Digging the cellar is hard work. Generally, it is decided to dig cellars of different sizes according to the family population and demand. There are round wine cellars and square wine cellars. Smaller round cellars are usually sweet potato cellars. The area is small and there is not much food that can be stored. In contrast, the square wine cellar can be slightly larger and have a wider range of activities. Generally speaking, ladders are placed at the entrance of the cellar to facilitate access. The depth of the cellar is mostly more than two meters, which can play a good role in constant temperature. Pits will be covered with wooden boards or slates, and sometimes with a thick layer of straw. The temperature of the vegetable cellar is kept at about 0-5 degrees. Different kinds of vegetables are placed separately. Generally, potatoes, sweet potatoes and radishes are placed at the bottom, and cabbage is placed at the top of the shelf. Regular ventilation can last a long time. Large-scale food cellars are basically red bricks and equipped with lighting equipment.
Because of the thick dry soil in the north, the pit method is often used. Because of the weak thermal conductivity of soil, its temperature change is much smaller than that of the atmosphere. When it's too cold outside in winter, it helps to keep warm. In autumn or early winter, when the outside temperature is too high, the temperature in the cellar can still be kept low, and the humidity change in the soil is relatively stable, which is conducive to preventing fruit wilting. In addition, the gas exchange in the soil is poor, and the cellar is generally covered with plastic film, so the cellar has the natural coordination function of accumulating carbon dioxide and reducing oxygen, which can ensure that the food will not deteriorate for a long time! Low temperature has always been the king of fresh food, because bacteria have weak vitality and low reproductive ability at low temperature. Under the low temperature conditions of ice and snow in winter, heaven and earth are a big refrigerator, so there is no problem in natural preservation. It will be very cold deep underground in summer, so the ancients also hid food in deep non-concrete cellars to keep it fresh.