Methods for obtaining vacuum in canned food

(1) Heating and exhausting method
Put the food into the can while it is still hot, or heat the can through an exhaust box, and use the expansion of the water vapor and air in the food to displace the air. In addition, the proportion of water vapor in the gas increases and the oxygen decreases relatively. The can is sealed immediately while it is still hot, and a certain vacuum is formed after cooling.
Here, attention should be paid to the control of food temperature, temperature in the food can, and exhaust time. It should be determined according to the actual situation such as food variety, can type, can capacity, and material. The temperature should be based on the center of the can, and the exhaust time should be based on the exhaust effect and the comprehensive consideration of maintaining food quality.
(2) Vacuum can sealing and exhausting method
During the can sealing process, a vacuum pump is used to extract the gas in the seal to form a certain vacuum. When the can enters the sealed vacuum chamber of the can sealing machine, the gas in the can immediately overflows, and then it is quickly sealed, so that a certain vacuum is obtained in the can. This method is often used for foods that are not suitable for heating. Here, attention should be paid to the sealing vacuum degree, as well as the time control from the can entering the sealing chamber to the can sealing, to avoid overflow of the filling and insufficient exhaust.
(3) Steam jet exhaust method
After the can is pre-sealed, steam is jetted into the top gap of the can to displace the air in the top gap, and the can is immediately sealed. The top gap is mainly filled with steam, and a vacuum is obtained after condensation. Therefore, the jetted steam must have a certain pressure and temperature, and the entire jetting must continue until the sealing is completed. In this method, it is important to have an appropriate top gap in the food can, generally 8-10 minutes. The temperature of the canned food is increased, which is conducive to obtaining a higher vacuum degree.
(4) Gas replacement exhaust method
A method of filling the top gap of the food can with a suitable protective gas to displace the original air. The principle is similar to steam jet exhaust, except that the protective gas, such as CO2, N2, etc., is not steam.