For centuries, edible mushrooms defied cultivation and it wasn’t until the 1650s that they started to be farmed on the outskirts of Paris in limestone caves.
The caves provided the ideal growing conditions, of darkness, wet and cold. Today’s mushroom growers employ more high-tech science in the cultivation of this most fascinating of crops, but the magic and mystery still remains. Mushrooms are nurtured through a six to eight week cycle in computer-controlled rooms with mushroom beds layered like ship’s bunks.
Mushrooms are not a vegetable, but the fruiting body of a fungi and start out life as microscopic spores (just one mature mushroom can produce 146 million spores). They are so tiny that they are not visible to the naked eye, necessitating delivery to the grower in bags of spore coated rye grain.
The grain is scattered into pasteurised wheat compost and subjected to different levels of temperature and humidity until it germinates to produce a tube. This tube branches into a mass of threads to produce a mycelium, which finally “fruits” to produce the mushroom. These young mushrooms are called pinheads.
People often ask why it is that mushrooms are not seen growing in a field for many years and then, one spring or autumn, a crop suddenly appears. The explanation is that mushroom mycelium can lie dormant for years and only when conditions are right will mushrooms grow. The term “cultivated” mushroom does not mean that the mushroom is a forced, unnatural growth. The grower aims to produce exactly the same conditions that nature provides at certain times of the year, all year, conditions that stimulate the mycelium from its dormant, vegetative state to a reproductive state. Once the mushroom has been formed, the grower will maintain an environment with temperatures of 17-18C and a humidity range of 85%-90% which are ideal for the mushroom to grow.
Mushrooms grow in bursts, known as flushes. Most of the crop is picked in the first three weeks, but the flushes can keep appearing for up to six weeks.
The white and brown mushroom (Agaricus bisporus), is picked at four different stages of growth – button mushroom (first stage), closed cup mushroom (second phase), open cup mushrooms (third stage) and large flat mushrooms (fourth stage). A button mushroom, if not picked, will double in size every 24 hours.
The mushrooms are all harvested by hand and can be packed and on the supermarket shelf from within 24 hours. Picking is a very skilled job as the delicate mushrooms can bruise very easily.
The mushroom industry is the ultimate recycler, using waste wheat straw for the compost and then returning everything to the land - either to arable farms or to garden centres.
Mushrooms are unique among the other fruit and vegetables in the supermarket in that they can be grown in totally controlled conditions, not dependent on seasons, and can therefore be made available all year round.
Other mushrooms which are commonly cultivated for the UK market include oyster, shiitake, Enoki and Shimeji mushrooms - which are grown using different cultivation methods to the white and brown mushrooms mentioned above. Click here to learn how they are cultivated.