In the 1970s and 1980s, it was such a joy and pride to be able to eat tomato and braised noodles in winter! At that time, many people bought tomatoes home, made tomato paste, and saved them for winter. The way to make tomato sauce at home is very simple, just wash the tomatoes, blanch them and peel them, put them in a salt water bottle, then put a rubber stopper, insert a needle, put it on a steamer and steam for about 30 minutes, then unplug it. Needles, chilled so the tomato paste can be stored until winter, with great flavor and color. The production of canned food is the same as the principle of making tomato sauce at home. The raw materials are processed well, put into cans (tin cans, glass bottles or flexible packaging bags), vacuumed and sealed, and then heated and sterilized. After cooling, the canned product is the finished product. After the food is put into the can, after exhausting, sealing, sterilizing and other processes, the container is completely sealed and is in an oxygen-free environment. The sealed food in this sterile state has no conditions for the growth and reproduction of microorganisms (bacteria) outside the can. No bacteria can get into the tank, so the food will not spoil, and there is no need to add any preservatives at all. Besides, canned food has a history of more than 200 years, and there were no preservatives at all. Canned food is safe, nutritious, convenient and convenient. It is very popular in Europe, America and Japan. China's canned food is exported about 3 million tons every year and sold to more than 100 countries. Most of aerospace and submarine food are canned. In fact, canned food is closely related to our lives. In the catering industry, sweet corn, tuna, mushrooms, ketchup, fruit in yogurt, and decorative fruits for birthday cakes are all canned food. As a raw material, eight-treasure porridge on the market is a typical canned food.