In Japan, there’s unique concept of keeping vegitables. It’s called “Etto Vegetables” / “越冬野菜” (“Overwinter vegetables” ). The concept is that vegetables are kept in the snow, or in the soil, or the storage where is cooled around 0 degree by snow during winter season. People used this concepts to keep vegetables as preserved food during winter.
In the book depicting the life of the snowy region of Japan in the Edo period, Etto vegetables was described in the story.(1) The book name is “Hokuetsu Seppu” published around 1840, So the concept of Etto vegetable has been existed in the old time.
In winter time, Inside of vegetable tends to be frozen and withered as temperature become less than 0 degrees. However, some vegetables have a mechanism to increase the sugar inside of their body water when they become around 0 degrees. (Low temperature saccharification)(1)
By increasing the sugar inside of their body water, the freezing point is lowered and the vegetables can be stored for a long time without freezing. In addition, it keep fresh and taste more sweet as water and sugar remain more because of saccharification effects.
To keep vegetables in the snow, radishes, carrots, potatoes, onions, green onions and cabbages are suitable. There are some brand Etto Vegetables in Japan too.
Etto vegetale brands in Japan:
Yukinaka Cabbage in Hokkaido
Vegetables sweeten under the snow in Yamagata (Radish, Spinach, Carrot, Apple, etc)
YukiShita Carrots in Niigata