The purpose of blanching

Blanching cleanse the products. It shrinks the product, providing for a better fill of the container and removing gases, thus allowing better vacuum after sealing.

Commercial blanching conditions typically involve heating at 95-100 °C for 3 to 10 minutes, depending on the type and size of material to be blanched.

The blanching process also destroys enzymes in the food that otherwise might react during the initial heating in the retort and produce undesirable flavors or discoloration or cause loss of vitamin C.

When very high-temperature, very short-time methods of heat processing are used, enzymes might not be inactivate, which would cause development of off-flavors in the food. This can be prevented by blanching. The conditions of blanching are chosen so as to ensure inactivation of the enzymes responsible for oxidation while minimizing loss of sensory quality and nutrients.

Blanching tends to fix the natural color of vegetables and it provides a clearer brine in the canned products.

Good canning practice demands a high level of hoppers and fillers handling vegetables hot from blanching. This is essential in order to prevent the undesirable build up of thermophilic bacteria.
The purpose of blanching

Food pretreatment before processing

It is generally necessary for foods to undergo a treatment prior to the canning process, but these pretreatment differ depending on the foods.

The purpose of pretreatment is to help preserve color nutrients, flavor and overall quality.  Specific vegetables and fruits are high in different vitamins. It is important to know how the vitamin is destroyed and what pretreatment will stop the loss.

Some pretreatment are applied to many different foods. One of these, usually applied to vegetables, is blanching. Vegetables may be pretreated before drying, just as they are before freezing, by blanching in boiling water or steam.

Blanching is steam or water is a method of partially cooking the food, typically just to the point of inactivating the enzymes and also used to break the skins of fruits that have a waxy coating.

Steam blanching preserves more of the food’s natural vitamins and minerals than water blanching but requires slightly longer processing period.

Vegetables are first washed, usually in water and detergent, then rinsed. They are then passed over belts, where any remaining foreign matter, such as weeds or stalks, can be removed by hand.

Blanching consists of heat in steam (no pressure) or hot water (usually about 98.9 ° C) until the temperature of the food is brought up to about 82.2 C – 87.8 ° C in all parts, the cooling in water.

Some vegetables cannot be blanched at these high temperatures without adversely affecting their taste and texture. In such cases, catalase is used as the test enzyme for sufficiency of blanch.

Off flavors may result, though even in the absence of catalase, if peroxidase is present.
Food pretreatment before processing