Zymology and Zymurgy

Summary

Zymology is the study and science of fermentation, particularly in the production of wine and beer and in baking. Zymurgy refers to the applied chemistry aspects of alcoholic fermentation in the making of beers, wines, and liquors. (The term "zymurgy" is often used interchangeably with "zymology.") In the process of fermentation, sugar molecules are converted to ethanol and carbon dioxide. Although the most well-known fermentation agent is perhaps Saccharomyces cerevisiae, a budding yeast popularly used by brewers and often referred to as brewer's yeast, numerous other strains of yeast and other microbes have been cultured to impart specific properties to the resulting brew, including enhanced alcohol content, altered carbonation, and specific flavorings. In addition, the fermentation process is used in biosynthetic methods to produce specific modifications in chemical substrates that are difficult to achieve by standard in vitro (controlled-environment) chemical methods. Fermentation processes using algae and other microbes have been developed to create biochemicals and specialty pharmaceuticals.

Definition and Basic Principles

Zymology is a traditional process that predates the sciences of biology and chemistry by several thousand years. The basic process of fermentation has not changed in principle over that entire span of time, however. At its heart, the fermentation process is nothing more than the normal growth of yeast cells or other microbes in a suitable environment. Yeast cells are found in abundance as airborne material. Such airborne yeast is the main reason that many foodstuffs go bad when left exposed to the air, even briefly. In a mixture that contains free sugars in a water-based medium, such as an open pitcher of fruit juice, yeast cells may settle from the air and begin to reproduce in the mixture. The liquid will eventually become carbonated and effervescent because of carbon dioxide produced during the fermentation process, and it will acquire a decidedly acidic or sour taste. The solution may also become cloudy because of the population of microbes.

Zymology and zymurgy have developed as the practical and purposeful application of the fermentation process for the traditional production of alcoholic beverages for human consumption. The scope of their application has been broadened considerably, and they have come to be considered part of the foundation of the biotechnology and bioengineering industries. In practice, zymologists examine ways to apply known fermentation processes to new purposes beyond the traditional baking and brewing applications. This includes the development of new genetic strains of yeasts and other microbes and the development of effective substrate systems to maximize the production of specific materials.

In any fermentation process, a specific microbe is provided with a controlled environment in which to grow in an uncontrolled manner. This may be a sealed or isolated container of some sort that has been fitted with appropriate equipment to ensure thorough mixing of the contents. Those contents consist of the microbial culture and the nutrient medium in which the culture will grow. The environment may also be an open but sequestered collection of some appropriate substrate material on which the microbial fermentation process will act. The microbial culture is typically grown in a batch process, but continuous production methods can also be employed, depending on the desired output. The output of the process is then captured and recovered by separation methods that return the microbial culture to service.

In some cases, the purpose of the process is to produce more of the microbe, as when yeast cultures are grown to supply needs for particular strains in specific applications. In other cases, the purpose of the process is to use the biochemical processes of the particular microbe to convert one material into other materials, such as when biomass is fermented for the production of industrial ethanol, butanol (butyl alcohol), and other compounds. Highly specific and bioengineered microbial cultures are often used to produce proteins and other biochemicals for pharmaceutical and medical research.

Background and History

It is impossible to say with any certainty when microbial fermentation began. It is certain, however, that the effects of yeast activity in producing wine and other alcoholic brews and in the baking of bread have been appreciated for thousands of years. The historical evidence indicates that beer and bread were staples of the ancient Egyptian diet and often served as wages. Bread loaves have been recovered from Egyptian tombs that are more than 5,000 years old, and the residues of beer found in Egyptian funerary vessels are equally old. Extant records of ancient Egyptian life show that beer and bread were part of every meal for young and old. Likely, using leavening agents (yeast) in baking and brewing activities was well-known before that time.

Ironically, knowledge of microbes themselves had to wait for the invention of the compound microscope in the end of the sixteenth century and the astute observations of Dutch scientist Antoni van Leeuwenhoek some seventy years afterward. The relationship between microbes and their observed effects, such as disease and fermentation, was not specifically identified for a further hundred years, when French microbiologistLouis Pasteur provided the first scientific explanations of the basis of fermentation and the brewing of beer. His work is believed to have set the stage for the modern science of biochemistry.

How It Works

Fermentation Processes. Zymology and zymurgy are the study and practice of fermentation and other microbial processes. Microbes are single-celled organisms such as yeast and bacteria. As living organisms, microbes have an active metabolism built on biochemistry. The various biochemical processes and reaction cycles that occur within living organisms function to extract energy for their continued existence through the conversion of materials that serve as foodstuffs. At the most fundamental level, simple sugars such as glucose and fructose are converted to carbon dioxide, water, and ethanol using yeast. The process is, in a sense, the opposite of photosynthesis, in which green plants convert carbon dioxide and water into glucose, and then into various other sugars and carbohydrates. The very same biochemical processes can be used to act on a variety of other substrate systems to produce different outcomes.

Bioengineering. On the other end of the scale are the procedures by which microbes with specific properties are produced. Because of their naturally high reproduction rates, microbes with different properties can be fairly readily identified, isolated, and grown in quantity. In addition, the development of genetic modification techniques allows them to be manipulated in ways that permit the enhancement of specific properties. In this way, yeast strains can be developed that are most suitable for specific varieties of wines and beers and for many other applications. Other microbes have been developed to have specific applications in the production of certain chemical compounds such as enzymes, proteins, and modified biochemicals. The use of microbial methods in the production of isolable chemicals is known as biosynthetic methodology.

Aerobic and Anaerobic Processes. Fermentation and other microbial processes can take place either in the presence of air (aerobic) or isolated from air (anaerobic). The products of the two processes are generally very different. Whereas anaerobic fermentation of a sugar solution produces carbon dioxide and ethanol, the same process carried out in the presence of oxygen will produce acetic acid rather than ethanol. This is what happens to fruit juice that is left out in the open for too long. Free yeast cells from the air settle into the liquid and begin aerobic fermentation, resulting in what is essentially a carbonated solution of flavored vinegar. The same fruit juice, fermented by the same yeast under anaerobic conditions, produces an alcoholic solution that becomes a fine-flavored wine.

Applications and Products

The main processes that rely on microbial action for their success are the brewing of beer, the fermentation of wine, and the baking of bread and other leavened baked goods. The brewing of beer and the fermentation of wine are, in principle, the same process. The differences between them consist primarily of the materials used to provide flavors and the order in which the resulting solutions are handled. At the heart of both is the same simple yeast-mediated fermentation of sugar and water to produce carbon dioxide and ethanol.

Wine. In the fermentation of wine, a mixture of fruit and fruit juice is prepared and added to an appropriate amount of water and allowed to stand for a short period of time to allow the various flavor components and colorings of the fruit to be extracted into the water. This stage is known as the must and is perhaps the single most important step in determining the final flavor and quality of the finished wine. In the next stage, the liquid is separated from the must and combined with the required amount of sugar and a mixture of nutrients needed for the proper growth of the yeast during fermentationmade up to volume with additional waterand then set to ferment in the airfree environment of a fermenter. The isolation of the solution during fermentation is usually achieved by the use of an air-trapping or bubbler system. This system prevents the influx of fresh air while allowing carbon dioxide produced during fermentation to escape from the fermenter.

This initial fermentation stage is followed by a series of decantations, in which the developing wine is separated from the yeast residues and reset to continue the fermentation process. Depending on the type of wine being produced, this may involve the addition of more sugar, other flavoring agents, and yeast of a different strain. The final stages of wine production involve clarification of the liquid, bottling, and storage (or cellaring) of the product so that it ages properly. During aging, a certain amount of fermentation may be desirable to produce a sparkling vintage, which is the procedure for the production of champagne-type wines. During the aging process, the various flavors of the wine meld and blend through various slow chemical reactions to produce the final distinctive flavor of the wine. The alcohol content of the wine produced in this way is typically about 12 to 15 percent.

Beer. The production of beer follows a similar procedure. A solution of sugar and water is prepared and blended with hops and malt, to which is added a robust yeast strain known as Saccharomyces cerevisiae, which reproduces quickly. Fermentation of beer takes place at a warmer temperature and at a more rapid rate than that of wine. This eliminates the need for an air-trapping system, as the production of carbon dioxide is so rapid that it continually displaces air that would enter the system. For small-batch brewing such as would be carried out by an individual at home, it is usually sufficient at this stage simply to cover the open vat with a sheet of cloth. The initial fermentation is typically complete in a very few days, after which the rate of fermentation slows considerably as the sugar content of the solution has been converted mainly to carbon dioxide. At this stage, a precisely controlled amount of sugar is added, and the solution is bottled and sealed. The minor fermentation subsequently forces the carbon dioxide into the solution, producing a beverage with an alcohol content of about 5 to 7 percent.

Sugars and Flavors. The type of sugar used in the production of beer and wine is not particularly relevant since the sugar that is fermented does not contribute to the flavor of the finished product, having been converted completely to carbon dioxide and ethanol. It is, therefore, of little consequence whether fermentation occurs using refined white sugar, liquid invert syrup, corn syrup, fructose, or glucose, sometimes referred to as corn sugar. On the other hand, sugars that are part of a flavored mixture, such as brown sugar or honey, will impart distinctive flavors to the final product. Mead, for example, is a type of wine made with honey in the fermentation and has a decidedly honeylike flavor. Similarly, brown sugar imparts a molasses flavor to the product because of the molasses content of the sugar.

Different varieties of grapes are used to produce the vast majority of wines. However, any vegetable substance can be subjected to fermentation to produce a corresponding wine, and wines made from different fruits are becoming ever more popular as consumers are more willing to try and accept other types of wines and wine flavors. Similarly, flavors that derive from materials other than the traditional hops and malt used in brewing beer are also becoming more acceptable, although the range of alternative substrates is more limited, being restricted primarily to wheat, barley, and other grains.

Bread.Bread and other leavened baked goods use yeast-mediated fermentation to produce carbon dioxide gas from sugar in the blend. The strain of yeast used in baking does not produce alcohol in the fermentation process. As the fermentation progresses within the dough, the gas collects and forms bubbles, but its escape is prevented by the elasticity of the dough. The bubbles of carbon dioxide gas act to expand the bulk of the dough, producing a light, fluffy baked good. The relatively hard outer crust forms as the carbon dioxide is driven out of the dough at the surface, which subsequently becomes toasted and caramelized, sealing in the remainder of the gases.

Other Foods. Many traditional foods rely on bacteria and microbial processes for their food value. Examples of those foods include such well-known concoctions as sauerkraut, kimchi, soy sauce, miso, black bean sauce, Worcestershire sauce, lutefisk, and all manner of yogurt. Yogurt, in particular, is marketed as a probiotic. The digestive tract, or gut, of the human body contains a wide but very specific variety of microbes whose presence is necessary for proper digestion and to maintain the inherent chemical balance of the digestive system. Probiotic foodstuffs are made to work with and promote the correctly balanced population of gut microbes, thus helping to maintain the optimum health of the host body.

Careers and Course Work

Career opportunities in zymology and zymurgy are numerous and becoming increasingly important as the economic value of zymology increases. The minimum requirement for pursuing a career in these fields is a solid grounding in biological and chemical sciences. Particular areas of study and specialization include microbiology, biochemistry, organic chemistry, physical chemistry, analytical chemistry, and genetics. One may also specialize in the brewing industry through a career in process technology, process operations, oenology (the study of winemaking), viticulture, distillery operations, mechanical engineering, and chemical engineering directed to applying bioprocessing and biosynthetic techniques.

Social Context and Future Prospects

Several aspects of zymology and zymurgy have become controversial, especially those that have led to the development of bioengineering, gene modification, and the use of mammalian cells as fermentogens for the production of specific proteins and enzymes. However, support is growing for the use of bioprocesses in solving many modern industry problems. For example, bioengineers are looking for microbes that can be used to alleviate pollution in different environmental situations. Particular interest is shown in microbes that can consume crude oil and other contaminants placed in the environment by accident or design. Others seek a microbial source of cheap but highly nutritious and acceptable food for human consumption. The potential for the development of specific microbes is essentially unlimited. Genetically engineering microbes allows them to serve specific functions, like drug delivery or treatment of a disease.

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