The final yield will be around 750 g stock.
Ingredients for Mushroom stock.
100g unsalted butter
750g button mushrooms, halved
200g Dry Madeira
8 sprigs of thyme
5g black peppercorns
1500g spring water
How to make Mushroom stock:
To clean the mushroms I put them all in the sink filled with water, then clean them one by one with papertowels, brushing off the dirt. Once cleaned place in a bowl, when the bowl is full place your hand on top and tip over to drain off any water, then place the mushrooms on a plate topped with kitchentowels to drain further. Once kinda dry, half all mushrooms with a knife.
Melt the butter in a pressure cooker over medium heat. Add the mushrooms and stir and shake the pot to coat them with the melted butter. Raise the heat to medium-high and continue to cook until the mushrooms are golden brown. The mushrooms will release loads of water but continue to cook until the water is evaporated. When evaporated the mushrooms will brown quite quickly so keep a close eye on them so they don’t go too far.
Deglaze the pan with the Madeira. Once it’s boiling set fire to the alcohol with a match or lighter while standing well back. Once the flames subside let it boil down to a thick syrup.
Add 1500g spring water, the black peppercorns and the thyme to the pressure cooker, put the lid on. Bring up to full pressure over high heat then reduce the heat to low and cook for 30 minutes.
Take the pressure cooker off the heat and allow to cool. Once the pressure dissipated remove the lid and strain the stock into a clean saucepan through a chinois. Reduce the stock by half over high heat.
This reduction is easily done by first weighing the empty saucepan, then weighing the saucepan with the sieved stock in it. Then take this total weight minus the empty saucepan weight, divide by two and add to the empty saucepan weight. This is the final weight we are aiming for when the stock is reduced by half. Keep weighing your saucepan while reducing until this weight is hit.
Pass the stock through a SuperBag or a sieve lined with two layers of wet muslin cloth. Portion then refrigerate or freeze for later use.