What are the key points of preservation technology for exported fresh shiitake mushrooms?

Fresh shiitake mushrooms are not only very popular on the international market, but their price has consistently remained at -- 28 yuan RMB, with the foreign CIF price at 5-7 US dollars per kilogram. Therefore, preserved fresh shiitake mushroom exports have become another new project with high efficiency in earning foreign exchange, but exported fresh shiitake mushrooms must preserve to the greatest extent the product's natural color, shape, and the good texture of smooth caps and crisp stems. Therefore, exported fresh shiitake mushrooms must, according to international market requirements, do the following well:

1. Harvest fresh mushrooms well. To avoid fresh mushrooms having too high a water content, which causes the mushroom surface to turn black and quality to decline, do not spray water on the logs one day before harvest, and avoid harvesting on rainy days. Suitable times for harvesting mushrooms: summer mushrooms should be harvested once in the morning and once in the evening each day, while winter mushrooms should be harvested in the morning. This is because at these times the temperature is lower, the metabolic activity of the mushroom body is slow, and the fresh mushrooms are less likely to open their veils, ensuring quality. At the same time, harvesting must be carried out according to fresh mushroom export standards: namely, complete fruit body shape, thick and plump mushroom flesh, white unbroken partial veil (70% mature) or slightly open (80% mature) or large rolled edge (90% mature), free of clay, free of damage, free of deformities, free of pests and diseases, maintaining a beautiful naturally grown posture. Harvested fresh mushrooms should be placed in a plastic basket lined with a large square piece of gauze, and after harvesting is complete, the gauze should be tied diagonally corner to corner while awaiting processing.

2. Dehydration (moisture removal) of fresh mushrooms. Generally, fresh mushrooms have excessive water content and do not meet export standards. If the water content is too high, during stacking, storage, and transport, the physiological metabolic activity of the mushroom body will generate heat and raise the temperature, reducing commercial value. Generally, exported fresh shiitake mushrooms are divided into large and small packaging. Large packaging requires a water content of 70%-80%, while small packaging requires 80-90%. The dehydration (moisture removal) methods for fresh mushrooms include:

(1) Natural sun-drying to reduce moisture. That is, place the fresh mushrooms on a drying curtain with the caps tilted upward and evenly arranged, and dry them in the sun with ventilation. Autumn and winter mushrooms are dried for 3-6 hours, spring mushrooms for 6-7 hours, and summer mushrooms for 1.0-1.5 hours (but this should be flexibly controlled according to the water content of the mushroom body; generally, the standard is that when the stem is pinched by hand there is no moist feeling and the mushroom base has slightly shrunk).

(2) Rotary hot-air moisture removal. Place the mushrooms evenly spread on a drying curtain with the caps facing downward, and place them in a self-made hot-air (40°C) rotary kiln for moisture removal.

(3) Use a moisture-removal machine for moisture removal. Fresh mushrooms treated by this method have good color and high quality, but the investment is large. However, no matter which moisture-removal method is used, the dehydrated fresh mushrooms must be placed in plastic crates, moved into a 1-4°C cold storage for pre-cooling, and continue to be cooled and dehumidified, stored, and kept waiting for packaging.

3. Packaging requirements. According to customer requirements, first grade the dehydrated mushrooms in the cold storage by size, trim the stems, weigh them, pack them separately into plastic baskets, and put them back into the cold storage for two hours before packaging. Packaging is divided into two types, large and small. Large packaging is divided by cap diameter into Grade L (diameter 6 cm or more), Grade M (diameter 5 cm or more), and Grade S (diameter 4 cm or more). When packaging, put them according to grade into transparent non-toxic film bags, vacuum-seal them, then place them into heat-insulating plastic foam boxes, and wrap the outside with corrugated cardboard boxes. Each box has a net weight of 5 kg or 10 kg. Finally, seal the box opening with adhesive tape and mark the grade, weight, and shipping date. Small packaging is to place fresh mushrooms on a tray in a plastic box, with a net weight of 100 g per box, and 4, 5, 6, or 8 mushrooms can be packed. The gills must face upward and be arranged neatly, then sealed on the outside with special plastic cling film, then packed by size grade into cartons, sealed with adhesive tape, marked with grade, weight, and shipping date, and stored in cold storage awaiting transport.

4. Product transport. After packaging, fresh mushrooms must be promptly shipped to the port (airport and seaport). When the temperature is below 15°C, ordinary vehicles can be used for transport; otherwise, refrigerated vehicles (1-3°C) must be used. Since fresh mushrooms are mainly sold to Japan and Singapore and other places, the supplier must consider calculating both domestic and foreign transport time and the seller's @#@136@#@ time within the effective preservation period of the fresh mushrooms, so as to avoid quality decline caused by the mushroom body opening its veil. The effective preservation period of shiitake mushrooms differs under different temperature conditions: when the temperature is 10°C, preservation is 18 days; at 6°C, 14 days; at 15°C, 7 days; and at 20°C, 4 days. In short, the higher the temperature, the shorter the preservation time; conversely, the longer the preservation time.