Mushroom broth from stems and trimmings: throw nothing away

Anyone who grows their own throws away more than they realise. The tough base where a fan of oyster mushrooms sat on the block, the woody stems of shiitake, the frayed edges of a specimen left a day too long. Together that is easily a third of the harvest. That part is too chewy to fry, but it is full of exactly the flavour compounds you want in a broth. This is how to waste none of it.

What do you keep?

Anything that is mushroom and not going in the pan. Shiitake stems are the most valuable, packed with flavour and useless fresh. The bases of oyster mushrooms, the hard core of a lion's mane, the thick stem of a wine cap, cap trimmings. Mushrooms slightly past their best, with edges curled upward, can go in too. Collect it all in a tub in the freezer; when it is full, it is broth day. Freezing is a bonus, by the way: cell walls break and the flavour releases more easily.

What stays out?

Substrate. Trim the base cleanly away from the bit of straw or sawdust sometimes still attached. Also no mouldy pieces, no slimy remains and no mushrooms that smell of ammonia; those belong in the bin, see the smell piece. Broth is not a way to rescue spoiled things, it is a way to use tough ones.

The method

No quantities, because they do not matter. A pan, the frozen trimmings, and cold water to cover them generously. Optional additions: an onion quartered with the skin on, a carrot, a stick of celery, a bay leaf, a few peppercorns. No salt, that comes later with the dish. Bring to the boil, then turn the heat down until it barely moves, and let it draw for one to two hours without a lid. Strain through a fine sieve or cloth, press out the solids, done. The broth is brown, clear and smells of the forest.

Why cold water and gentle heat?

Hard boiling makes broth cloudy and bland, because the flavour compounds cling to the foam. Slow drawing pulls the glutamates out of the mushroom tissue, and those are why this broth tastes so savoury without any meat. The same principle as Japanese dashi made with dried shiitake, only with your own trimmings.

Even better with dried

If you have dried shiitake in the house, add a cap or two. Dried brings the smoky depth fresh does not have, and together with the fresh trimmings the broth is more complete than with either alone. The soaking water from dried shiitake is broth in its own right, by the way; always pour it in rather than down the sink.

Storing

Three days in the fridge, months in the freezer. Ice cube trays are handy: one or two cubes are exactly the umami boost for a risotto, a sauce or a pan of mince. Reduce the broth further to a syrupy glaze and you have a concentrate where a tablespoon does more for a dish than a whole cube from the shop.

This is the part of growing nobody writes about: what happens after the pretty photos are taken. A grower who eats everything, stems included, simply gets more out of a block or log than one who only counts the caps.