How a plug is made: from petri dish to colonised dowel

Open a bag of plug spawn and you see wooden dowels with some white fuzz on them. Not spectacular, until you realise every dowel is a living colony that started months earlier on a petri dish. This is the story of that journey, because once you understand how a plug comes to be, you also understand why it does what it does in your log.

Step 1: it starts on agar

Every species in our range lives as a strain in our archive: a documented culture with known traits, from flavour to growth speed. We keep such a culture on agar, a nutrient medium in a petri dish. There the mycelium grows as a white fan, and that fan tells you the health of the strain at a glance: an even, vigorous fan is good news, spots or colour differences mean intervening.

This is also where most of the care goes. A culture that is not right at this stage only gets worse further down the line. Multiplying starts only when the foundation is sound.

Step 2: from agar to grain

From the dish, the mycelium moves onto sterilised grain. Grain kernels are full of moisture and nutrition, so the mycelium grows much faster on them than on agar. After a while every kernel is a white ball of mycelium, and the kernels roll loosely apart. That is exactly the point: grain spawn can be scattered, which makes it the perfect stepping stone for inoculating bigger volumes.

Sterility is everything at this stage. Grain is not picky about who grows on it, and a single mould spore from the air is enough to lose a whole jar. So this work happens with sterilised material, in clean air, with more alcohol on our hands than at the pub.

Step 3: the dowels

The dowels themselves are hardwood, 8 millimetres thick and 35 millimetres long, with a ribbed profile. That profile is not a detail: the grooves increase the surface area, giving the mycelium more grip and, later in the log, faster contact with the surrounding wood.

Before any mycelium joins, the dowels are soaked and sterilised. Dry hardwood is uninhabitable, mycelium wants moist wood. Then the dowels go into bags together with grain spawn, and the waiting begins.

Step 4: weeks of colonising

In the incubation room, dark and around room temperature, the mycelium creeps from the grain into the dowels. First the grooves turn white, then it moves into the wood fibre itself. After several weeks to a few months, depending on the species, every dowel is colonised through and through. A slow species like reishi takes its time, an oyster mushroom races through.

Colonised does not mean the plug has to look snow white, by the way. The mycelium sits mostly in the wood, not on it. A plug with a modest white haze can be fully occupied inside.

Step 5: checks and cooling

Before packing comes the check: smell (fresh, like forest floor), colour (white, no green or black) and colonisation. Then the plugs go into cold storage. Cold pauses the mycelium without harming it, just like winter does outdoors. That keeps a plug at full strength for months, until it disappears into a freshly drilled hole at your place and wakes up there.

Why this story predicts your harvest

Everything the plug will do in your log is a repeat of this journey: establish, expand, conquer. A plug from a healthy culture, fully colonised, has the routine built in. Which is why we dare to say: when something goes wrong with a log, it is almost never the plug, and almost always the wood, the timing or the moisture. We wrote about those three earlier, and there is much more to come.