Pins, Flushes, and Harvest

From threads to pins

The casing layer is on, damp and cosy. Now the waiting begins. Inside the casing, the mushroom's threads bundle together into thicker cords called rhizomorphs (say RY-zoh-morfs), a bit like tiny ropes. These ropes are the launch pads for mushrooms.

Then the farmer changes the air. Fresh air is blown into the room to lower the amount of carbon dioxide — the gas we all breathe out. Lots of carbon dioxide tells the mycelium to keep growing threads. Clearing it away sends a new message: make mushrooms now.

Soon tiny white bumps appear on the casing, no bigger than a pinhead. These are pins — baby mushrooms. This stage is called pinning, and it is one of the most exciting things to watch.

Flushes of mushrooms

The pins swell quickly, day by day, into full mushrooms. They do not all come at once. They arrive in waves called flushes.

A farm picks each flush over a few days, then the block rests and drinks up water for about a week. Then another flush of pins appears, and another. A single block of compost can give several flushes before it is finally used up. Harvest usually starts around 15 to 21 days after the casing goes on.

Picking at the right moment

Here is where you decide what kind of mushroom you get. Because the button, cremini, and portobello are all one species, the picking time chooses which one you harvest.

• Pick early, while the cap is closed and the gills are hidden underneath, and you get a firm white button.

• Wait a bit longer and the browner ones become cremini.

• Leave them longest and the caps open out wide and flat, the gills turn dark brown, and you have a big portobello.

To harvest, you gently twist and lift each mushroom from the casing rather than yanking it, so the block stays healthy for the next flush.

Clean hands, and always cook

Growing food means being careful and clean. Wash your hands before and after handling mushrooms, and brush off any bits of casing.

And remember the golden kitchen rule: button and portobello mushrooms are cooked with an adult before eating — never eaten raw. Cooking makes them tastier and gentler on your tummy. Sliced buttons in a pan, or a whole portobello baked in the oven by a grown-up, are both delicious.