Retort bags are generally made of soft aluminum foil with a thickness of 9 μm, which has excellent moisture resistance, gas resistance and light resistance. If there is no mechanical damage and pinholes, it is completely impermeable to moisture, air, and light. , and has extremely high heat resistance and oil resistance, so the composite packaging bag containing aluminum foil has the properties of full sealing, high fragrance retention, high oil resistance, and high temperature resistance. When choosing the aluminum foil used in the cooking bag, there are three points to pay attention to: 1. The surface cleanliness of the aluminum foil should be high, there should be no oil stains and dust, and the surface tension should be high, which should reach more than 72mN/m. A simple method is to test with distilled water, which should be fully wetted on the surface of the aluminum foil. If the surface of the aluminum foil is seriously oily, it will affect the composite fastness of the aluminum foil and other materials, especially after the packaging bag is cooked at high temperature, delamination and peeling will occur. 2. The number of pinholes in the aluminum foil should be less. Aluminum foil should be the material with the best barrier properties, but if it has pinholes, its barrier properties will be greatly reduced, gas and light will penetrate quickly and directly, and the contents will soon deteriorate. Generally speaking, the thicker the aluminum foil, the fewer the number of pinholes. For example, the number of pinholes in the aluminum foil with a thickness of 7μm should be less than 200 holes/square meter; the number of pinholes in the aluminum foil with a thickness of 9μm should be less than 100 holes/square meter. square meters. No matter how thick the aluminum foil is, the pore size of the pinhole should not be larger than 20μm. 3. The texture of the aluminum foil should be soft, it should not be easy to break when folded, and it should have good toughness. The purchased aluminum foil should be stored in a dry state, and should not be stored for too long.