Post Harvest Processing
Introduction
Mushrooms are best consumed as fresh. However, in actual practice this is may not be possible. The storage at high temperature results in browning. Mushrooms have a high rate of respiration and hence proper attention should be given for storage. Some of the commonly adopted methods are described hereunder:
1) Refrigeration/ Instant packing:
Freshly harvested mushrooms are packed in 25 gauge polythene bags without making any holes. Immediately after packing they are stored at 5°C in a refrigerator. This process extends the storage life for 3-5 days. This process helps in reducing the respiratory rate and minimizing the water loss. In addition, it reduces browning of mushroom and off flavour development.
2) Freeze-drying:
The mushrooms are sliced and immersed in 0.05 per cent sodium meta bisulphite and 2 per cent common salt solution for 30 minutes. They then blanched in boiling water for 2 minutes, followed by cooling. This then frozen for one minute at -12°C and store at –20°C. This process extends the storage life for 3-4 months.
3) Dehydration:
This treatment involves three steps viz., Pretreatment, drying and storage.
a) Pre treatment:
- Clean the mushroom and blanch it in boiling water for 2 minutes and immerse it in cold water for 2 minutes.
- Dip the mushroom in water containing 0.2 per cent potassium meta bisulphite and 1 per cent citric acid and use for drying.
b) Drying:
- Sun drying: The pre treated mushroom is dried in open sunlight till it reaches 1/10th weight of the fresh product. After drying, it can be stored for 3 months, however colour may turn to brown and appearance of the final product is not good.
- Drying in flow drier: Dry the pre treated mushroom at 60°C with heated air for 6-8 hr. This process lead to bring the final moisture level to 3-5%.
- Vacuum drying: Dry the pre treated mushroom at 40°C under vacuum condition instantly. This process yield a very good quality mushrooms but cost of processing is heavy.
4) Canning:
Canning is adopted on a very large scale, especially for preservation of button mushrooms. For canning purpose, the mushrooms should be harvested at an early stage. The mushrooms of uniform size are selected and stalks are cut before processing.
Procedure:
- Wash the mushroom in clean water to remove dirt and other foreign materials.
- Dip the mushroom in boiling water for 2 minutes, take it out and dip in cold water for 2 minutes.
- Fill the mushrooms in the specially made cans upto ¾ capacities. (Approximately 220-g mushrooms are filled in 1-lb cans)
- Add salt solution consisting of 2 per cent common salt, 2 per cent sugar and 0.3
per cent citric acid just to fill up to the brim. (Before adding, the salt solution should be boiled and filtered through muslin cloth) (Approximately 125 ml. solution is needed for 1 lb can).
- Place the lid on the can and keep the cans in boiling water or steam till the temperature in the centre of the cans reaches 80-85° C.
- Seal the can on a seamer to get an air tight seam.
- Sterilize the cans in an autoclave at 10 lb. pressure for 20-25 minutes.
- Keep the cans immediately after sterilization in clean cool water for cooling.
- Wipe the cans with a dry cloth and store in a cool dry place. This process extends the storage life up to 12 months.
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