Grains from grasses provide most of the world's food supply for humans. But in most cases, we do not eat these grains directly as they are produced by the plants. Instead, we use them as a source of starch. To make the starch more pleasing and digestible for human consumption, we usually convert it to more complex and tasty forms of food and drink, often with the help of fungi.

Fungi is the plural word for "fungus". A fungus is a eukaryotic organism. Yeasts, moulds and mushrooms are examples of fungi. The study of fungi is called mycology. Like animals, humans and most bacteria, all fungi are heterotrophs. This means that they get their energy by eating organic substances. In contrast, plants get their energy directly from light and for this reason plants are called autotrophs. Although fungi have much more in common with animals than plants, mycology is often seen as a branch of botany.

Most fungi are large enough to be seen with the eye. However, some are microscopic organisms and the study of microscopic fungi is encompassed by the field of microbiology. Some microscopic fungi, for example yeast, are used in the food and drink industry to produce bread, beer and wine. Other fungi are important in the pharmaceutical and biotechnology industries and are used in the production of antibiotics and various enzymes.

Although the use of fungi as a component in the food making process is more common now than in the recent past, these food products, with some notable exceptions, are still not a familiar sight to western cultures. The use of the term food-making process is used here to mean those food products that require the aide of fungi in their production. For example, the one with which you are most familiar is baked bread. The yeast is utilized in making the dough rise so that bread will come out light and fluffy. Without yeast, bread would be much denser and harder. Blue cheese would be another examples. Asian cultures, however, have a large varieties of such food, some of which have become well known in this country. This is possibly because larger number of Americans have become more adventurous in their dietary habits that has led to these types of food becoming more common place in our society. This is particularly true, in Hawai‘i, where there is a large Asian population. I have excluded mushrooms from such foods since they are the actual food product rather than being utilized to create another food product. We will cover some examples of such products and discuss the processes by which fungi are integrated into their production.

Baker’s (or brewer's) yeast (Saccharomyces cerevisiae) converts the starch from grain into ethanol. This process also forms carbon dioxide bubbles in bread dough, causing it to rise, which gives baked bread its light texture. The ethanol and carbon dioxide are baked away in bread making (which produces the pleasant aroma of baking bread). In contrast, the ethanol and carbon dioxide are retained when yeast is used to ferment grain into beer. The carbon dioxide gives beer its fizz, and the alcohol and yeast contribute to the taste and appeal of beer to those who enjoy it. Sugars, especially from fruit such as grapes, are also converted into alcohol and carbon dioxide by yeasts in the production of wine (although the carbon dioxide is not retained in most finished wine, as it is in beer). Many different strains of S. cerevisiae are used in wine production, which contributes to the distinctive nature of wine from different regions and wineries. Many other species of local, native yeasts are also used in producing distinctive local wines and beers. For example, fission yeast (Schizosaccharomyces pombe) was first isolated from African millet beer. Fission yeast takes its specific name (pombe) from the Swahili word for beer.

Brown molds of the genus Aspergillus are important in some human diets. Aspergillus tamarii acts on soybeans in the production of soy sauce, and A. oryzae is used in brewing the Japanese alcoholic beverage sake from rice. Aspergillus niger is the source of most commercial citric acid production. Citric acid gives food and soft drinks a tart taste and is also used as a food preservative. But some species of Aspergillus that grow on grains and on nuts such as peanuts and pecans produce extremely carcinogenic (cancer- inducing) compounds called aflatoxins. Aflatoxins can occur in high concentrations in foods such as peanut butter. In the United States and most other industrialized countries, moldy grain infected with Aspergillus is typically thrown out. In Africa, where food is scarcer, the grain is often eaten, moldy or not, and causes severe health problems, including high levels of certain cancers.

Penicillium is a genus of green molds, of which some species produce the antibiotic penicillin, as described in the beginning of this chapter. But several species of Penicillium are important for food production as well. For example, P. camembertii and P. roqueforti are the organisms responsible for the characteristic strong flavors of Camembert and Roquefort cheeses, respectively.

Many fungi serve directly as a human food source. Mushroom enthusiasts seek out the delicious fruiting structures of a wide variety of edible sac and club fungi. In the United States, relatively few species of mushrooms are grown commercially, and wild mushrooms are collected mostly for personal consumption. But in many parts of the world, a wide variety of wild mushrooms are collected for sale and consumption. Fungi used for food are not limited to fruiting bodies such as mushrooms, however. Various species of lichens are eaten in Arctic regions as well as in parts of North America and Asia. In southwestern China, for example, several species of lichens are used as a primary ingredient in cooking.

There has now been a great deal of research that has been carried out on some of the fermented food products, so that the identify of the fungus involved in the process has been established. Some of the more familiar ones include miso, shoyu, tofu and tempeh. However, the microorganisms (this includes bacteria) involved in the majority of fermented food (there are approximately 500 of these) are unknown. Unlike Western cultures, in which fermented food is usually carried out by yeasts, Eastern cultures have utilized a number of different mycelial fungi.

Shoyu (soy sauce) is probably the most familiar Asian food product in this country, but probably few people know how it is made. All of you probably are aware that it is made from soybeans. The soybeans are cooked mixed with wheat flour, pressed into cakes, and placed in a special room where it is inoculated with Aspergillus oryzae (the same species used in making saki). The mixture is then incubated for three days. If all goes well the cakes will become covered with yellow mycelial growth. The molded cake is referred to as Koji, which is a fermentation product of grains. The koji is now mixed with salt and water and is now referred to as the Moromi. The moromi is then inoculated with a bacterium, Peiococcus soyae, which will ferment the mixture for approximately 6 months. The aged liquid which is pressed out is the soy sauce. Because it is a fermentation product, soy sauce does not spoil when left out.