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A. Beneficial Activities of Saprobic Fungi 3. Production of Food and Beverages
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3. Production of Foods and Beverages:
Among the tombs, stone and wooden sculptures and
other artifacts of the ancient Egyptian civilizations are numerous
depictions of life there almost 6000 years ago. Among these depictions
are scenes of bakeries, breweries, vineyards, and wine presses. This is
perhaps some of the first solid evidence of the use of fungi in
large-scale food and beverage production. Archaeological data, however,
are still unraveling the mysteries of “how long has man been doing
this?” Current discovery of the ice
man in the foothills of the Alps with cereal grain and mushrooms in
his pouch suggest that bread making and mushroom use may go back 10,000
years. And, the discovery of wine residues in clay urns in Iran date back
to 7,000 BC. Yet the discovery of the organism responsible of
fermentation that goes on in bread and wine making was not until 1680
when Antoine van Leeuwenhoek first discovered yeast cells under his
microscope. It was more than 200 years later before Louis Pasteur
concluded that through anaerobic respiration (fermentation) sugar was
converted into carbon dioxide and alcohol by such tiny yeast. While
yeast are central to the baking and brewing
industries, many filamentous fungi are utilized in the production of
cheeses and a wide array of exotic foods. We will examine first the use
of fungi in brewing and baking; then in the production of cheeses and
other exotic fermented foods and beverages. There are several types of bakers yeast (Saccharomyces cerevisiae). Compressed yeasts: What we commonly refer to as “yeast cakes” or wet yeast. It contains about 70% moisture and has a shelf life of about 3-4 weeks. Such yeast is perishable and should be stored under refrigeration (4-5º C). Crumbled yeast forms are similar to yeast cakes but with less water and in a crumbled condition. This type is often sold in 50 lb bags. Active Dry Yeast: Dry yeast is prepared similar to compressed yeast but is dried under specially controlled conditions. The moisture content is 6-8%, which enables them to be stored for a few months. Dry yeast should be revived in water at 105-110º F. Instant Dry Yeast: Through a quick drying process under controlled conditions, more porous yeast can be produced that become active immediately on rehydration. This is probably the most popular yeast used in home baking. a. Yeasts Fermentation in Bread-making. Bread
is a baked product made of dough that has been raised by yeasts or other
gas forming organisms. Why or when man first ate seeds or grasses,
learned to grind them into flour, mix the flour with water or milk and
bake it into bread is not known. Remains in the sediment of a Swiss Lake
dweller show that humans were baking bread about 10,000 years ago.
Archeological data reveal that bread making has been a central part of
almost all subsequent cultures of mankind. The Egyptians appear to be
the first to discover that letting dough ferment would result in light,
flavorsome bread. Until the last two centuries, however, light bread
was more or less restricted to nobility. Today, we all enjoy the noble
use of light bread. At the peak of the Greek Empire, several types of
bread were produced and baking later became a vital business in most
medieval towns (Sanderson
et al.
1983. Yeast fermentation in bread making. AIB Tech. Bull. 5:1-7). How to make a lot of dough? In the early years, bread making relied on natural fermentation. During the late 1700’s, commercially available yeasts were used in large-scale production of bread. Charles Fleischman of the U.S. introduced in 1886 a new type of compressed yeast for distillers and bakers. An average baking formula for white bread requires 100 lbs of white flour, 2 ½ lb of yeast, 2 lbs of salt, 6-7 lbs of sugar, 4 lbs of dry milk, and enzymes when sometimes needed. Modern mixers can handle more than 1600 lbs of dough. Larger US bakers have continuous mixers. By the mid 1960’s, more than 40% of bread making was done in continuous mixers. Close to 50,000,000 loaves of white bread are sold in the U.S. annually; it is a $5 billion dollar industry! Yeast is the essential ingredient in many bakery products, giving it lightness and a delicious flavor. The common baker’s yeast is Saccharomyces cerevisiae, a cellular, budding yeast. The use of fermentation in producing bakery products dates back to beyond 2000 BC where Egyptian hieroglyphics clearly depicts the practice. It was only in the 19th century that a scientific basis for the process was understood when scientists such as Charles Hansen of the Carlsburg Labs in Denmark developed methods of isolating and culturing pure strains of the yeast. The commercial production was a tremendous boost to the baking and brewing industries. Today, large tanks or fermentors are used to culture yeast. Water and molasses are commonly used and a supply of oxygen is admitted. It is estimated that approximately 1.4 million tons of compressed yeast is produced each year. b. Fermented Beverages: Ethanol
Production by Yeasts: For large-scale production of ethanol by
yeast, an organism that is tolerant to high concentrations of ethanol
and highly osmotic substrates is essential. Species of Saccharomyces
are the most tolerant to ethanol. Wine yeasts can tolerate levels up
to 20%, whereas, bakers yeast used in beer making and bakeries can
tolerate levels at from 4 to 6%. Most organisms are inactivated in
concentrations of ethanol above 15%. Extensive research has been done to
produce strains that will be effective in utilizing various
substrates and tolerate high levels of glucose or sucrose. They must
also be resistant to certain metabolites that may be toxic. Ethanol
tolerance is genetically controlled by a large number of genes (Ismail
& Ali, 1971. Fol. Microbiol. 16:300-359). Distilled
Alcohol:
Distillation involves
the conversion of a substance into a vapor that is subsequently
condensed to the liquid state. The process goes back to the time of
Aristotle (around 350-380 BC). Distillation is used in particular to
separate mixtures of liquids in which the boiling points of the liquids
differ. In the production of distilled alcoholic beverages, the
fermented substrates contain, water, alcohol, oils and other liquids.
The boiling point of alcohol is 79.3° C and that of water is 100°
C; thus the alcohol will vaporize at a much lower temperature. Its
vapor can be condensed in a cooling coil from the still and thus
separated from the other liquids. Species of Saccharomyces and Schizosaccharomyces
are used to produce distilled alcoholic beverages. Industrial
alcohol
is produced in the U.S. with corn as the primary substrate. In Brazil,
sugarcane is used in large-scale alcohol production for automobiles.
With the ever-increasing depletion of fossil fuel reserves, production
of ethanol from plant products is more attractive. With industrial
ethanol, flavor and other qualities are not as important as consumable
products. Therefore, the yeast strains used are selected for their efficiency
to digest substrates and in their tolerance to high levels of
ethanol. Alcoholic beverages
are made from a large variety of starchy or sugary products. Whiskey
is made largely from barley, but sometimes from other grains. They are
essentially aged grain alcohol that start out as clear but becomes
colored when aged inside of charred barrels. Bourbon
is a form of whiskey made from fermented corn, or occasionally other
grains. Vodka is
produced largely from potatoes in Russia and other east European
countries because they are cheap. They often use grains as well. Rum is
a distilled spirit made from sugar-containing substrates like molasses
and cane juice. It is initially clear, but like bourbon, it is darkened
by storage in wooden barrels; or in recent years adding caramel after
distillation. It is popular in tropical and subtropical countries where
sugarcane is grown. Cognac
is made from distilled grape wine and gets its name from Conacais,
France where it was first made. British and Dutch merchants began to
distill wine to prevent spoilage in shipment. Brandy
is made in a similar way as cognac, initially from grape wine but later
in North America from fermented juices of pears and peaches. Tequila is a briny liquor
made exclusively in Mexico from fermented juice of the Agave cactus.
The Mexicans were making a fermented drink 1000 years before they were
invaded by Spain. The Spaniards brought to Mexico with them the art of
distillation; hence, tequila came into existence. WINE Wine in the strict sense is the fermented juice of grapes. However,
wines are now made of many juices. The making of wine is known from the
earliest history of man; one of the earliest written is the Biblical
account of Noah (perhaps 5000 BC). To quote a recent report (Gainesville
Sun, June 5, 1996), “Talk about a vintage! Scientists say they have
found the oldest evidence of wine residue at the bottom of a squat, 7,000-year
old pottery jar. Traces of two chemicals in the jar, found in the
Zagros Mountains of Iran, extend the known history of wine-making
2,000 years.” The jar came from a time when people were first
establishing permanent settlements and were likely already cultivating
the grapes from which the wine was made. For centuries wine was stored
in flasks of animal skin or in clay vessels. During the rise of the
Roman Empire, wooden vessels as well as clay urns were common. The use
of bottles and corks became common towards the end of the 17th century. While wine making has gone on for centuries, the process was brought to this country by the early settlers. Perhaps the earliest wine making in the U.S. was done in Florida by early Spanish explorers. Yet today, only a few wineries occur in Florida (Fig. 5-1) where they use native muscadine grapes (Figs. 5-2; 5-3; 5-4).
Fig. 5-1. Lakeridge Winery near Clearmont, FL.
Fig. 5-2. The common muscadine grape.
Fig. 5-3. Scuppernong grapes.
Fig. 5-4. A common variety of grapes used in wine-making. Much of our Florida wine making was with the assistance of Prof. Robert Bates at the University of Florida. (Images of wine making used in this website were provided by Dr. Bates) Larger wineries use mechanical pickers (Fig. 5-5), while smaller growers still rely on hand picking (Fig. 5-6).
Fig. 5-5. Mechanical harvesting of grapes.
Fig. 5-6. Handpicking of grapes. Grapes are hauled to the winery (Fig. 5-7) where they are tested for sugar content and then placed in large juicers (Fig. 5-8).
Fig. 5-7. A load of grapes going to the winery.
Fig. 5-8. A large grape press. The juice is piped to fermentation tanks (Fig. 5-9) where yeast is added . Some wines are distilled to make cognac, others are allowed to ferment in large insulated tanks (Fig. 5-10).
Fig. 5-9. Computer controlled piping of juice to fermentation tanks.
Fig. 5-10. Large sedimentation/ fermentation tanks. After proper fermentation, the wine is stored in wooden barrels for aging (Fig. 5-11).
Fig. 5-11. Wooden barrels used in aging and storing wine. Barrels are transferred to cool, dark rooms for lengthy storage. The wines are then tested for quality and taste. After proper aging, wine is bottled (Fig. 5-12) and further quality control is done. Two common Florida wines are Noble and Stover (Fig. 5-13)
Fig. 5-12. Wines being displayed for judging.
Fig. 5-13. Two of the common Florida wines. Wines
are named after the type of grapes or the geographic area or specific
village where they were first produced. For example, Burgandy,
Bordeaux, Champagne, and Alsacs
are important wines of France. During the 17th century, wine makers in
the Rhine valley found that grapes allowed to rot on the vine gave the
wine a sweeter taste. There are three basic types of wines, (1)
table wines, (2) fortified wines, and (3) sparkling wines. Table wines are made from pressed grapes fermented in vats with the
addition of sugar, yeasts, sulfur dioxide. Saccharomyces
ellipsoideus is the common yeast used in the fermentation process. The alcohol content
is around
12-15%. Sulfur dioxide is used to keep down the vinegar producing
bacterium Acetobacter. Wine
may be chilled in vats to cause sedimentation and the “free run”
wine is decanted. Fortified wines
receive an addition of alcohol, brandy or other alcoholic beverages, and
the final alcohol level is from 16-23%. A common fortified wine is
port
wine which gets it name because sailors who used to come into port
would purchase wine spiked with brandy or liquors to give a greater alcohol
level. Sparkling wines such
as champagne go through a double fermentation in which the alcoholic
content reaches 20%. Some sparkling wines have a natural effervescence,
others are made effervescent by bubbling them with carbon dioxide. All
natural wines are below 20% alcohol because beyond that level, the
fermenting yeast would be killed. There are red, white, and pink (rosé) wines, Red
wines are made from
black grapes in which the
husks (mush or skins) are left in contact with the juice throughout
fermentation. Most white wines are made from green colored grapes or from black grapes
in which the husks are removed soon after pressing. Leaving the husks of
black grapes in the fermenter for a short period of time produces a pink
wine. European wine production was almost devastated when
in the 19th century imported American rootstock infested with a louse,
Phylloxera, which feeds on grape
roots, destroyed more than 2,500,000 acres throughout France and
surrounding countries (Fig.
5-14;
Fig.
5-15). Many growers never recovered.
Others imported resistant rootstock and the industry was soon
reestablished. CLICK HERE TO GO TO TOP OF RIGHT SIDE COLUMN
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Fig. 5-14. Leaf galls caused by the louse Phylloxera. Fig. 5-15. Severe root damage caused by Phylloxera. BEER
Beer is a beverage obtained by the alcoholic fermentation by yeasts of a
malted cereal, usually barley malt, with or without other starchy
materials, and to which hops have been added . (For more
information on beer-making, see Hardwick, 1983. Biotech.5:166-229).
Brewing seems to have originated in the Babylonian Empire (Mesopotamia)
before 6000 BC. By 2000 BC, many types of beer existed in Babylon. There
is evidence that the brewing of beer developed independently in Egypt.
Some have suggested that the Hebrews learned to use hops to flavor beer
while they were in captivity in Babylon during the 8th and 9th century BC.
The Greeks learned to make beer from the Egyptians and the Romans in turn
learned from the Greeks. There are two types of beers, lager and ales. Lager beer employs bottom fermentation in which the “spent yeast” settles to the bottom and the green beer is aged. With aging, it mellows and is carbonated with C02. In the brewing of ales, the yeast selected is a top fermenter, forming a foam that can be removed. Enzymes are often used in the early stages of brewing, i.e. the “mashing” stage, and later in the brewing process. Amylase produced by other fungi increases starch digestion and results in low carbohydrate, or “lite” beers. Several other carefully monitored enzymes are added during the brewing process. Without protease, for example, beers would become hazy, and glucoamylases produced by certain species of Aspergillus are used to sweeten beers. Four things are vital to brewing beer, barley malt, hops, water, and yeast. In the making of barley malt, barley is allowed to go into dormancy after harvest. During malting certain enzymes are formed within the grain. Before malting the barley is soaked in water to initiate germination, after which grains are dried to about 2% moisture level. Timing of germination, temperature and duration of drying, and other factors affect the kind of malt that is produced. Corn, rice, and other grains may be added as adjuncts to add texture and flavor. These are closely guarded industry secrets. Hops are not essential for the manufacture of beer. The flowers of the female hops plant are used, and only from unfertilized flowers. Pollinated hops will give the beer a bitter flavor. Hop growing in the U.S. is chiefly in Oregon, California, Idaho, and New York. The best hops for brewing come from Slovakia and the Czech Repuplic (formerly Czechoslovakia). Hops are added to mashed malt solution (wort) during boiling. Water quality is vital to beer production, especially pH. Alkaline or “hard” water gives poor results and water with sulphur, iron, or bacteria should be avoided. Apparently, there must be ideal water in the mountains around Golden, Colorado! The yeast used in beer brewing is Saccharomyces cerevisiae (Fig. 5-16).
Fig. 5-16. Yeast being added to the mash during beer making. The main stages of brewing are mashing, boiling, and fermenting. Prior to
mashing, malt is crushed between rollers to form flour. Mashing involves
adding water (100-150F), solubilizing the starch by enzyme action, and
separating out the husk. After mashing, the “wort” is boiled in large
copper tanks or kettles, stopping enzyme action. The wort is filtered and
passed into a high-speed centrifuge to achieve clarity. It then passes
into large coolers. Fermentation begins when yeast is added to the cooled
wort at 1 lb/barrel. After about 8 days most all fermentable substrate has
been converted into alcohol. The beer is then bottled, canned, or stored
in large kegs for marketing. The following images show the various types
of cookers, fermentation tanks, and sediment tanks utilized in the
manufacture of beer (Fig.
5-17;
Fig.
5-18; Fig.
5-19). The manufacture,
distribution, and sale of beer are major industries in the U.S. and in Florida.
Fig. 5-17. Large kettles used in cooking the wort.
Fig. 5-18. A mash cooker.
Fig. 5-19. A brew kettle. OTHER TYPES OF FERMENTED PRODUCTS
Kanji:
A beerlike beverage made with carrots and beets fermented with Hansenula.
Taste much like cherry wine. Toddy:
Sweet fermented sap from tropical palms using Saccharomyces
cervisiae (Fig. 5-20).
Many substitute organisms can be used.
Fig. 5-20. A large pouch with fermented palm juice (toddy). Others fermented products include: Shoyu (=soy sauce): This is one fermented product well recognized throughout the US and Europe. Shoyu, referred to as Ketjap in Indonesia, has been produced in Japan for over 1000 years. The average Japanese consumes more than 3 gallons of soy sauce per year. Shoyu is prepared by soaking soybeans for 15 hr and autoclaving them for 1 hr. Clean, roasted wheat powder is added. After cooling, a starter, tane koji composed of Aspergillus oryzae or A. soyae is used as the inoculum. After fermentation for 3-4 months, or up a year, the material is combined with equal parts of brine and placed in tanks. The resulting mash is compressed and the liquid supernatant is retrieved, sterilized and bottled. Tea
Fungus:
Perhaps one of the strangest fermentations encountered is the so called
“tea fungus” of eastern Europe and Asia sometimes referred to as Hongo.
This drink is made from dry tea leaves steeped in a liter of water, and
the leaves removed and 100 gm of sugar added. The solution is autoclaved
and a “starter” culture is added and the material is allowed to
ferment. Two yeasts and Acetobacter have been isolated from the starter. Anchu
is an alcoholic drink in Taiwan made from red rice. Awamori
is an alcoholic drink prepared from sweet potatoes in Japan. Braga
is a fermented drink made from millet in Romania. c. Cheese Making: We do not know when and where cheese was first made; its discovery was probably an accident (Fig. 5-21).
Fig. 5-21. A depiction of early cheese making. In the Judeo-Christian Bible, II Samuels 17:27-29 says that cheese of the herd was given to King David (approx. 1000 BC). So, cheese has been around for a while! The production of cheese is a multimillion dollar industry in the US and is also a dominant industry in other countries. It involves the fermentation of milk from different animals, using various organisms, and processing them under rigidly controlled conditions. Milk is coagulated, the liquid whey removed, and the solid curd is preserved. Curd may be made in three ways: acid coagulation, heat coagulation, and rennet coagulation. There are block cheeses, powdered cheeses, soft cheeses, and various processed cheeses. Ricotta and similar cheeses are made from heat coagulated curd (Fig. 5-22).
Fig. 5-22. The solid portion of coagulated milk referred to as curd. Cottage cheese and cream cheese are made by the acid coagulation of curd by lactobacillus or other bacteria that ferment milk. Rennet curd is made by an enzyme from young calves that coagulates milk. Most of our common cheeses use rennet curd in their production. Several steps are used in the process of making curd (Fig. 5-23; Fig. 5-24).
Fig. 5-23. Separation of the solid curd and the watery whey.
Fig. 5-24. Curd ready to cut. Cheeses are packaged and sold in a number of forms (Fig. 5-25).
Fig. 5-25. Various types of processed cheese.
Two of the most common cheeses in which filamentous fungi are used in
fermentation are Camembert and Roquefort. Camembert Cheese originated in the town of Camembert in the Normandy district of France. Legend attributes its discovery to a milkmaid, Maria Harel, who first shared it locally with neighbors. This blue cheese is now marketed worldwide and is manufactured in a number of countries. Camembert cheese, also called Brie, obtains its flavor and texture from lipolytic and proteolytic activity of molds belonging to Penicillium camemberti and P. casicolum (Fig. 5-26).
Fig. 5-26. Penicillium camemberti as seen in culture. Thom & Raper, (1968. A manual of Penicillium, Hafner Pub. Co., NY). Pitt (1985, Common species of Penicillium, CSIRO Div. Food Sci., N. Ryde, NSW, Australia) concluded that P. casicolum is only a mutant strain of P. camemberti. Other species of Penicillium have been used to produce soft cheese, but P. camemberti is preferred by judges. The fungus grows only on the surface of the cheese, secreting its metabolites with flavor into the cheese (Fig. 5-27).
Fig. 5-27. Two of the most common fungal derived cheeses, roquefort (A) and camembert (B). The production of camembert cheese requires rigidly controlled conditions or else other fungi, particularly Scopulariopsis brevicaulis, will ruin the cheese. For this reason, it has been very difficult to establish a successful industry in other countries. Camembert cheese has not gained wide popularity in the US. Roquefort Cheese is made from the fermentation of milk curd by Penicillium roqueforti (Fig. 5-28), a species first isolated in 1904 and described by Thom (1906, USDA, Bur. Animal Ind. Bull. 82).
Fig. 5-28. Cultures of Penicillium roqueforti. There are apparently many strains of this fungus, some of them being described as distinct species. Thom and Raper (ibid.) discuss a dozen such strains. The different enzymes produced by P. roqueforti results in various cheese flavors. P. roqueforti is a common fungus on the surface layer of silage. This is a likely source of the original clones that were discovered in the production of cheese. Charles Thom, USDA, Peoria, IL, introduced the production of roquefort cheese in the US in 1906. Thom and co-workers discovered the lipolytic and proteolytic enzymes of the mold released caproic, caprylic, and capric acids which imparted flavor to roquefort cheese. Unlike Camembert which has only surface growth of the fungus, the veins one sees in blue cheeses are zones of Penicillium growth within. Other blue-veined cheeses similar to roquefort are Dolce Verdi produced by Penicillium expansum and Ellischour, with a red pigment, produced by P. nalgiovensis. Other blue cheeses include fromage blue cheese in central France (from sheep and cow milk); gorgonzola in northern Italy, stilton in England, cammelost in Norway, and neufchatal in Germany. |
