Role of Yeast in Production of Alcoholic Beverages

Microscopic image of Mackeson Triple Stout at work, courtesy

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Although there is a distinction between beer, wine and liquor as well as other lesser known alcoholic beverages, they share one thing in common. They are the fermentation products of yeasts, mostly Saccharomyces cerevisiae or in the case of beers, usually S. carlsburgiensis. Yeasts, as you recall, are not mycelial. They are unicellular fungi that reproduce asexually by budding or fission. The reaction by which alcoholic beverages are produced is generally referred to as fermentation and may be summarized as:

Yeast + Glucose è Alcohol (Ethanol) + CO2

This reaction is also important in baking bread, but the desired product is then the carbon dioxide rather than alcohol. The production of alcohol occurs best in the absence of oxygen. However, from the yeast’s point of view, alcohol and carbon dioxide are waste products, and as the yeast continues to grow and metabolize in the sugar solution, the accumulation of alcohol will become toxic when it reaches a concentration between 14-18%, thereby killing the yeast cells. This is the reason why the percentage of alcohol in wine and beer can only be approximately 16%. In order to produce beverages (liquor) with higher concentrations of alcohol, the fermented products must be distilled.

What’s the Difference Between Beer and Wine?

Generally, beverages derived from fermented fruit juice is wine. However, commercially speaking, “wine” is fermented grape juice from Vitis vinifera. Other wines are specifically referred to by the name of the fruit of the juices from which they are fermented. For example, elderberry wine, peach wine, etc. Beer on the other hand is usually derived from fermentation of malt derived from the digestion of germinated barley grains, in western cultures, but other grains may be utilized in other cultures. There is also a difference between processes by which wines and beers are fermented.

There is a perception, perhaps just my own, as to the people that drink beer and the ones that drink wine. Beer drinkers seem to be “blue-collar.” When you get together with friends after you played a softball game or touch football game, there is usually lots of beer. When you go to professional baseball and football games, beer is the beverage most often purchased, not wine. Wine, on the other hand, is a beverage consumed in expensive restaurants, at formal dinners, social affairs, etc. People that drink only wine seem to be the “white-collar people. However, if we compare beer and wine making processes, you might have just the opposite impression. Beer making is almost a science. Compared to wine making, it is rather complex and there’s a purpose for everything that is done in making beer and the beer makers know just about everything that goes into beer. Wine making, on the other hand, is relatively simple. It’s truly a natural drink and its origin probably preceded beer making. Anyone can do it. The yeast responsible for fermenting the sugars in the fruits are usually present in the grape skins, and fermentation will occur whenever there is a break in the skin (take a deep breath the next time you go hiking and pass a bunch of guava fruits that have fallen to the ground). So when human production of wine began, it involved collecting fruits, crushing them and allowing them to ferment, a much simpler process than making beer.

History of Beer Making

The making of beer has become a popular hobby and many people now brew beer in their homes. The necessary ingredients and a recipe for beer making, as well as a variety of beer recipes, can be found in the following page. Note, the link for the beer recipe is “framed” so you must click on the links within to go to the general beer making recipe and the beer recipes, respectively. In addition, knowing the modern process of beer making will help you appreciate how beer making has evolved in the many thousands of years since its origin.

Some historians believed that beer may have existed before the dawn of civilization while the human species was still made up of numerous nomadic tribes. However, most believed that it came about early in various civilizations. The manufacturing of beer is more complex than wine and it has been mastered by many cultures in different ways. The ancient Mesopotamians and Sumerians were brewing as early as 10,000 BC. However, clay tablets, with a recipe for beer, from approximately the year 6,000 B.C., in Babylonia, is the first documented evidence of beer making. This recipe utilized underbaked bread made from germinated barley. Being underbaked, the bread serves as a live yeast culture and when the bread was cut into small pieces and placed in a large jug with water, malt would be produced. The preinoculated malt when left out will ferment to give you beer. Although crude, the “common” people considered this beverage ready to drink. However, someone with “breeding” would usually filter this mixture before drinking. Dates, herbs and honey were sometimes added for flavoring. Note that early beer did not include hops in their recipe, which would not be included until centuries later. Although the recipes for their beer was also far different than today’s bottled varieties, it is still recognizable as beer. In ancient China rice was used to make a rice beer and in pre-Columbian civilizations in the Americas, corn was used instead of barley and, without knowing it, added their own enzyme to break down the starch by first chewing the corn before placing it in the fermentation tank. The saliva from their mouths served as the enzyme in the process of starch conversion to sugar and gave their beer its improved and distinct flavor. In rural areas of Russia, kvass was made by adding pieces of stale, black bread to malt, flour, sugar and water, and allowing this mixture to ferment. This resulted in a concoction that was only 1-2% alcohol, but the Russians have maintained production of kvass for several hundred years.

It is interesting to note that historically, beer production, in many cultures, was considered to be woman’s work, along with the production of other edible product such as butter and cheese. In fact, the origin of beer in many cultures is attributed to women. The Babylonians to Siris and in Rome beer was dedicated to Ceres who was the Goddess of the Corn and their name for beer was cerevisia, which is the derivation for the specific epithet for brewer’s yeast S. cerevisiae. Since women were considered closer to the corn goddess, they were made the priestesses of these goddesses as well as the brewers in various cultures. In all cases beer was considered a heavenly gift. The Norse believed their beer was the drink of Vahalla, their heaven for those who died in battle and in China beer was simply a gift from heaven.

In Western culture, during the Middle Ages, brewing was a household art in which every girl was instructed, along with baking, since both involved the same ingredients and mysteries. Beer was considered “liquid bread” and a meal would consist of beer, bread and cheese. The role of women and beer would continue until the Middle Ages, when monasteries began to make beer, and brewing then became a male dominated process. It was also at this time that hops was introduced into the process of beer making, which served as a flavoring, but more importantly, a preservative, which gave beer a longer shelf life.  Although early beer was not necessarily very tasteful, one reason why beer was adopted as the beverage of choice, in many early cultures, was because water was often of poor quality and contaminated. The Roman armies carried beer with them as they journeyed to conquer distant lands in order to avoid becoming ill in foreign lands. When an area was conquered, Roman yeast was introduced by using the wort from previous batches of beer to ensure that they would have a decent drink. Skipping ahead in time, Bohemia, historical region and former kingdom of present-day western Czech Republic, had established state breweries, in 1256, in the town of Budweis, and by 1384, Pilsen’s breweries were under the control of Charles IV (Holy Emperor of Rome, 1316-78). Beer also had impact on languages. In Germany, if the local beer went bad, beer would be imported from another town and sold at cost in the basement of city hall – the ratskeller: Literally council basement. Today, a ratskeller is a restaurant or tavern, usually below street level, that features the serving of beer. A custom of medieval marriages, in England,  had the bride’s family brew a special “bride’s ale”, for the bride. The bride’s ale eventually became the present bridal. Even the word “ale” is derived from the medieval hael, meaning “good health.”

Government also used beer as a means of collecting taxes. Since beer was made at home, it was impossible to impose a tax directly. However, taxes were levied on the ingredients that were required to produce beer as well as on alehouses. Churches were exempt from this tax since on the grounds that they consumed their own products, but churches often required the community to buy their beers. Because of the resentment of this practice in England, this was but one of the factors that led to the overthrow of the Roman Catholic Church. However, it would not be until after the Reformation and the weakening of the church that brewing became the responsibility of commercial brewers who could be taxed for the beer they brewed.

By the time that the New World was invaded by Europeans, beer was already present. Columbus drank corn beer offered to him by Native American Indians. It is said that the dwindling supply of beer, aboard the Mayflower, in 1620, was what led to the selection of Plymouth as the end of the voyage for the Pilgrim. Beer was considered such a necessity by some of the early settlers, such as George Washington and William Penn, that they started their own breweries. The English initially imported beer from England, but by 1629 began their own local breweries. The Dutch, on the other hand, started their own breweries, immediately. These early beers were all ales and it would be until 1840, when German immigrants started breweries that lager beer would be introduced. Among some of the people that started these German breweries were Frederick Pabst, Bernard Stroh, Joseph Schlitz, Adolph Coors, Henry Weinhard and Theodore Hamms. Their lager beers soon displaced the ales, in popularity.  By the mid 1600’s, breweries were well established in the New World.  Beer even contributed to higher education for women, in 1861, when Matthew Vassar invested his fortune, earned in beer, in establishing Vassar College.

With the exception of Prohibition, during the 20th. Century beer has been largely mass-produced and automated. There were approximately 4,137 breweries in the United States in 1876 producing quality beer. This number fell to 1,100, in 1919, the year before Prohibition. After Prohibition was repealed, only 700 breweries reopened. By the 1970’s fewer than 40 breweries remained. Most of these beers were very uniform and bland. The United States had by this time developed a reputation for having the world’s worst beer. There were reasons behind this. After WWII, in order to appeal to women, milder tasting beers were developed. Thus, the origin of “light” beer. However, such beers only sold modestly well. It would not be until 1972 that cigarette maker, Philip Morris, would change the face of American beer as well as advertising. Philip Morris acquired Meister Brau and its Lite label that year and renamed it Miller Lite. Using a sophisticated and massive advertising campaign, using well known former athletes, Miller moved from seventh to second place among U.S. brewers. They were the ones that came out with the slogan: “all you ever wanted in a beer, and less.” Thus, business came to realize that promotion of the product and not necessarily product quality that determines the success of a product.

The Science of Beer Making

Today, beer is consumed in vast amounts in this country, and beer making is largely automated as in all mass produced products. Despite the sophisticated machinery that is used in brewing beer, it’s still essentially the same procedures that has been used for hundreds of years. We will see a video on the making of beer on Thursday that will demonstrate the process that we have just covered.  However, beer making has become very sophisticated because of the advances in knowledge that has resulted from advances in science. Prior to, and even during the 1800’s, there were many who knew how beer could be made, but none knew of the science behind each step. It was not until the 19th. century that it was realized that during germination, of cereal grains, that enzymes were released that would not break down not only the barley starch and protein into simple sugars and amino acids, but would also do the same for other carbohydrates, such as potato, corn and wheat. This realization cheapened the cost of making beer since germinated barley is a greater investment than the utilization of potato, corn and wheat. It would not be until the 19th. Century that it would be known that yeasts were the organisms that actually were responsible for the fermentation process.

Although the process of fermentation had been used for thousands of years, it was thought to be a magical rather than a material process. As a result, many rituals and superstitions developed to direct and control fermentation. By the 17th. Century, it was known that yeast was present during fermentation, but its role was controversial. There were two opposing views on this subject. One view was that yeast was required for the fermentation process, while the other argued that the process was purely chemical. It was not until Louis Pasteur’s work, in the 1850’s and 1860’s, was this argument resolved. Pasteur was asked by the distillers of Lille, where the manufacture of of alcohol, from beet sugar, was an important local industry, to determine the problem of lactic acid production in their alcohol. Upon examination of the fermentation product under the microscope, Pasteur was able to observe the usual yeast cells, but also noted that there were a large number of smaller rod- and sphere-shaped cells. When Pasteur placed a small amount of this material in a sugar solution, a vigorous lactic acid fermentation occurred along with the formation of a grayish deposit in the solution which proved to be the rod- and sphere-shaped cells. Successive transfers of these cells always resulted in production of lactic acid fermentation and an increase in the number of cells. Pasteur argued that the cells were a new “yeast” that specifically converted sugar to lactic acid during its growth. It would be years later before it was understood that the new “yeast” were actually bacteria. Using a similar method, Pasteur studied a number of organisms and their fermentative processes. He was able to show that the different fermentation products produced were invariably accompanied by specific microorganisms. This discovery, however, had further significance. Just as the different microorganisms caused different fermentation products from sugar, so did different diseases arise as a result of different microorganisms, and that these microorganisms did not arise spontaneously, as once believed, but that each microorganism was derived from pre-existing cells of the same type. This also led to the concept that by destroying the microorganisms in food products and beverages or by preventing their appearance in sterile products, spoilage could be prevented. This concept led to the heat treatment of food products and beverages that we now know as pasteurization.

In the beginning of beer making, beer was an alcoholic beverage with the flavor of malt and grain. It was flat, slightly sweet and would spoil quickly. It would not be until the 8th. Century, that brewers in central Europe found that the addition of Hops flowers preserved the beer and gave it the slightly bitter taste that made it more palatable. However, Hops was not the only bitter additive used. Various cultures used other bitters; tannins from Oak and Ash trees were used in Scandinavia; cinnamon in southern Europe and in America sweet fennel, licorice or sassafras was used. Nevertheless, by the end of the 15th. Century, it was Hops that became the standard bitter and preservative added to beer. Only in England was there resistance to the use of Hops, but they, too, accepted it by the end of the 16th. Century.

With the genetic manipulation of yeasts, numerous varietal strains have been bred. This, along with modifications in the brewing process have led to different types of beers. Those most often seen in North America include:

  • Lager. Beers made with yeast that settle on the bottom (Saccharomyces carlsbergensis) of the container used. Thus, all the yeast and other material settles on the bottom which results in a clear beer. Most American beers are lagers.
    • Pilsner. A colorless lager beer originally brewed in the city of Pilsen. Water used for this style of beer tend to be harder, with a higher calcium and magnesium content than water used for lager. The color of pilsner is also lighter than that of lager beer.
  • Ale. Beers made with yeast that floats (Saccharomyces cerevisiae) to the top of the brewing vats, resulting in a cloudier beer. They tend to have a higher alcohol content than lagers.
    • Stout. A very dark, almost black ale. The dark color and roasted flavor is derived from the roasted barley, and/or roasted malt. Beer historians consider it to be the descendant of Porter ale.
    • Porter. A very dark ale. The darker color and special flavor comes from toasting the malt before brewing. This usually results in a stronger taste and higher alcohol content. Considered by beer historians to have evolved into the Stout ale.

History of Wine

As in the case of beer, the place and time of origin of wine is uncertain. Because of the number of different types of wine that are produced, we will restrict our discussion to grape wine. The species of grapes used in most wines is Vitis vinifera and is known to have been “domesticated” before 4,000 B.C. Wine made before this time probably would have used wild grapes. Unlike beer, women were not associated with wine. In ancient Greece, Dionysus gave wine to man and his Roman counterpart, Bacchus, was the God of Wine. In Hebrew folklore, it was Adam who planted the first grapevine.

Around 600 B.C., wine grape cultivation spread from the Mediterranean region to France and later to Spain, Portugal and Algeria. Until recently Europe and North Africa were the world’s leader in quality and quantity of wines produced. Now the United States, Argentina and Russia rank among the top 10 wine producing countries of the world.

In the United States, the quality of wine produced were poor to begin with because the New England area, which was the part of North America that was settled first, was not favorable for growing European grapes. However, there were other areas where growth would be better. Although not part of the United States at this time, California began cultivating grapes around 1769 and by the middle of the 19th. Century, California had a small but respectable wine industry.

Making Wine

Wine is made today much the same way that it was centuries ago. However, unlike beer, there is still a great deal that cannot be controlled in the production of wine. You will see this as we discuss the process.

The grapes from which the wine is to be made is first separated from the stem (stemmed) and then crushed in order to release the juice. The combination of the skin, juice and seeds is called the must. Grapes may be crushed by various means, from stomping on them with bare feet to the use of sophisticated electric presses.

If the desired product is a white wine, the free juice is transferred to a fermentation tank and the peels and stems are removed and pressed again. The juice of the second press can be added to the original juice or used to make another lower grade wine. If red wine is the desired product, the skins of the grape go into the fermentation tank with the juice. The red color of this wine is from the red pigment in the epidermis of the grape skin. Various vessels may be used as the fermentation tank. The most inexpensive and commonly used vessel is a 32 gallon, plastic garbage can.

Once the juice is in the fermentation tank, preferred strains of yeast are often added, but are not needed. The skin of the grapes already have adequate yeasts on them that this step could be omitted. This is one of the uncontrolled quality of wines. Since the yeasts that grow on the grapes vary in different vineyard, especially if they are in different countries, the quality of the finished wine will also vary (this is probably the basis for the claim that one country’s wine is superior to another). The addition of the preferred yeast gives some measure of control to the end product. Sulfur dioxide is normally introduced into the juice at this time to kill bacterial growth that may spoil the taste of the final product. Fermentation is allowed to continue for about eight to ten days, after which the initial wine is drawn off of the skin, if it is still present. Any liquid obtained from the skins that remained during the fermentation is considered to be of a poor quality and is used in poorer quality wines or for vinegar.

After the initial fermentation, the liquid is allowed to ferment for 20 days to about a month. During this second fermentation, the dead yeast cells as well as other particulate matter settle to the bottom. When this process is complete, the wine is separated from the sediment and transferred to an aging tank. As the aging process continues, more sedimentation occurs, and the wine is often transferred across a series of tanks during aging. This process is known as racking. If the final tank is a wooden cask, this also adds another uncontrolled quantity into the final product. Because wooden cask cannot be cleaned, they provide a unique character to the wine some of which are said to make the wine “superior.” However, the use of stainless steel vats have removed this uncertainty.

The aging of wine is variable. For white wines, usually one year to eighteen months, but red wines can age for as long as five years. At stages during aging, the wine is sampled and judged by a wine master. The fate of the wine is dependent upon the decision of the wine master. The wine may be bottled after aging is complete or used only as a blend to make an inferior wine. The bottled wine, again, based on the decision of the wine master, may be aged longer in the bottles or sold immediately after bottling. Thus, is the variability of the finished wine product.

White wines can benefit from aging for up to five years, after which they will tend to deteriorate. Red wines, on the other hand, can continue to improve for thirty or even up to forty years.

The above wines are “still” wines because they are fermented in open tanks and contain no gaseous carbon dioxide. If fermentation stops before the sugars have all been metabolized by the yeast, the finish product is a sweet wine. If all the sugars have been metabolized, the wine is said to be dry. As in the case of beer, the percent alcohol content will be 14-18%. However, in fruit wines, the percentage is lower because the amount of sugars in other fruits are generally lower. Even with the addition of sugar, fruit wines are generally 5 to 7% alcohol.

A detailed recipe for red and white wines can be downloaded from the Viticulture and Enology Department at the University of California at Davis. They have a nice web page on making wine at home, with wine making recipes in pdf files.

Champagne and Other Sparkling Wines

In order to obtain carbonation, extra sugar is added to yeast while the yeast is still actively fermenting and then tightly cap. The build up of carbon dioxide will carbonate the beverage to give you the bubbly effect. This is somewhat tricky since if too much fermentation occurs, the tightly sealed bottle can explode from the built up pressure. What about really cheap champagne? The price of the champagne does not necessarily mean that quality is lacking. Some champagnes are cheap because they are mass produced in large vats rather than handled as individual bottles.


A beverage that is non-alcoholic that came to the attention about ten years ago is commonly known as Kombucha, but has many common names. It is also known as the “Tea Fungus”, “Manchurian Mushroom”, and “Fungus Japonicus”, just to name a few. However, these names, as is the case with many common names, are misleading. The “fungus” in this case is actually a composite organism, composed of bacteria and fungi, none of which are mushrooms. The organisms involved are:

  • Acetobacter xylinum
  • Acetobacter xylinoides
  • Saccharomycodes ludwigii
  • Schizosaccharomyces pombe
  • Saccaromyces cerevisiae

The first two are bacteria and the last three are yeasts. When put together, they have an interesting appearance. They have the color and consistency of a fillet of sole and looks somewhat like “fish cake”. However, do not try to eat it, apparently when consumed in this matter, it is somewhat toxic! The Kombucha fungus is pictured below:

The first record of its appearance was in 221 B.C., during the Tsing Dynasty, in China. Thus, like the alcoholic beverages, it is also an old beverage. It was used as a herbal remedy and currently is popular for that reason. The tea that is made from Kombucha is said to a remedy for many ailments, arthritis, high cholesterol, high blood pressure, cancer, AIDs, and many many more. However, there has been little scientific research done on the virtues of this beverage, but it is probably safe to say that many of the claims made of this beverage are “exaggerated”.

The recipe for making the tea from Kombucha (40 fluid ounces) that I was given is:

  • Boil 40 fluid ounces of water in metal container, with a lid.
  • After boiling, add one third to one half cup of sugar.
  • Add two regular size tea bag or an equivalent amount of tea to water.
  • Allow tea to steep for 10 to 15 minutes and then remove tea bag.
  • Cover tea and allow to cool to room temperature.
  • Pour tea into a 64 fluid ounce glass container.
  • Pour 8 to 12 fluid ounces of previously made tea or a piece of Kombucha fungus into container.
  • Cover tea with unbleached filter paper held in place with a rubber band.
  • Allow to incubate for about a week before drinking. You should see the beginning of a new Kombucha fungus growing at the top of the tea at this time.

Guenther’s Web site, in Germany, also gives a variation of the above recipe, but has pictures. If you have difficulty visualizing what is done in the above recipe, you may want to visit that site.

Mycological Terms

There are a large number of brewing and wine making terms. I have only included a few, below. If you are interested in looking up more terms, I have included links to glossary for brewing and winemaking.

Beer: Any alcoholic beverage produced by the fermentation of sugars obtained from grain. In western culture, barley is the grain generally used.

Ethanol: Alcohol that is the metabolic product of yeast in the wine and beer making. Specifically, it is produced by the yeast during fermentation.

Fermentation: The process by which yeast converts sugars into alcohol and CO2.

Hops: Flower of hops added as ingredient to beer that gives it a bitter taste. However, it also serves as a preservative that gives it a longer shelf life.

Kombucha: A tea that is brewed with several species of bacteria and yeast and said to be of medicinal value. Also known as Manchurian Mushroom Tea, Fungus Japonicus and Tea Fungus.

Wine: Usually fermentation of grape juice, but may also be other fruit juices as well, e.g., elderberry, peach, apple, etc.

Yeast: In wine and beer making, the “ingredient” that converts the simple sugars into ethanol. The most common species used are Saccharomyces cerevisiae and S. carlsburgiensis. However, other species are also used.

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