Detailed Explanation of Key Techniques for Winter Storage of Napa Cabbage
Winter Storage Techniques for Napa Cabbage
There are many methods for storing napa cabbage, mainly cellar storage, ventilated storage, and pit storage, as well as mechanically assisted ventilation or mechanical refrigeration storage in large warehouses.
1. Pit storage Suitable for winter napa cabbage storage in southern Northeast China, southern North China, and Shandong and Henan provinces. Dig a shallow trench with a depth roughly equal to the height of the cabbage and a width of about 1 m; length is unlimited. The dug trench should be left to dry for 2-3 days to reduce humidity.
Place the napa cabbage in the trench with the roots facing downward and the tops level, so that the soil cover will be uniform in thickness. When burying, it should be done on a cloudy day or in cooler weather as much as possible, so that a lower temperature is maintained in the trench. After the cabbage is arranged, decide whether to cover it and how thick the cover should be based on the weather conditions at the time. Generally, in the early storage period, when the temperature is relatively high, no cover may be applied, or a small amount of covering material may be used for shade. As the weather gradually turns colder, dry soil can be used for covering, and moist clods of soil should be avoided as much as possible. Soil should be added in stages, with the thickness generally controlled on the principle that the napa cabbage is not damaged by heat and the soil cover is not frozen through.
In areas with a thinner frozen soil layer, an inverted method can also be used for storage. Place the selected napa cabbage vertically in the prepared trench with the roots facing upward and cover with soil (just enough to bury the roots), then pour a small amount of water on the soil surface so that the cabbage maintains weak growth during storage. This inverted burial method is suitable for storing napa cabbage that is about 70% headed. Inverted pit storage makes the cabbage less likely to freeze and can increase weight; however, care should be taken not to dig the trench too deep or too wide, and not to apply too thick a soil cover.
Using the pit storage method to store napa cabbage is simple and easy to carry out, with little water loss and small weight loss; however, it does not allow ventilation, is not easy for regulating temperature and humidity, and has a relatively short storage period.
2. Cellar storage Cellar storage of napa cabbage is relatively common, but the methods differ from region to region. The south is warmer, so aboveground cellars are mostly used; the cold northern regions mostly use underground cellars; and the Central Plains region mostly uses semi-underground cellars.
Send the pretreated napa cabbage into the cellar for stacking. Generally, stacks are made along the length of the cellar, one cabbage wide and about 2 m high, and several stacks can be made in one cellar. To prevent the stacks from collapsing, wooden poles or simple wooden frames can be used for support, and a certain distance should be kept between stacks for ventilation and management. The methods of arranging cabbage vary widely from place to place, but all should follow the principles of facilitating ventilation without heat damage, facilitating insulation without freezing, facilitating stacking without collapse, and facilitating management without wasting labor, with few turnings and low losses of all kinds.
For stacked napa cabbage, there is generally a relatively large temperature difference between the top and bottom. At regular intervals, the stack should be turned once, moving the upper cabbage to the lower part to balance temperature and humidity, and at the same time removing from the cellar the cabbage that is no longer suitable for continued storage.
Management during the storage period can be roughly divided into three stages: the early storage period (from being put into the cellar to "Major Snow"), when the cellar temperature is relatively high and the cabbage releases more heat through respiration, the vents should be opened every day when the outside temperature is lower than the cellar temperature, so as to lower the cellar temperature and expel harmful gases. At this time, turning the cabbage should be done frequently, and the interval between turnings should gradually be extended afterward. The middle storage period ("Major Snow" to "Start of Spring") is the cold season, when both the cellar temperature and the cabbage temperature have already dropped, and the respiration heat of the cabbage decreases, so the main task is to prevent freezing; close the vents, and if necessary, carry out short periods of ventilation at noon when the temperature is relatively high. During this period, reduce the number of turnings and extend the interval between turnings, and try to protect the outer leaves during turning so as to protect the inner leaves. In the late storage period (after "Start of Spring"), the temperature gradually rises, and the cellar temperature rises accordingly, so ventilation should mainly be done at night to lower the cellar temperature. During this period, turning the cabbage should be done frequently.
1. Pit storage Suitable for winter napa cabbage storage in southern Northeast China, southern North China, and Shandong and Henan provinces. Dig a shallow trench with a depth roughly equal to the height of the cabbage and a width of about 1 m; length is unlimited. The dug trench should be left to dry for 2-3 days to reduce humidity.
Place the napa cabbage in the trench with the roots facing downward and the tops level, so that the soil cover will be uniform in thickness. When burying, it should be done on a cloudy day or in cooler weather as much as possible, so that a lower temperature is maintained in the trench. After the cabbage is arranged, decide whether to cover it and how thick the cover should be based on the weather conditions at the time. Generally, in the early storage period, when the temperature is relatively high, no cover may be applied, or a small amount of covering material may be used for shade. As the weather gradually turns colder, dry soil can be used for covering, and moist clods of soil should be avoided as much as possible. Soil should be added in stages, with the thickness generally controlled on the principle that the napa cabbage is not damaged by heat and the soil cover is not frozen through.
In areas with a thinner frozen soil layer, an inverted method can also be used for storage. Place the selected napa cabbage vertically in the prepared trench with the roots facing upward and cover with soil (just enough to bury the roots), then pour a small amount of water on the soil surface so that the cabbage maintains weak growth during storage. This inverted burial method is suitable for storing napa cabbage that is about 70% headed. Inverted pit storage makes the cabbage less likely to freeze and can increase weight; however, care should be taken not to dig the trench too deep or too wide, and not to apply too thick a soil cover.
Using the pit storage method to store napa cabbage is simple and easy to carry out, with little water loss and small weight loss; however, it does not allow ventilation, is not easy for regulating temperature and humidity, and has a relatively short storage period.
2. Cellar storage Cellar storage of napa cabbage is relatively common, but the methods differ from region to region. The south is warmer, so aboveground cellars are mostly used; the cold northern regions mostly use underground cellars; and the Central Plains region mostly uses semi-underground cellars.
Send the pretreated napa cabbage into the cellar for stacking. Generally, stacks are made along the length of the cellar, one cabbage wide and about 2 m high, and several stacks can be made in one cellar. To prevent the stacks from collapsing, wooden poles or simple wooden frames can be used for support, and a certain distance should be kept between stacks for ventilation and management. The methods of arranging cabbage vary widely from place to place, but all should follow the principles of facilitating ventilation without heat damage, facilitating insulation without freezing, facilitating stacking without collapse, and facilitating management without wasting labor, with few turnings and low losses of all kinds.
For stacked napa cabbage, there is generally a relatively large temperature difference between the top and bottom. At regular intervals, the stack should be turned once, moving the upper cabbage to the lower part to balance temperature and humidity, and at the same time removing from the cellar the cabbage that is no longer suitable for continued storage.
Management during the storage period can be roughly divided into three stages: the early storage period (from being put into the cellar to "Major Snow"), when the cellar temperature is relatively high and the cabbage releases more heat through respiration, the vents should be opened every day when the outside temperature is lower than the cellar temperature, so as to lower the cellar temperature and expel harmful gases. At this time, turning the cabbage should be done frequently, and the interval between turnings should gradually be extended afterward. The middle storage period ("Major Snow" to "Start of Spring") is the cold season, when both the cellar temperature and the cabbage temperature have already dropped, and the respiration heat of the cabbage decreases, so the main task is to prevent freezing; close the vents, and if necessary, carry out short periods of ventilation at noon when the temperature is relatively high. During this period, reduce the number of turnings and extend the interval between turnings, and try to protect the outer leaves during turning so as to protect the inner leaves. In the late storage period (after "Start of Spring"), the temperature gradually rises, and the cellar temperature rises accordingly, so ventilation should mainly be done at night to lower the cellar temperature. During this period, turning the cabbage should be done frequently.