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