelf-stable Food.
Last but not least, in fact, foods such as canned food are broadly referred to as “shelf-stable food.†This literally means “shelf-quality foodâ€, that is, it can be stored at room temperature for a long time (more than one year). food.
It must be said clearly that "shelf-stable food" does not include biscuits, instant noodles, dried foods such as dried meat that can be preserved with low moisture content, and honey preserved fruit that uses high sugars and low water activities for preservation. This kind of food often fails immediately after opening the packaging halo, and the packaging can be stored as an emergency reserve.
Due to advances in materials science and food science, the packaging of such foods is not limited to metal and glass. Plastic packaging has become more and more common. The advantage of plastic packaging is that it can be directly heated in a microwave oven, which is more convenient and convenient than instant noodles. At noon before the lab often lazy to go out to eat to buy food from the vending machine, eaten pasta, chicken and mashed potatoes, but the taste is ... ... mainly for thorough sterilization, most of these foods after high temperature for a long time Heating, color and flavor are ruthlessly smashed. How to make these foods more delicious and healthy is the direction of our food engineering efforts.