Behind the Rise of Wood Ear Mushroom Cultivation at Mainichi Printing Plant

Unexpected Places Yield Unique Story Ideas

Sometimes, the most intriguing story ideas come from the most unexpected places. In recent years, as Japan experiences increasingly severe weather patterns—ranging from intense heatwaves to heavy tropical rains—indoor plant factories have emerged as a promising solution. These facilities, which are not affected by external weather conditions, are gaining significant attention. More companies are now setting up cultivation spaces within buildings and factories, where temperature and humidity can be precisely controlled.

While searching for potential interview subjects, I stumbled upon an unusual yet fascinating development at a Mainichi Shimbun printing plant. This facility, located in Kawaguchi, Saitama Prefecture, is one of the key sites responsible for printing not only the Mainichi Shimbun but also other daily newspapers and municipal newsletters. Within this industrial setting, there's a peculiar and expansive space that resembles a laboratory, tucked away in one corner.

As Yukio Taku, the 49-year-old printing department manager, invited me to "go inside," I was met with a scene that defied expectations. The room was filled with densely packed mushroom beds, some of which had already grown impressive black mushrooms. This area is dedicated to cultivating wood ear mushrooms, a popular ingredient in Chinese cuisine. The cultivation room was completed in February, and shipments began in March.

Why Grow Mushrooms in a Printing Plant?

The decision to grow mushrooms in a printing plant stems from the challenges faced by the print news media. With declining newspaper circulation, companies in the sector are constantly seeking ways to make effective use of their existing facilities and employees. Printing plants maintain strict control over temperature and humidity to ensure the quality of printed materials. It was Taku who first proposed utilizing this environment for growing wood ear mushrooms.

Currently, 90% of the wood ear mushrooms distributed domestically are dried imports from China. Taku saw an opportunity to create a local alternative. However, mushroom cultivation requires a consistent supply of water. To start trial cultivation, a small greenhouse was placed in an above-ground household pool.

The newspaper printing plant operates 24 hours a day. Taku and his colleagues took turns watering the mushrooms every four hours, both day and night, while carefully monitoring temperature, humidity, and carbon dioxide levels to determine the optimal growing conditions. This knowledge was then applied to the design of the cultivation room.

A Growing Business

Employees now take turns harvesting mushrooms between their regular printing tasks, and the facility ships approximately 40 kilograms of mushrooms daily, both fresh and dried. The mushrooms, protected by the dual environments of the factory and the cultivation room, are thick and can be shipped year-round. Their high quality has even attracted inquiries from prestigious establishments such as Hotel Chinzanso Tokyo, Chinese restaurants Kamonka and Choryumon, and the upscale supermarket Kinokuniya.

Taku's ambitions are expanding. He envisions using the company's newspaper distribution network and sales outlets to deliver mushrooms directly to readers. "Could we deliver mushrooms to readers using our newspaper distribution network and sales outlets?" he asks. The idea is bold, but it could become a new selling point for the company.