of the genus Saccharomyces are truly one of nature's
bounties. These are the yeasts that make dough rise by releasing
carbon dioxide gas when they break down certain sugars. This
process, called fermentation, gives bread its wonderful texture
and delicious flavour. The recipe is simple. Mix a little yeast
with sugar and water, and add it to dough made from flour. Keep
it warm and watch it rise.
The endpoint of respiration is carbon dioxide and water. But with incomplete respiration ethyl alcohol is produced as an intermediate by-product. Add yeast to a sugary liquid and it will ferment the sugars to produce wines, beers, and other beverages that are enjoyed in many cultures.
Wine is simply fermented grape juice. Wild yeasts are usually present on the skins of grapes used in winemaking, but they can only tolerate low levels of alcohol. Over many generations, winemakers have selected special yeasts that can survive in alcohol concentrations up to about 12 percent. Different yeast strains also impart distinctive flavours to the wines. Beer is made by the fermenting action of yeast on malt (the sugary product of germinated barley grains) and other sugars.
Asian rice wine, or Sake, is another product of yeast fermentation,
but it also requires the services of another fungus. Unlike
grape juice, which contains sugars, rice contains starch. The
fungus Aspergillus oryzae is added to break down the
starch to glucose, a simple sugar, that can be fermented by
Many foods owe their flavour to the work of moulds. Cheeses such as Danish blue, Roquefort, and Brie are ripened by moulds. Moulds are also used in the processing of soy sauce, miso, and other Asian delicacies.
Mushrooms have been a source of food for centuries, and are relished in dishes such as omelettes or sushi. In continental Europe and parts of Asia (and more and more nowadays in North America) people harvest many species of edible wild mushrooms. Luckily for us, some are fairly easy to cultivate.
The so-called 'commercial' mushroom, Agaricus bisporus,
has been farmed in North America since the 1880s. It is grown
on a specially-composted mixture of animal manure and straw,
under carefully controlled conditions. Buttons, cups or flats
are all available for purchase. These are different stages in
the development of the mushroom. Buttons are preferred by sellers
as they have a longer shelf life. Buyers may prefer the cup-shaped
stage, particularly for stuffing, while the flat caps have a
stronger flavour. The shelf life of the expanded flat is a mere
24 hours, after which time their appearance quickly deteriorates.
The delicious cremini and portobello mushrooms we now see in
supermarkets are different strain selections of A. bisporus.
Not only do fleshy mushrooms taste good, some have long been used in traditional Chinese medicine, with alleged therapeutic effects against high blood pressure and some cancers. Shiitake mushrooms contain at least two efficacious compounds that seem to boost the human immune system . Reishi mushrooms may also have medicinal properties, but they are less well understood by scientists in the west.
Western medicine has harnessed some microfungi to great purpose.
One of the miraculous moulds is Penicillium notatum.
Its power to kill bacteria was discovered accidentally by Alexander
Fleming in 1928 in London. The antibiotic penicillin, produced
by P. notatum, changed the face of medicine. It has saved
the lives of many and relieved the suffering of millions.
Many wonder drugs have since been derived from fungi. They include other antibiotics, such as griseofulvin (used to treat fungal disease of the skin), and the cyclosporins (used as an anti-infection drug for transplant patients and diabetics).
Fungi's ability to kill insect pests and weeds offers an environment-friendly
alternative to pesticides. The use of one natural organism to
attack another is called
biological control, or biocontrol.
Fungi have proved effective against Gypsy Moth, Colorado Potato
Beetle, aphids, whitefly, and mosquito larvae, to name a few.
Fungal agents have also controlled weeds including Vetch, Dodder,
Bindweed, and Thistle. Some fungi can even control other troublesome