1. What Is a Snow Room, and How Does It Keep Snow Until Summer?
A snow room is a structure where snow collected in winter is packed inside a building or enclosure. Even in summer, snow remains inside, cooling food with its chilled air. Materials from Joetsu City in Niigata Prefecture describe this as a technique that uses the properties of low temperature, constant temperature, and humidity to preserve and age agricultural products, rather than treating snow as a nuisance [2]. Before electric refrigerators became common, people used straw to pack snow around vegetables and fish, creating a natural fridge. In the Uonuma region, it is said that every household had one, storing daikon radishes and carrots. This is a local tradition in Uonuma, not a universal practice across Japan. In Shichikashuku Town, Miyagi Prefecture, a snow room keeps snow year-round, maintaining low temperatures and high humidity in summer without freezing in winter. This allows fresh storage of vegetables, fruits, rice, and buckwheat [3]. It is cold but not frozen. So, how cold and humid is it inside?
2. What Are the Temperature and Humidity Inside a Snow Room?
The Niigata Prefectural Agricultural Research Institute measured temperature and humidity in an ice-house-style snow room in Tsunan Town from November 2009 to April 2010. Inside the snow room, the average temperature was 2.7°C, with a high of 5.9°C and a low of 0.3°C. The average humidity was 96.9%. During the same period, potatoes in a refrigerator with a cover averaged 3.7°C [4]. The average temperature difference is about 1°C. Moreover, the snow room temperature fluctuated between 0.3°C and 5.9°C over six months; it was not always exactly 0°C. With humidity near 97%, the air is moist, making it harder for vegetables to wilt. If the average temperature difference is only about 1°C, items stored in a snow room and a fridge might seem similar. However, the same test showed a clear difference in potatoes.
3. Why Did Potatoes Get Sweeter in a Snow Room Despite Only a 1°C Difference?
When Kitakari potatoes were stored in a snow room, their sugars (glucose, fructose, sucrose) increased greatly from before storage, and more than in the refrigerator. Amino acid levels, however, showed no large difference between the snow room and the fridge [4]. In a summary from another year, sugar levels reached about 10 times the starting amount by the fifth month. Sprouts were not seen in the snow room until the fifth month, while they appeared in the fridge from the third month [1]. Again, this 10x figure is for sugar quantity, not perceived sweetness. Potatoes are known to increase sugar when kept cold. Materials from the National Agriculture and Food Research Organization show that making potato chips from potatoes with increased sugar from cold storage results in darker, unappealing colors [5]. Cold-induced sugar increase is not unique to snow rooms. In Shimane Prefecture, the leaves of a new vegetable called "Asukko" saw total sugar rise sharply from January, reaching about 7g per 100g in leaf stalks by February [6]. However, the materials used here do not fully explain why the difference between snow rooms and fridges occurred. So, does everything get sweeter in a snow room?
4. Which Foods, Such as Carrots and Pumpkins, Did Not Change in a Snow Room?
In the same Niigata Prefecture summary, carrots and pumpkins (Botchan variety) showed no difference in sugar or amino acids compared to refrigerated storage. Brown rice and miso stored for about 12 months were also equivalent to refrigerated storage. For carrots, the rate of damaged goods unsuitable for shipping was about 20% in the snow room and 40% in the fridge, roughly half [1]. This summary notes that results change greatly depending on variety, facility, and packaging. It is better not to generalize the potato results as "this is what happens in a snow room." Mold can occur due to high humidity, so caution is needed [4]. Other foods do change. In Fukushima Prefecture research, cabbage stored in a snow room for 2 weeks showed increased gamma-aminobutyric acid (GABA), a trend that lasted until 8 weeks. Winter cabbage in Aizu can be stored for 2 months after harvest in a simple snow room [7]. Some ingredients gain sugar, others gain components, and some stay the same. Reactions differ by food. Compared to vegetables, sake spends years in snow rooms.
5. How Does the Hakkaizan Snow Room Age Sake for 3 Years?
The "Hakkaizan Snow Room" at Hakka Brewing in Minamiuonuma City, Niigata Prefecture, uses 1,000 tons of snow. It is one of the largest in Japan for sake storage, keeping the interior always below 4°C using natural cold air [8]. 1,000 tons is equivalent to the weight of about 33,000 children weighing 30kg. The sake "Snow Room Storage 3-Year" is aged for 3 years in this room. What is clear is that the low temperature for long, slow aging is provided by snow’s cold. What other meanings does using snow’s coldness have besides taste?
6. How Much Electricity Does a Snow Room Save When Cooling Rice?
The snow room warehouse of JA Kitauonuma (Uonuma City) has been operating since August 2012. It stores about 1,500 tons of snow annually and cools 2 of 3 rice warehouses using snow’s cold heat. This reduces electricity consumption, with a calculated reduction of 78 tons of CO2 per year. The harvested Koshihikari rice is sold as snow-room-stored rice [9]. This 78-ton figure is an estimate, not a measured value. The snow room in Shichikashuku Town, Miyagi Prefecture, also uses less electricity than typical refrigeration facilities. Potatoes stored there are reported to have increased sugar content and are well-received [3]. Snowy regions use winter snow for both taste and electricity savings. The snow room is a tool specific to areas with heavy snow.
7. How Can You Compare Potatoes Stored at Home in Two Places?
Today’s activity: Choose two potatoes from the same bag. Place one in a dark, cool spot in the kitchen, and the other in the refrigerator’s vegetable compartment for 1-2 weeks. After taking them out, have an adult boil or steam them, and taste them side by side. Do not use sprouted or green potatoes, and do not eat them raw. Do not use frying for this comparison, as materials indicate that potatoes with increased sugar from low temperatures burn easily [5]. Your home fridge differs from a snow room in temperature, humidity, and duration, so results may not match the tests. Try to see if you can taste a difference. For further reading, the Niigata Prefecture research summary in Source [1] lists results for carrots, pumpkins, and miso. Reading about foods that "did not change" is an interesting entry point.