Seventeen strains in the fridge: how a culture library works

Buy a bag of plug spawn from us and you are not really buying a species, you are buying a strain. The distinction sounds academic, but it explains why one shiitake makes thick caps in the cold and another makes thin ones in warmth, even though both are "shiitake". Our nursery runs on seventeen such strains, each with its own documentation, and that library is the least visible and most decisive part of what we do.

What is a strain?

A strain is a specific genetic line within a species, comparable to an apple variety. Elstar and Granny Smith are both apples, but nobody confuses them. Mushrooms are the same: within the common oyster there are strains that fruit at ten degrees and strains that only start at twenty, strains with blue-grey caps and strains with brown ones, fast ones and slow ones. A strain originally comes from a single wild mushroom or one selected cross, and is then kept in culture by transferring it again and again. As long as that is done carefully, every plug stays genetically identical to the first.

Why does that matter for your harvest?

Because a strain is predictable and a species is not. Of a documented strain we know at which temperature it colonises, at which it fruits, how long it takes on a twenty centimetre log, which wood it prefers and what it will look like. That data sits on a sheet per strain, and that sheet is the basis of every instruction leaflet we send and every piece of advice we give. When we say the donko only makes thick caps in the cold, that is not hearsay, it is in its documentation. Without a strain, every piece of advice is a guess.

How do you keep a strain?

On agar, in petri dishes, in the fridge. Every strain lives as a white fan on a nutrient medium, and every strain has several dishes: a working copy we multiply from, and backup copies that are never touched. Cold pauses the mycelium without killing it, but not indefinitely. Every few months a strain is transferred to a fresh dish, and that is the moment things go wrong if you are not careful: a contamination, a labelling mistake, or slow weakening because a strain has been transferred too often. Managing a library is therefore mostly discipline: label, date, keep a logbook, and never work from the last copy.

What do we have?

Seventeen strains, twelve of which are in the shop: the common, pink and golden oyster, shiitake, lion's mane, maitake, reishi, nameko, pioppino, chestnut mushroom, wood ear and wine cap. The other five sit documented in the fridge and are not yet a product: king oyster, chaga, cordyceps, the brown button mushroom and the Sicilian oyster. Why not? Because having a strain is different from being able to make a product. King oyster is coming, that is a matter of time and testing. Cordyceps can be grown, but may not be sold as food in the EU; why is explained in a separate piece. And chaga is a story of its own: the fruiting body grows for ten years on a living birch, so what you can make from that strain is mycelium, not a mushroom.

Where does a strain come from?

Two routes. The first is buying from a professional culture bank, where strains have been selected and documented over years. That is where most of our library comes from, and the advantage is that every sheet is accurate. The second is isolating your own: a wild mushroom from the woods, a piece of tissue on agar, then months of testing whether it is worth keeping. That is the romantic part of the trade, and it rarely produces a strain better than what already exists. But sometimes it does, and we will write about that another time.

Why are we telling you this?

Because it explains the difference between a plug from a documented strain and a plug from "an oyster mushroom". Buy from us and you get the strain whose traits we know and whose instructions we wrote. That is no guarantee of a harvest, the weather and the wood have their say too. But it is the reason that when you ask about your log, we can tell you what is probably going on instead of guessing. The library is small, seventeen dishes in a fridge. Everything we sell starts there.