Japanese Dried Shiitake: Log-Grown Genboku and Shiitake Dashi
Dried shiitake, hoshi shiitake (干し椎茸), are a staple of Japanese cooking: soaked for a dark, savoury stock, then simmered until meaty. Many are grown on logs, genboku (原木), the traditional way.
This guide explains how log-grown shiitake are farmed, where Japan's dried shiitake come from, how Japan labels shiitake origin, and how to use them at home. It sits inside our Dashi Masterclass.
Our dried shiitake: Kōmi Japanese Dried Shiitake, 40g, log-grown in Japan and packed by Marutomo Bussan in Nakatsu, Ōita.
Log-Grown or Block-Grown?
Japan's Ministry of Agriculture (MAFF) describes three ways of growing mushrooms. Log growing (genboku) uses felled broadleaf logs such as kunugi and konara oak, outdoors or in simple shelters; shiitake and nameko are grown this way. Sawdust-block growing (kinshō) is done indoors, and is used for enoki, bunashimeji, maitake and eryngii. MAFF says log growing gives a flavour close to wild mushrooms, but depends on the weather.
The figures from Japan's Forestry Agency show the split. Dried shiitake are mainly log-grown outdoors: Japan produced 1,724 tonnes in 2025, up 9.5%, mainly in Ōita, Miyazaki and Kumamoto. Fresh shiitake were once mainly log-grown too, but in 2025, 95.1% of the 61,750 tonnes of fresh shiitake came from sawdust blocks, mainly in Tokushima, Fukushima and Iwate.
Source: MAFF and the Forestry Agency, special forest products production trends. Facts extracted and reworded.
How Log-Grown Shiitake Are Farmed
MAFF's aff magazine followed a grower in Shiiba, Miyazaki, from a family that has farmed there for about 200 years. Log growing takes more than two years:
- Kunugi oak is felled from late October to early November, when 30 to 70% of the leaves have turned, and left to dry for about a month.
- The logs are cut to about 110cm, drilled with 1cm holes, and plugged with shiitake spawn between January and early April.
- The logs are laid out to let the spawn run, for around 18 months. The spawn dies within about three hours if the log surface goes above 28°C, so shade matters.
- The next autumn the logs move to a shaded, rain-fed yard, the hodaba.
- Mushrooms come from mid to late October until about April, picked when the veil under the cap breaks.
Source: MAFF aff magazine, October 2021 mushroom feature. Facts extracted and reworded.
How Japan Labels Shiitake Origin
Since a change made on 30 March 2022, the origin of shiitake in Japan is the place where the spawn was put into the log or block, not where the mushrooms were picked. The Forestry Agency explains why: blocks inoculated abroad and fruited in Japan were being sold as Japanese, and shoppers could not tell the difference.
Source: Forestry Agency shiitake origin labelling Q&A. Facts extracted and reworded.
How to Use Dried Shiitake
- Rehydrate. Rinse briefly, as log-grown caps can carry bits of bark, then soak in cold water in the fridge for several hours or overnight. In a hurry, use warm water for about 30 minutes.
- Shiitake dashi. Keep and strain the soaking water: it is a dark, savoury stock. Dried shiitake are rich in guanylate, which works with the glutamate in kombu, so the two together make a deep dashi.
- Nimono. Simmer the soaked caps in dashi, soy sauce and mirin until glossy.
- Rice and noodles. Slice into takikomi gohan, udon or ramen.
See also our shiitake dashi masterclass.
Popular Products
Three to start with: the shiitake, the kombu to pair with them in dashi, and tamari for simmering.
Kōmi Ma Kombu, A Grade, 500g
Hokkaido kombu, the partner for shiitake in dashi. Also as 10-Year Aged White Bay, 500g.
Frequently Asked Questions
What does genboku mean?
Log-grown: shiitake grown on felled oak logs rather than sawdust blocks.
Where are Japan's dried shiitake grown?
Mainly in Ōita, Miyazaki and Kumamoto, on Kyushu.
How long should I soak dried shiitake?
Several hours or overnight in cold water in the fridge; about 30 minutes in warm water if you are short of time.
Can I use the soaking water?
Yes. Strain it and use it as stock.
How is shiitake origin labelled in Japan?
By where the spawn was inoculated, under a rule changed in March 2022.
Where to Buy Dried Shiitake in the UK
Our dried shiitake are Kōmi Japanese Dried Shiitake, 40g: log-grown in Japan and packed by Marutomo Bussan in Nakatsu, Ōita.
For more, browse the Dashi Masterclass. Read next: Hatcho miso guide · Udon guide
Sources: Ministry of Agriculture, Forestry and Fisheries of Japan and the Forestry Agency: special forest products production trends; aff magazine October 2021 mushroom feature; shiitake origin labelling Q&A; retrieved 5 November 2026; Kōmi product specification. Facts extracted and reworded, not reproduced.
