Comprehensive knowledge of the best canned food pa

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Comprehensive knowledge of canned food packaging, preservation and storage 5

(I) liquid injection

in addition to liquid food, paste, surimi and dry food, most food should be filled with liquid juice after canning. The liquid added varies according to the variety of cans. Some add water, such as water Horseshoe; Some are filled with sugar liquid, such as sugar apple; Some are filled with salt water, such as mushrooms, green beans, etc; Some are filled with seasoning liquid, such as braised pork, and so on. The role of filling juice has been mentioned earlier

(II). Pre sealing

some canned foods should be pre sealed before venting after canning

the so-called pre sealing is to preliminarily hook the tank body with a sealing machine, and its tightness is such that the tank cover can rotate along the tank body without falling off. At this time, the air can circulate. In the process of hot exhaust or vacuum sealing, the gas in the tank can be avoided freely, and the tank cover will not fall off

effect of pre sealing: p130, 5 points

if the vacuum can sealing machine is directly used to seal the can, pre sealing is not required

(III) exhaust

after filling the cans with liquid, exhaust the air before sealing the cans to eliminate the air in the cans and food tissues as much as possible, so that a certain degree of vacuum can be formed after the cans are sealed to prevent deterioration, which is helpful to ensure and improve the quality of canned food

1. Purpose of exhaust

① inhibit the activity of aerobic microorganisms and their growth and development

② reduce the changes of food color, aroma and taste, especially the oxidative loss of vitamins and other nutrients

③ reduce the influence of content expansion on container tightness during heating and sterilization, and ensure the safety of suture

④ keeping vacuum inside the can can can keep the bottom cover of the solid can flat or inward, which is the appearance sign of normal and good canned food

this is different from the tank expansion caused by gas produced by microbial spoilage

⑤ after removing the air, the above reduction of the container is related to the general precautions of the universal tensile testing machine. Rust corrosion

because there is oxygen in the air, it will accelerate the corrosion of the iron sheet. The exhaust of the can reduces the residual oxygen content and slows down the corrosion of the inner wall of the can

2. Vacuum degree and measurement

a. vacuum degree - vacuum degree of canned food refers to the difference between the atmospheric pressure outside the tank and the pressure inside the tank

that is, vacuum degree = atmospheric pressure - residual pressure in the can

commonly used mmHg means

a simple can vacuum gauge is commonly used as a measuring tool for can vacuum degree, which is more accurate, but it has a destructive effect on cans. This vacuum gauge has a sharp needle at the lower end, and a rubber pad at the back of the sharp needle is used for sealing. When measuring, the sharp needle is inserted through the can cover to measure the vacuum of the can, which is often used by the inspection department for testing

a non-destructive can vacuum automatic detector, which is actually a photoelectric technology detector

in addition, manual inspection can also be used, that is, knock with a small wooden strip and judge by echo. Judge the vacuum degree of the can according to the clear and turbid sound when the stick hits the bottom cover of the can. When the production scale is small, this is a commonly used vacuum degree detection method

b. influencing factors of vacuum degree

① the time and temperature of exhaust are important factors determining the vacuum degree of cans

the exhaust time is long, the temperature is high, the gas retained in the tank and raw materials is discharged more thoroughly, and the vacuum formed after the tank is sealed and cooled is also higher

② after the can is vented, the time interval before sealing also affects the vacuum of the can, that is, the temperature of canned food that makes us different when sealing, also known as the sealing temperature. If the time is prolonged, therefore, the cover should be quickly sealed after venting to maintain a higher temperature when sealing the tank

③ the size of the top gap in the tank

for vacuum sealing exhaust and steam sealing exhaust, the vacuum degree of the can increases with the increase of the top gap. The larger the top gap, the higher the vacuum degree of the can

for heating exhaust, the influence of the top gap on the vacuum degree of the can is that with the decrease of the top gap, the vacuum degree of the can is higher

④ types and freshness of food raw materials

all kinds of raw materials contain a certain amount of air. The types of raw materials are different, and the air content is also different. After the cans are cooled by exhaust, the residual air in the tissue will be gradually released during storage, which will reduce the vacuum degree of the cans. The higher the air content of raw materials, the more serious the vacuum degree reduction

the degree of raw material also affects the vacuum degree of cans. Because some tissue components of stale raw materials have changed, high temperature sterilization will promote the decomposition of these components and produce various gases, such as H2S, NH3, etc. from the decomposition of food containing protein, and CO2 from fruit and vegetable foods. The generation of gas increases the pressure in the tank and reduces the vacuum

⑤ acidity of food

the level of acid content in food also affects the authenticity of cans. In China, H3PO4 iron Li, 3-yuan, cobalt acid Li materials are the main hollow materials. When the acidity of food is high, it is easy to interact with the inner wall of the metal tank to produce hydrogen, which increases the pressure in the tank and decreases the vacuum degree. Therefore, for foods with high acidity, it is best to use paint cans to prevent acid from corroding the inner wall of the cans and ensure the vacuum of the cans

⑥ changes in external conditions will also affect the vacuum degree in the tank

when the external temperature rises, the residual gas in the tank is heated, the expansion pressure increases, and the vacuum degree decreases. The higher the outside temperature, the lower the vacuum degree of the can

the vacuum degree of cans is also affected by atmospheric pressure. As the atmospheric pressure decreases, so does the vacuum. Therefore, the altitude also affects the vacuum degree. The higher the altitude, the lower the vacuum degree

in addition, from the perspective of safety production, a higher vacuum degree (mmHg) can be maintained for small tanks, while a slightly lower vacuum degree (mmHg) should be maintained for large tanks. Because keeping the vacuum degree too high in the large tank will cause serious tank deformation, and the tank wall will be subject to excessive pressure and collapse inward. (to be continued)

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