How long can edible fungi be stored at room temperature?

I. Storage and freshness-retention characteristics and varieties of mushrooms

Mushrooms are rich in amino acids and protein and have a delicious flavor. However, after harvest, mushrooms respire vigorously and at room temperature quickly open their caps, turn brown, develop off-flavors, and deteriorate in quality, so they can only be stored short-term. Dried mushrooms are easy to preserve, but their nutritional value decreases, and if processing is not carried out in time, serious losses can occur. Therefore, after harvest, measures must be taken during storage, transport, sale, and before processing to prevent a decline in mushroom quality. There are many cultivated varieties of mushrooms, and common ones include oyster mushroom, shiitake, button mushroom, enoki mushroom, and straw mushroom.

II. Harvesting

1. Timely harvesting: If mushrooms are harvested too early, the caps have not grown fully, which affects yield; if too late, the fruiting bodies do not keep well and quality declines. Oyster mushroom should be harvested when the caps are fully expanded, the color has become lighter, white fluffy material is present in the depressed center, and the edges have just begun to curl upward, but before large numbers of spores are released. If harvested too late, the stipes become hard, the edges crack, the texture becomes tough, and it often has a bitter and unpleasant taste, reducing eating quality. Shiitake should be harvested before the veil opens. Button mushroom is generally harvested before the cap exceeds 4 cm and before the veil opens; if harvested too late, it easily opens and turns brown, shortening the storage period. Enoki mushroom should be harvested when the stipes stop growing, the cap diameter reaches 1.5--2.0 cm, and the cap edges begin to flatten; if too late, the fruiting bodies lose weight.

2. Harvesting method: Do not spray water on the day of harvest in order to maintain firmness, but stopping water too early will cause the caps to dry out and become brittle and cracked; in some cases a small amount of water may be sprayed in the early morning. When harvesting, turn each mushroom upward and tilt the cap outward; do not pull it directly from the bed. Pinch the base of the fruiting body tightly with the fingers of the left hand, and cut off the base of the stipe with a knife in the right hand; when fruiting bodies grow in clusters, such as with oyster mushroom, cut the whole cluster at the base of the stipes with a knife close to the bed surface; for enoki mushroom, simply grasp the cluster gently and pull it out. After harvest, place the mushrooms in a basket with the stipes facing up, and precool them as soon as possible or trim and grade them in a cold place; they may also be trimmed immediately after harvest and then put into baskets. For varieties with larger fruiting bodies and shorter stipes, shortening the stipes can prolong the storage period. For example, after harvest, oyster mushroom is best left with a stipe length of 2--3 cm. When button mushroom is harvested, the stipe length is generally 5--10 mm. The main edible part of enoki mushroom is the stipe, so it should not be shortened. During trimming, remove opened mushrooms, diseased mushrooms, insect-damaged mushrooms, and mechanically damaged mushrooms that are unsuitable for storage. After trimming, refrigerate the mushrooms as soon as possible.

III. Storage and freshness-retention conditions

The suitable conditions for mushroom storage are 0°C and 95% relative humidity. Water loss in mushrooms is related to black stipes and cap opening, and packaging with film or maintaining relative humidity above 95% can reduce water loss. Controlled-atmosphere storage can inhibit browning in mushrooms; controlling oxygen at 2--4% and carbon dioxide at 5--10% helps maintain the whiteness of mushrooms and prolong storage life. Treatment with brine, citric acid, ascorbic acid, sulfur dioxide, or steam heat can inactivate polyphenol oxidase activity and prevent enzymatic browning; during storage and transport, metal containers should be avoided for holding mushrooms in order to prevent non-enzymatic browning.

IV. Storage, freshness retention, and treatment methods

1. Controlled-atmosphere storage: (1) Spontaneous modified atmosphere: Place mushrooms in polyethylene bags 0.04--0.06 mm thick, using the mushrooms' own respiration to create a low-oxygen and high-carbon-dioxide environment inside the bag. The bags should not be too large; generally a capacity of 2--4 jin is suitable, and quality remains unchanged for 5 days at 0°C. (2) Carbon dioxide flushing: Place mushrooms in polyethylene bags 0.04--0.06 mm thick, fill with nitrogen and carbon dioxide, and keep them at 2--4% and 5--10% respectively; at 0°C this can inhibit cap opening and browning. (3) Vacuum packaging: Place mushrooms in polyethylene bags 0.06--0.08 mm thick and vacuumize to reduce oxygen content; at 0°C they can be kept for 7 days.

2. Ice storage method: During transport, add ice cubes to cool the fruiting bodies. Line the packaging container with a layer of plastic film, place 4--6 cm of crushed ice at the bottom, place ice packs in the middle, and arrange mushrooms around the sides. When filled to about 80% capacity, fold the surrounding film inward, cover the film with crushed ice about 5 cm thick, and finally cover and transport.

3. Crock storage method: Place cold water 3--4 cm deep in the bottom of a washed crock, set a wooden rack above it, stack the mushrooms on the rack, then seal the opening with plastic film and store at low temperature.

4. Chemical treatment: (1) Brine. After harvest, wash mushrooms with 0.6% cold brine and soak them for 10 minutes, which can precool them and help prevent browning; drain off the water and store. If, after washing with brine, they are then rinsed with 0.1% ascorbic acid or 0.1% citric acid before storage, the effect is even better. Drain them, put them in plastic bags, and refrigerate. (2) Sodium metabisulfite. After harvest, wash away debris with 0.02% sodium metabisulfite, then place them in 0.05% sodium metabisulfite for half an hour, rinse with clean water, drain, and store; this has a very good color-protecting effect.

5. Irradiation

Gamma-ray irradiation can prevent fresh mushrooms from changing color and inhibit respiration and cap opening, with a dosage of 200--300 rad.