Drying shiitake: why dried is sometimes tastier than fresh

October brings our biggest shiitake harvest of the year from the logs, and it is too much to eat fresh. That is not a problem but an opportunity, because shiitake is one of the few mushrooms that improves with drying. Japanese cooks pay more for dried shiitake than for fresh, and they have a good reason. Here is how it works, and how to do it at home.

Why does shiitake taste better dried?

Two things happen during drying. The water disappears, leaving all the flavour compounds concentrated. And, more importantly, drying creates a compound that fresh shiitake barely contains: lenthionine, responsible for that deep, smoky, almost meaty aroma of dried shiitake. On top of that, glutamates rise, the umami taste. A dried shiitake is therefore not a preserved fresh one, it is a different product with its own flavour. For broth, ramen and stews, dried is the better choice; for a quick fry, fresh tastes better.

Which shiitake do you dry?

All of them, but thick caps are more rewarding. A thick donko cap stays meaty after drying and comes back almost as firm as fresh after soaking. Thin caps dry into crisp chips mainly suited to grinding into powder or dropping straight into a soup. Remove the stems (keep them, they make broth) and slice large caps if you like. Do not wash, just wipe.

Drying in the oven

The fastest way. Lay the caps gills up on a rack, not a baking tray, so air can pass underneath. Oven at 50 to 60 degrees, fan setting if you have it, and the door propped ajar with a wooden spoon so the moisture can escape. After four to eight hours they are done: hard, dry and light, and they snap when bent. If a cap still bends, there is moisture left and it will go mouldy in the jar.

Drying without an oven

The radiator works fine in winter: a rack or piece of mesh on the radiator, caps on top, two to four days. A food dehydrator is the luxury version and runs at the same temperature as the oven. Threading them on a string, as in old photos from Japan and Italy, works too, but only in a dry, airy room; in a north-west European kitchen in November they go mouldy before they dry.

The sunlight trick

Shiitake contains ergosterol, and ergosterol converts to vitamin D2 under UV light. That still works after harvest. Before drying, or just after, lay the caps in full sun for a few hours with the gills facing up. The vitamin D content climbs to levels no supplement can match. It costs nothing, and it is why commercial growers sometimes give their dried shiitake extra UV. Cloudy weather works less well, but a clear autumn afternoon is enough.

Storing and using

Fully dry, in a well-sealed jar, in a dark place. They keep for a year, and really longer. To use, soak for twenty minutes to an hour in lukewarm water; the soaking water is pure broth, never throw it away. For a quick umami boost, grind a handful of dried caps to powder in a coffee grinder: a teaspoon through a sauce, soup or minced meat does what a stock cube promises and rarely delivers. How to make and use that powder follows later in a separate piece.

Anyone with a donko log harvesting thick, cracked caps in the cold months has, with this, the best the species offers: a winter's worth of dried shiitake from their own wood.