The enthusiasm is great during the walk in the forest: numerous porcini mushrooms stand on a mossy clearing overgrown with spruce trees. However, the joy is clouded when cutting it off, because the interfaces turn blue. Is it a toxic double?
If the mushroom turns blue when pressed, it is not a porcini mushroom
Porcini mushrooms do not discolour
In fact, porcini mushrooms do not discolor either when cut or when pressure is applied to the whitish to yellowish-green tubes. If, on the other hand, the tubes and interfaces immediately turn blue when touched, it is most likely the chestnut boletus, which is also edible and very similar to the porcini mushroom. The blue color reaction comes from the conversion of yellow dyes to blue by exposure to atmospheric oxygen. You'll also find the same reaction in Flake-stemmed Witch Boletus and Red-Footed Boletus, both of which are also edible.
chestnut boletus
In deciduous forests, especially in coniferous forests under spruce, the chestnut boletus is common. It is often accompanied by wild blueberries. In contrast to the finely moistened stalk of the porcini mushroom, that of the chestnut boletus has brownish longitudinal fibers. But be careful: This fungus stores toxic heavy metals such as radioactive cesium in its brown cap skin. You should therefore not eat the mushroom too often, especially in southern Germany.
Flake-stemmed witch boletus
With its name and the typical red-colored tubes, this mushroom signals a toxicity that it does not have. Instead, it is an excellent edible mushroom that is even superior to the porcini mushroom in some respects: the flake-stemmed witch's boletus is rarely attacked by maggots. Similar to the porcini mushroom, it prefers beech and spruce, but grows almost exclusively on poor, sandy soil. Mosses and blueberry weed are reliable indicators of such soil conditions.
Red-footed boletus
The red-footed boletus is a tasty mushroom found in abundance in many deciduous forests well into late fall. However, you should only take young specimens with you, as the older ones are often affected by the poisonous golden mold. You can recognize the infestation by the fact that the yellow tubes or the cap are covered with a velvety, whitish to yellow layer of mold.
Risk of confusion with the gall boletus
The gall boletus is also very similar to the porcini mushroom, which is not poisonous but very bitter. The porcini mushroom has a whitish mesh, especially at the top of the stalk, and the gall boletus has a brown one. If in doubt, you can carefully cut into the found mushroom with a knife and lick it with your tongue: The non-poisonous bile boletus lives up to its name - it tastes like bitter bile!
tips
When picking mushrooms, remember that you are only allowed to take small amounts out of the forest for your own use.