Key processes in canning of fruits and vegetables

Speaking of the key processes of canning, most people think of sealing and sterilization. For canned fruits and vegetables, there is a key process that is important and often overlooked.

This key process is pre-cooking of raw materials for fruits and vegetables before canning.

Most of the raw materials for fruits and vegetables are pre-cooked during processing. This treatment takes a short time and the temperature is not too high. This type of process is also known as "scalding", mainly by immersing the raw materials in hot water or boiling water for a certain period of time or bringing them into contact with steam. Pre-cooking of raw materials for fruits and vegetables has the following effects:

1. Inhibition of enzyme activity: Since the enzymes in plants are inhibited, oxidation and other chemical reactions are also inhibited, thereby avoiding color and flavor changes of raw materials, reducing the loss of certain vitamins, improving product quality, and maintaining a certain level. Nutritional ingredients.

2. Discharge the gas in the raw material: The raw material of the fruit and vegetable often contains a certain amount of gas, and the gas is removed after pre-cooking, so that the product has a high degree of vacuum, and the integrity of the can be curled in the heat sterilization.

3. Softening the food raw materials: Before the raw materials are not pre-cooked, the tissues are often hard and bulky, and after sealing and sterilization, the raw materials are softened and shrunk in the tank, often forming large gaps, and the amount of cans is filled. Can not meet the requirements. After the raw materials are pre-cooked, the tissue shrinks and the volume is reduced, which facilitates canning.

4, easy to process: raw materials after pre-cooking treatment, in the peeling, dicing, correction and other processing is much more convenient, can significantly improve efficiency.

5, can improve the quality of raw materials: the raw materials can be kept in a certain color, some raw materials have a special smell, after pre-cooking can remove this unpleasant smell, some vegetables in boiling water will lose their vivid green If the pre-cooking treatment is carried out first, and then sterilized, the original color can be better maintained.

6, the cleanliness of raw materials: the role of raw material washing, can significantly reduce microbial contamination.

Pre-cooking of raw materials is hot water treatment and steam treatment. Due to the variety of raw materials for fruits and vegetables, the pre-cooker types designed are also different. The temperature of hot water treatment is usually below the boiling point or boiling point, and the steam treatment is mostly by spraying. The effect of hot water treatment is better. After the raw materials are put into hot water, the raw materials are in contact with hot water, and the pre-cooking is rapid and uniform. The disadvantage is that the amount of water is large, the raw materials are in direct contact with hot water, and some water is soluble. Food ingredients such as vitamins and minerals, etc., which are beneficial to human nutrition, are easily lost. Due to the loss of these water-soluble nutrients, the biological oxygen consumption in the discharged waste liquid is sometimes increased, causing environmental pollution. In the steam pre-cooking treatment, only a small amount of condensed water is generated when the steam is in contact with the raw material, so the nutrient component is lost much less, and the wastewater discharge after treatment is less, and the quality of the raw material after pre-cooking is better.

The simple equipment for hot water pre-cooking is a metal water tank equipped with a steam heating tube. The water temperature can be controlled. The raw material is immersed in water in a metal basket for a certain period of time. This is a batch device. , low efficiency. Then there is a continuous hot water pre-cooking machine. The fuselage is a long-shaped water tank equipped with a steam heating tube. There is a circulating conveyor belt in the tank. After the raw material enters, it falls evenly on the conveyor belt and enters the hot water. The purpose of cooking. The drum pre-cooking machine is one step further than the general continuous hot water pre-cooking machine. Its outer casing is cylindrical, the outer casing is filled with hot water, and a rotating cylinder is arranged inside the casing. Full of small holes, there is a spiral partition inside the tube. About half of the inner cylinder is immersed in the hot water of the outer casing, and after the raw material enters the inner cylinder, it travels along the spiral as the rotation advances, thereby completing the pre-cooking.

There are many types of steam pre-cookers, usually in a closed condition, pre-cooked by steam injection. In order to improve the effect of pre-cooking, all parts of the raw material should be subjected to steam at the same time.