Fertilization Techniques and Methods for Edible Fungi and the General Process of Canning

Process flow:

Acceptance of raw mushrooms → rinsing → precooking → grading → filling into cans → adding broth → pre-seaming → exhausting and sealing → sterilization and cooling → wiping the cans → inspection → packaging.

Key operating points:

1. Acceptance of raw mushrooms: Fresh mushrooms discolor and open their caps very easily after harvesting, so the handling of fresh mushrooms from harvest to filling into cans should be as rapid as possible to reduce exposure time to the air.

To ensure canned product quality, acceptance must be carried out strictly according to canned product specifications; immediately after acceptance, the mushrooms should be immersed in 2% dilute brine or 0.03% sodium metabisulfite solution, with the mushroom bodies kept from floating above the liquid surface, and transported quickly to the factory for processing.

2. Rinsing: also called color protection.

Harvested fresh mushrooms should be soaked in the rinsing solution promptly for rinsing. The purpose is to wash off mud and impurities on the mushroom surface, isolate them from the air, inhibit the oxidation by tyrosinase in the mushroom bodies, prevent discoloration of the mushroom bodies and keep their color normal; inhibit protease activity, stop the mushroom bodies from continuing to grow and develop, and keep agaric mushrooms in their original shape.

Rinsing solutions include clean water, dilute brine (2%) and dilute sodium metabisulfite solution (0.03%), etc.

To ensure the rinsing effect, the rinsing solution should be replaced periodically; depending on the turbidity of the solution, replace it once every 1-2 hours of use.

3. Precooking: that is, blanching. After the fresh mushrooms are rinsed clean, scoop them out promptly and boil them in boiling dilute brine or dilute citric acid solution for about 10 min, until cooked through.

Purpose of precooking: destroy enzyme activity in the mushroom bodies, expel air from the mushroom tissue, and prevent the mushroom bodies from oxidative browning; kill the cells of the mushroom tissue and prevent umbrella-shaped mushrooms from opening their caps; destroy the cell membrane structure and increase membrane permeability to facilitate penetration of the broth; soften the mushroom tissue, shrink the mushroom bodies, enhance plasticity, facilitate canning, and reduce damage to the caps. After precooking is completed, immediately place them in cold water to cool.

Because the mushroom bodies of edible fungi contain sulfur-containing amino acids, which easily react with iron to form black iron sulfide, the precooking vessel should be made of aluminum or stainless steel.

4. Grading: To make the mushroom bodies in the cans basically uniform in size, grading is still required before filling. Grading can be done manually or mechanically.

5. Filling into cans: The processed mushroom bodies should be filled into cans as quickly as possible to prevent secondary microbial contamination. When filling, care should be taken that the mushroom bodies are basically consistent in size, shape and color, the filling amount should be as accurate as possible, and a certain headspace should be left. The so-called headspace refers to the distance between the surface of the mushroom bodies in the can and the can lid. Raw material filling can be done manually or mechanically.

6. Adding broth: After the mushroom bodies are filled into the cans, a certain amount of broth is injected. Its purpose is to improve flavor, raise the initial temperature of the mushroom bodies in the can, change the heat transfer mode inside the can, shorten the sterilization time, and increase the vacuum degree inside the can.

The type, concentration and amount of broth added vary with different species of edible fungi. Refined brine or brine acidified with citric acid is commonly used. The broth temperature is required to be about 80°C. Broth is generally added with a liquid filling machine.

7. Pre-seaming: After the raw materials are filled into the cans, pre-seaming should be carried out before exhausting to prevent the mushroom bodies in the can from expanding due to heating and falling out of the can, and to prevent the broth from spilling over during heated exhausting. Pre-seaming uses a can seaming machine; the rollers of the seaming machine initially interlock the cover hook of the can lid with the body hook of the can body. The tightness of the interlocking is such that the can lid can freely rotate along the can body but cannot separate from the can body, so that during exhausting, gases such as air and water vapor in the can can freely escape from inside the can.

8. Exhausting and sealing: To prevent the growth and reproduction of aerobic bacteria and molds in the cans, prevent deformation and damage of the containers caused by air expansion during heat sterilization, and reduce the loss of nutrients in the mushroom bodies, etc., the air in the cans should be removed as much as possible before sealing. Commonly used exhausting methods include the heated exhausting method and the vacuum can-sealing exhausting method.

9. Sterilization and cooling: Canned edible fungi should be cooled rapidly to about 40°C after high-temperature sterilization. The main process conditions of the heating-up stage, constant-temperature stage and cooling stage in the can sterilization process, written together continuously in the prescribed format, are called the sterilization formula. For example, the sterilization formula of a certain canned product is 10′-23′-5′/121°C.