Fungi are largely employed as food in Southern Europe. They are eaten raw. They are also dried or preserved by cooking in vinegar, brine, or olive oil, which takes away the characteristic acrid taste of some of them. They are fairly rich in nitrogenous matter, but experimental observations have shown that this is imperfectly absorbed. They also contain fat, sugar (mannite and dextrose), fungic acid, and an acrid ingredient. They are used in this country chiefly for their flavour, and also for pickling and making ketchup.
A good brief description of the poisonous fungi is given by Knight as follows: -
Poisonous fungi are comparatively few, but as they closely resemble the edible forms, some distinctions must be observed. The common notion that poisonous fungi might be detected by discolouring a silver spoon, owing to the presence in them of sulphur compounds, is unreliable. The poisonous varieties are recognised generally by their high colour, scaly or spotted surface, and flesh either tough or watery. They usually grow in clusters upon wet or shady ground. On bruising they show a play of colours and yield a pungent milk, while their taste is bitter or burning the throat; on drying they become bluish. The poisonous matters in these belong to the class of narcotico-irritants, and cases of poisoning are best treated by the free use of emetics and castor oil. Edible fungi, on the other hand, are seldom high-coloured, scaly, or spotted, but are generally red or brownish. They break with a brittle fracture, retain their colour on drying, and grow best upon open, dry pastures. They have an agreeable smell and taste, but in some species any acrid taste may be dissipated by heat.
The chief edible fungi are the common mushroom generally used for making savouries and ketchup. The latter is made from the common mushroom by breaking it into small pieces and mixing with salt, which reduces it to an almost liquid state, then straining and boiling down to half the bulk. Spices of different kinds are added, and occasionally wine.
Iceland moss is a lichen found in Arctic regions. It contains 70 to 80 per cent, of a starch (lichenin) which is not very easily digested. Its nutritive value is therefore of a low order.
Irish or carrageen moss is a seaweed. The chief ingredients present is a vegetable jelly, the chemical composition of which is not fully known. It is specially noteworthy for the manufacture of a pleasant drink, made by adding cold water in the proportion of half an ounce of carrageen and 3 pints of water, then boiling and straining. It may be flavoured by spices if desired. If more carrageen is employed, the result is a mucilage which yields a jelly on boiling, which may be used as a nutritious and pleasant article of food which is fairly easily digested.