One of the specialist industries around Saumur is the growing of comestible mushrooms. The deep caves in the soft rock make for ideal growing conditions with constant temperature and humidity. We visited such a farm while we were there.
The mushrooms are grown for the most part, in small bales of nutrient wrapped in black plastic and with holes cut in, through which the fruiting bodies of the mushrooms grow. Different recipes of nutrient suit different species of mushrooms, but most seem to be based on straw or hay, with manure added.
The place we went to is called Le Saut aux Loups and claims some 3km of caves under exploitation, of which about 500m are open to visitors. The displays showed not only current crops of growing mushrooms, but also how they were grown in the past. Apparently, they used to use internal combustion engines for certain mechanical tasks in the caves. Despite the (natural) ventilation in place, I bet it made for a nasty working environment.
Gathering wild mushrooms is fairly popular in France, and every year some 1,000 people are poisoned, of which about 2% die. The most common cause of death being the Death Cap fungus that resembles a number of edible species. About the same number of people are accidentally shot and killed while hunting.
I have been out on a mushroom gathering in an organised group along with an expert, and have also eaten some normal "champignons de Paris" (the small white ones with pink gills that you find in supermarkets everywhere) that I found in the garden.
It's not something I do very often.