Arafune-Azumaya Cold Storage Facilities
Natural wind caves used to refrigerate silkworm eggs for increased silk production.
The Arafune-Azumaya Cold Storage Facilities are natural refrigerators that supported silkworm production linked to the Tomioka Silk Mill. Located in the towns of Shimonita and Nakanojō, Gunma Prefecture, Japan, they hold joint status as a National Historic Site and, along with the Tomioka Silk Mill, are part of the UNESCO World Heritage serial nomination "Tomioka Silk Mill and Related Sites." These structures were adapted wind caves that maintained steady cold temperatures for preserving silkworm eggs, which allowed farmers to boost output of raw silk cocoons to satisfy demand.
After the Meiji restoration, the new government needed export income to fund industrialization and westernization. Products already made in Japan that could be sold abroad at good profit included tea, silk thread, and silkworm cocoons. Due to the pébrine disease affecting silkworms in France and Italy, plus instability from the Taiping Rebellion in China, Japanese silk became highly sought after. In 1862, just before the restoration, raw silk and silkworm cocoons made up 86% of Japan’s exports. But soon after, overproduction and the recovery of European and Chinese silk regions caused raw silk prices to drop sharply. The Meiji government responded by shifting focus to higher-value silk goods like thread and cloth. The opening of the Tomioka Silk Mill in 1872 sparked a sericulture boom in Gunma Prefecture and nearby areas, and raising silkworms became the main work for many farmers.
To control when silkworms hatched, several wind caves were turned into natural refrigerators for cold storage of silkworm eggs. Cool air forms when wind passes through rock crevices filled with snow that accumulates over winter. Even in summer, when outside temperatures exceed 20 degrees Celsius, the cave interior stays a constant few degrees above freezing. This allowed farmers to increase the number of silkworm harvests per year from one to two or even three, greatly boosting raw silk cocoon production to meet rising demand. When government oversight of the silkworm industry ended in 1917, 239 such facilities were recorded across Japan. They remained in use into the mid-twentieth century, until mechanical refrigeration made them obsolete, and most have since vanished or their exact locations are unknown.
The Arafune facility in Shimonita sits on a slope beside a stream at about 840 meters elevation, ne
- location
- Shimonita and Nakanojō, Gunma Prefecture, Japan
- type
- Natural refrigerators (wind caves) for silkworm egg storage
- period_of_use
- Late 19th to mid-20th century
- peak_number
- 239 facilities confirmed nationwide in 1917
- capacity
- Arafune facility could store 1.1 million silkworm eggs; Azumaya facility could store over 100,000 trays
- designation
- National Historic Site and UNESCO World Heritage Site (part of serial nomination)
- associated_site
- Tomioka Silk Mill
Lore & Background
The Arafune facility in Shimonita, built from 1905 to 1912, consists of three large wind caves with the largest storage capacity in Japan. The No. 1 cave had a frontage of 7 meters and depth of 3.5 meters; No. 2 had 11.5 by 3.5 meters; No. 3 had 8 by 3.5 meters. Storehouses above were three-story structures with clay-covered walls. No buildings remain, but masonry is intact, and cold air continues to blow out at around 2°C year-round. The Azumaya facility in Nakanojō, built in 1906, was one of the largest regional wind caves, with a management building and two storages; its No. 1 wind cave was on the second basement floor. Only masonry and the office cornerstone remain.
Reader's Guide
The Arafune-Azumaya Cold Storage Facilities represent a key innovation in Japan's Meiji-era sericulture industry. By using natural wind caves to refrigerate silkworm eggs, they enabled multiple silkworm crops per year, dramatically increasing raw silk production to meet global demand. This supported Japan's industrialization by providing a valuable export product. Their designation as a National Historic Site and inclusion in the UNESCO World Heritage listing 'Tomioka Silk Mill and Related Sites' underscores their historical importance. The facilities illustrate how traditional knowledge of local geography was harnessed for industrial purposes before modern refrigeration. Today, the surviving masonry and constant cold air serve as tangible reminders of this once-widespread practice. Their preservation offers insight into the technological and economic strategies that helped Japan modernize. The sites also highlight the decline of such methods as mechanical refrigeration spread in the mid-20th century, leading to the disappearance of most similar facilities nationwide.
Did You Know?
- The Arafune facility could store 1.1 million silkworm eggs, the largest capacity in Japan.
- Even in summer, the caves maintain a constant temperature of around 2°C year-round.
- When government control ended in 1917, 239 such facilities were confirmed nationwide.
- The Azumaya facility was built in 1906 and could store over 100,000 trays of silkworm eggs.
Frequently Asked Questions
What are the Arafune-Azumaya Cold Storage Facilities?
They are a pair of natural wind caves in Gunma Prefecture that were repurposed as cold-storage chambers for silkworm eggs during the late 19th and early 20th centuries. The steady subterranean temperatures kept the eggs viable, enabling local farmers to produce more raw silk cocoons to feed the Tomioka Silk Mill.
Where exactly are the Arafune and Azumaya facilities located?
The two sites sit in the towns of Shimonita and Nakanojō, both in Gunma Prefecture on central Honshu, Japan. They carry a joint National Historic Site designation and form part of the UNESCO serial listing titled "Tomioka Silk Mill and Related Sites."
How did natural wind caves function as refrigerators for silkworm eggs?
The caves exploited natural airflow through rock formations to maintain a consistently cool temperature year-round, which is exactly what silkworm eggs need to remain dormant and healthy. By housing the eggs in these caves, producers could time hatching to the silk-rearing season and dramatically boost cocoon output.
How many silkworm eggs could the Arafune and Azumaya facilities store?
At peak capacity the Arafune cave held roughly 1.1 million silkworm eggs, while the Azumaya cave stored more than 100,000 trays. Nationally, 239 similar wind-cave refrigerators were documented by 1917, making these two among the best-preserved surviving examples.
Why did UNESCO include them in a World Heritage nomination?
They are recognized because they represent a distinctive pre-industrial technology—using geology itself as a cooling system—that was essential to Japan's early silk industry. Together with the Tomioka Silk Mill, they illustrate the full chain from egg preservation to silk production that made Meiji-era Japan a major global silk exporter.
More in World Heritage Sites in Japan 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record