Biotechnology for Beginners

By Reinhard Renneberg

Biotechnology for Beginners, Third Edition presents the latest developments in the evolving field of biotechnology which has grown to such an extent over the past few years that increasing numbers of professional’s work in areas that are directly impacted by the science. This book offers an exciting and colorful overview of biotechnology for professionals and students in a wide array of the life sciences, including genetics, immunology, biochemistry, agronomy and animal science. This book will also appeals to lay readers who do not have a scientific background but are interested in an entertaining and informative introduction to the key aspects of biotechnology.

Authors Renneberg and Loroch discuss the opportunities and risks of individual technologies and provide historical data in easy-to-reference boxes, highlighting key topics. The book covers all major aspects of the field, from food biotechnology to enzymes, genetic engineering, viruses, antibodies, and vaccines, to environmental biotechnology, transgenic animals, analytical biotechnology, and the human genome.

• Covers the whole of biotechnology
• Presents an extremely accessible style, including lavish and humorous illustrations throughout
• Includes new chapters on CRISPR cas-9, COVID-19, the biotechnology of cancer, and more

• Language: English
• Publisher: Academic Press
• Release date: Jan 16, 2023
• ISBN: 9780323855709

Reinhard Renneberg

Reinhard Renneberg received his PhD at Central Institute of Molecular Biology, Berlin, German Democratic Republic in 1979. Since 1995 Professor Renneberg has been heading the Biosensor group at the Department of Chemistry of the Hong Kong University of Science and Technology. He is an expert in biotests, biosensors and signal amplification technologies. Dr. Renneberg is also the inventor of Cardiodetect, a rapid fatty acid-binding protein (FABP) immunotest which allows diagnosis or exclusion of acute myocardial infarction within half an hour after the onset of symptom and of InfectCheck, a barcode-style lateral flow assay for semi-quantitative detection of C-reactive protein (CRP) in distinguishing between bacterial and viral infections. Dr. Renneberg is the author of several books on biotechnology, including the award-winning textbook Biotechnology for Beginners which the university includes in many of its training packages. He advises a wide range of biotechnology companies as expert content provider, pedagogical expert and top-level academic relay for biotechnology education.

Book preview

Chapter 1: Beer, Bread, and Cheese

The Tasty Side of Biotechnology

Abstract

Biotechnology sounds like something new, less than a hundred years old. It isn’t; it is probably as old as agriculture, dating back to at least 8,000 BC. And it all started with fermentation, a set of chemical reactions carried out by microorganisms to break down glucose to obtain usable energy. Chief among these microorganisms are yeasts that can transform glucose into ethanol in the absence of oxygen, a process called glycolysis, or into carbon dioxide in the presence of oxygen, a process called respiration. These two different lifestyles have made yeast an indispensable companion of every culture or civilization producing bread or alcoholic beverages. But, yeasts tell only part of the long story of biotechnology: much smaller microorganisms, bacteria, have also been helping humans transform, enhance, and preserve foods. Cheese, tea, coffee, and many other popular foods are all fermentation products. Biotechnology started by being delicious.

Keywords

Fermentation; Brewing; Ethanol; Beer; Bread; Cheese; Yeast; Bacteria; Glycolysis; Respiration

1.1In the Beginning, There Was Beer and Wine—Nurturing Civilization

1.2Yeasts—The Secret Behind Alcoholic Fermentation

1.3Now as Ever, Beer Is Brewed From Yeast, Water, Malt, and Hops

1.4Cells Work on Solar Energy

1.5For Yeast, Alcohol Has Nothing to Do With Enjoyment, But All With Survival

1.6Highly Concentrated Alcohol Is Obtained by Distillation

1.7Bacterially Produced Acidic Preservatives

1.8Coffee, Cocoa, Vanilla, Tobacco—Fermentation for Enhanced Pleasure

1.9An Alliance of Molds and Bacteria in Cheese Production

1.10Sake and Soy Sauce

1.11What Exactly Is Fermentation?

Cited and Recommended Literature

Useful Weblinks

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WHAT WOULD YOU LIKE TO DO BETTER

IF YOU COULD START ALL OVER AGAIN?

THAT’S EASY TO ANSWER.

I WOULD TAKE TEACHING

AT LEAST AS SERIOUSLY AS RESEARCH.

TEACHING IN MY VIEW

IS NOT JUST THE PRESENTATION OF FACTS,

BUT PASSING ON MY EXPERIENCE AS A SCIENTIST

AND MY PERSONAL VIEWS ABOUT SCIENCE,

THE WORLD AND US HUMANS.

THE WEAPON OF SCIENCE

IS ITS APPETITE FOR KNOWLEDGE,

BUT IT IS A BLUNT WEAPON

IF USED WITHOUT A SHARP INTELLECT,

AND EVEN THE SHARPEST INTELLECT

LACKS VIGOR WITHOUT PASSION AND COURAGE.

THESE, IN TURN, ARE SHORT-LIVED

IF NOT SUSTAINED BY THE POWER OF PATIENCE.

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Gottfried Schatz (1936–2015, Professor for Biochemistry, Basel)

1.1: In the Beginning, There Was Beer and Wine—Nurturing Civilization

The first beer we know of was brewed by the Sumerians who lived in Mesopotamia between the rivers Euphrates and Tigris (modern-day Iraq), in 8,000–6,000 BC. They produced a nutritious, nonperishable, and intoxicating beverage by soaking barley or Emmer wheat (an ancient wheat cultivar grown in the region) in water and letting it germinate. The process of husking wheat around 3,000 BC is shown on a Sumerian clay tablet, known as Monument bleu, in the Louvre museum in Paris. The germinated grain was then kneaded into beer bread, which was only lightly baked and then crumbled and stirred into water. The mixture was later poured through a wicker sieve and kept in sealed clay vessels. Soon, gas bubbles began to rise as fermentation set in.

Fermentation is an anaerobic process in which the sweet juices are transformed into an alcoholic drink—in this case, beer.

Part of the germinated grain was dried in the sun—a process equivalent to modern kiln drying—to preserve it for periods when fresh grain was in short supply. The beer brewed later by the Babylonians in the same region had a slightly sour taste, due to lactic acid fermentation taking place simultaneously. Lactic acid fermentation helped greatly to prolong the storage life of beer, as many microbes cannot survive in an acidic environment. This was immensely important in the hot climate of the Middle East where hygienically safe beverages were at a premium.

Alcohol is fermented sugar, a final metabolite of yeast. Even an alcohol content of 2–3% affects the permeability of the cytoplasmic membrane in bacteria and inhibits their growth. In the hot climate of the Middle East, slowing down the growth of microbes through fermentation is a definite—perhaps even decisive—advantage. The development of agriculture brought about a dramatic rise in population, and with it a dearth of clean drinking water. It is a problem that the Western world had also been struggling with right to the end of the 19th century, and which many other parts of the world are still facing. Think of the familiar images of the river Ganges where animal and human carcasses and feces pollute the drinking water. Contaminated water can be highly dangerous, whereas fermented products such as beer, wine, or vinegar are virtually germ-free. They could even be used to make slightly contaminated water safe, as not only alcohol, but also organic acids in the fermented products inhibit the growth of potential pathogens.

The thirst of our ancestors was quenched by beer, wine, or vinegar rather than water. The oldest biotechnology in the world provided safe and stimulating drinks that nurtured civilization. Such revolutionary technology was bound to succeed.

Not only the people of Mesopotamia, but also the ancient Egyptians were beer brewers. A mural dating from around 2,400 BC shows the production process.

The Egyptians were already aware that using the sediment from a successful batch would speed up the new fermentation process. Their beers tended to be dark, as they used roasted beer bread, and they reached an alcohol content of 12–15% (Figs. 1.1 and 1.2). Bottled beer was also an Egyptian invention. When the pyramids were built, beer in clay bottles was delivered to the building site.

Fig. 1.1

Fig. 1.1 Beer preparation 4,400 years ago.

Fig. 1.2

Fig. 1.2 Boeotian women from ancient Greece baking bread 6,000 years ago.

While the Celtic and Germanic tribes were happy with mead, a sour-tasting beer stored in vessels in the ground holding up to 500 L (132 US gallons) at a temperature of around 10°C (50°F), the art of beer brewing reached another heyday when it was developed by monks in the 6th century AD. Their motivation lay in their fasting rules—liquida non fragunt ieunum (liquids do not break the fast)—was the motto that led them to brew strong beers with a high alcohol content.

The word beer itself is supposed to be derived from the ancient Saxon word bere. meaning barley. Being able to brew good beer is one thing—knowing how it happens is quite another.

The first person to spot the yellow yeast blobs in a beer sample (Fig. 1.3) through his single-lens microscope was Antonie van Leeuwenhoek (1632–1723, Box 1.1), who had also been the first person to see bacteria (Box 1.2).

Fig. 1.3

Fig. 1.3 Yeast, as drawn by Leeuwenhoek (above) and seen under a modern-day scanning electron microscope, clearly showing the budding daughter cells.

Box 1.1

Biotech History: Leeuwenhoek

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Antonie van Leeuwenhoek working with his single-lens microscope, capable of 200  × magnification.

"What we saw was vigorous and rapid movement, similar to that of a pike through water. The creatures were low in number. A second species, looking like Fig. B, frequently spun round themselves like spinning tops and finally began to move as shown in Figs. C and D. These were more common. A third species did not seem to have a defined shape—they seemed to be oval-shaped, but then again, they looked like circles. They were so small—no larger than what you see in Fig. E—while moving amongst themselves like a swarm of flies or midges.

They were so numerous that I thought there were several thousands of them in the water (or in water mixed with spittle). The sample—which I had scraped out between my canines and molar—was no larger than a grain of sand. It mainly consisted of slimy masses of different lengths, but the same thickness. Some were curved, others straight, as in Fig. F, in no particular order."

Source: Paul de Kruif, Microbe Hunters (1930).

This description of a view of the deposit on his teeth under the microscope opened a whole new world to humankind. Leeuwenhoek (1632–1723) was a merchant and self-taught scientist. He was the first person to see bacteria and draw them. It all began when he watched a spectacle maker grind lenses at a fair and learned how to do it himself. It became an obsession, and he began to make ever stronger glass lenses, building microscopes with up to 200  × magnification. He could spend hours watching a hair from a sheep that looked like a strong rope under his single-lens microscope.

One day, Leeuwenhoek hit on the idea of looking at a drop of water from his rain barrel and had the most terrible shock when he saw it under the microscope. It was teaming with tiny creatures, swimming about as if playing with each other. Leeuwenhoek estimated their size was a thousandth of the eye of a louse.

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Leeuwenhoek’s first drawings of bacteria. The British science writer Brian F. Ford tried out one of Leeuwenhoek’s microscopes and discovered that he was able to see spirilli.

Encouraged by a friend, Leeuwenhoek wrote an enthusiastic letter in Dutch to what was then the most prestigious organization of scientists, the Royal Society of London, in 1673. The learned gentlemen were most surprised to read a description of miserable wee beasties, as Leeuwenhoek chose to call them in his letter.

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Leeuwenhoek’s microscope. He built around 500 single-lens microscopes.

Robert Hooke (1635–1703) was a member of the Royal Society at the time and was in charge of organizing new experiments for every meeting of the society. When looking at slices of cork through his own multilens microscope, he discovered a regular pattern of small holes which he named cells. Hooke also built a microscope to Leeuwenhoek’s specifications and was able to confirm the Dutchman’s observations. Little did he know that the wee beasties also consisted of cells, in most cases just one single cell.

The scientists of the Royal Society saw with their own eyes that microscopic creatures existed and became very excited about them. Leeuwenhoek, who had never attended a university, was unanimously voted in as a member of the Royal Society in 1680.

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Robert Hooke’s multilens microscope under which he examined thin sections of cork, which he described in terms of cells.

Through his dexterity, curiosity, and persistence, he had achieved more than many of his academic contemporaries who, when asked about the number of teeth a donkey had in its mouth, would much rather look it up in Aristotle’s writings than look into a donkey’s mouth.

Kings, princes, and scientists of all countries were interested in Leeuwenhoek’s discoveries. The Queen of England and King Frederic I of Prussia, as well as the Russian Czar Peter the Great (who had come to the Netherlands incognito to study the art of shipbuilding), all came and paid him a visit.

The beasties were a fascinating novelty for a while, but then were forgotten again.

Box 1.2

Essential Biomolecules and Structures

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Hydrogen (H), oxygen (O), carbon (C), and nitrogen (N) make up 96% of the human body mass. Alongside helium and neon, they are the most common elements in the universe. Sulfur (S)—important for the structure of proteins—and phosphorus (P)—important for energy conversion and signal control—occur in far smaller proportions.

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Nucleotides are the building blocks of nucleic acids (DNA and RNA), the information carriers within cells. They consist of a monosaccharide (deoxyribose or ribose), a base (adenine (A), guanine (G), cytosine (C), and thymine (T); in RNA, uracil (U) replaces thymine) and a phosphate residue. A and T (shown here) form two H bridges while G and C form three.

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Cofactor adenosine triphosphate (ATP) is the universal energy storage medium, consisting of an adenine residue, a ribose, and three phosphate groups. Hydrolysis leads to the formation of ADP and phosphate and the release of energy.

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Lipids (fats) are insoluble in water, but dissolve well in organic solvents. This applies to membrane lipids (phospholipids, glycolipids, and cholesterol) and storage lipids (fats and oils). Shown here is a phospholipid consisting of a hydrophilic head (glycerol and phosphate) and hydrophobic tails (fatty acids).

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Carbohydrates (sugars) provide energy (glucose, starch, and glycogen) and structural compounds (cellulose and chitin). They are composed of ketones (with—C  =  O group) and aldehydes (with HC  =  O) with two or more hydroxyl groups (-OH). The monosaccharide β-d-glucose (dextrose) is shown here.

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Twenty different amino acids are linearly linked to form a polypeptide. They have a central C atom around which an amino group (-NH2), a carboxyl group (-COOH), an H atom, and a variable side chain (-R) are arranged.

How to visualize a molecule

The models that come closest to reality are calotte models that recreate the dimensions and spatial arrangement of the atoms, their van der Waals radii demarcating the territory they occupy.

Ball-and-stick models, by contrast, represent atoms as balls of equal size that are interconnected with sticks.

Structural formulae take a minimalist approach, representing bonds as one or several lines between the element symbols. R (residue) often stands for a large proportion of a molecule that was not included for the sake of simplicity.

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Starch is a polysaccharide consisting of thousands of β-d-glucose units linked together via glycosidic linkages.

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DNA, the double helix. The illustration shows how RNA polymerase unwinds DNA to form mRNA as well as some transcription proteins and DNA polymerase (more detail in Chapter 6).

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Membrane receptors transduce signals from the extracellular to the intracellular space. Shown here is a cascade of smell receptors. Coupled with G proteins and adenylate cyclase, they are responsible for the opening and closing of ion channels. In addition, there is a vast number of intracellular receptors (more detail in Chapter 5).

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Enzymes are biocatalytic proteins. Shown here is glucose oxidase (GOD), which is a dimer molecule consisting of 2 × 256 amino-acid components. FAD (flavin adenine dinucleotide) acts as a prosthetic group in the active center (more detail in Chapter 3).

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Antibodies are proteins with a crucial role in the immune system. Shown here is the Y-shaped immunoglobulin G, which consists of two light (220 amino acids each) and two heavy chains (440 amino acids each) resembling two arms plus fingertips and a foot. The arms and fingertips are the antigen-binding sites (paratopes) (more detail in Chapter 4).

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Box 1.3

The Protein Database Molecular Machinery—Interactive Website

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In those days, yeast was available in concentrated and purified form and used for baking, brewing, and winemaking (Fig. 1.4).

Fig. 1.4

Fig. 1.4 Medieval beer brewing.

Fig. 1.5

Fig. 1.5 Beer brewing in Ancient Egypt.

Fig. 1.6

Fig. 1.6 Beer—the carbon dioxide bubbles are clearly visible.

Fig. 1.7

Fig. 1.7 The Netherlands issued 10 nondenominated 1 stamps in 2011 to mark the 75th anniversary of the Netherlands’ Society for Microbiology. The various microscopic life forms harnessed by humans featured on the stamps include yeast (S. cerevisiae) for fermentation in wine production, lactic bacterium (Lactococcus lactis) for making cheese from milk, Rhizobium that provides nitrogen for planting, Anammox (short for ANaerobic AMMonium OXidation) bacteria for rendering wastewater harmless, a bacteriophage that kills harmful bacteria, Penicillium for production of penicillin, Methanosarcina for the production of methane gas (biogas), marine green algae, Tetraselmis suecica, for the production of biodiesel, A. niger (black mold) for breaking down vegetable waste into compost, and Bacillus bacteria that repair concrete by filling up cracks with lime.

Fig. 1.8

Fig. 1.8 Bacteria. Bacteria are prokaryotes , i.e., their genetic information is not contained in a nucleus, but is found in the cytoplasm—mostly as double-stranded DNA loops. They are lacking organelles typically found in eukaryotic (yeast, mold, higher animal, and plant) cells, such as mitochondria (for respiration) or chloroplasts (for photosynthesis), and an endoplasmic reticulum. Most bacteria are heterotrophic, i.e., they draw their energy from organic matter, whereas other species get their energy through photosynthesis or from inorganic (e.g., sulfur) compounds. Bacteria comprise mobile as well as immobile single-celled organisms (e.g., rods and cocci), but also as multicellular filaments on the substrate, as in Nocardia and the fungus-like structures (mycelia) of Streptomyces spp. in the air. The color tables show biotechnologically relevant bacterial species. The structure of bacterial cell walls may vary (see Chapter 4 ). According to their ability to take up a stain that makes them visible under the microscope, bacteria are divided into Gram-positive and Gram-negative species. Gram-negative aerobic rods and cocci include Pseudomonas spp. (utilization of hydrocarbons, steroid oxidation) and Acetobacter (production of acetic acid), Rhizobium (nitrogen fixation), and Methylophilus (single-cell protein, methanol oxidation). By contrast, the intestinal bacterium Escherichia coli, the microbial equivalent of guinea pigs in research, are also Gram-negative rods, but facultatively anaerobic . Bacillus (enzyme production) and Clostridium (acetone and butanol production) spp. are spore-forming rods and cocci . Club-shaped Gram-positive Corynebacterium spp. produce amino acids. Lactic acid-producing Streptococcus spp., Staphylococcus (food poisoning), Propionibacterium (vitamin B 12 , cheese production), Nocardia spp. (hydrocarbon oxidation), and Streptomyces (antibiotics and enzymes) are all Gram positive. Lactobacillus spp. (lactic acid-producing) are Gram-positive, nonspore-forming bacteria. While some bacteria are able to cause serious damage through disease and food spoilage, others have large economic potential in biotechnological processes.

1.2: Yeasts—The Secret Behind Alcoholic Fermentation

Yeasts are members of the largest and most varied phylum of fungi—Ascomycota.

Unlike bacteria, which are prokaryotes, yeasts have a complex eukaryotic cell structure, including a genuine nucleus and compartments such as mitochondria. They have also been called budding fungi in reference to their asexual propagation. Yeasts, however, can also multiply through sexual reproduction, i.e., through the copulation of two haploid budding cells, each of which contains a complete set of chromosomes. Yeasts are classified on the basis of their mode of reproduction (Fig. 1.9).

Fig. 1.9

Fig. 1.9 Fungi. Fungi have an eminent role to play in the natural cycle, particularly in degradation processes. To date, around 70,000 fungal species have been classified. Yeasts , like the fungi, are eukaryotes with nuclei that contain all genetic information ( Fig. 1.9 ). Yeasts are sprouting fungi ( Endomycota ). We distinguish wild yeasts from cultured yeasts grown at an industrial scale, such as brewers’ yeast (e.g., Saccharomyces carlsbergensis), wine and bakers’ yeast (Saccharomyces cerevisiae), or fodder yeast (Candida). Candida utilis is grown on the sulfite-containing effluents of paper mills. Candida maltosa feeds on alkanes (paraffins) of crude oil, producing fodder protein. Trichosporon cutaneum degrades phenol in effluents that would be toxic to other fungi. The yeast Arxula adeninivorans is used in microbial effluent sensors (see Chapters 6 and 10 ). Molds are members of the largest group of fungi, Ascomycota , comprising 20,000 different fungi. Unlike the spherical yeasts, their cells are long and thin, and most of them are strictly aerobic. Mold spores are formed asexually by the division of the cell nuclei in the mycelia. These mycelia extend into the air and are called sporangia. The mature spores travel easily in the air, and when they land on a suitable substrate, they germinate to form new mycelia. Ascomycota are further subdivided according to the morphology and color of asci. Their mycelia all look pretty much the same—a tangle of thread-like hyphae. Many of the industrially cultured fungi are grown in submerged cultures in tanks, where they produce clumps of mycelia but no spores. They require nutrients similar to those of yeast but are more versatile. Unlike yeasts, some of them can thrive on cellulose (Trichoderma reesei) or lignin (Phanaerochaete chrysosporium) (see Chapter 6 ). Fungi of the Aspergillus and Penicillium genera are used in fermentation, especially in the enzymatic degradation of starch and protein in barley, rice, and soybeans, while Aspergillus niger produces citric acid. Penicillin is obtained from Penicillium chrysogenum (see Chapter 4 ). Other Penicillium species are used in the production of certain types of cheese, such as Camembert or Roquefort. Amylases and proteases produced by fungi are also harvested for industrial enzyme preparations (see Chapter 2 ). Endomycopsis and Mucor also produce industrial enzymes, while Fusarium species are used to obtain protein for human consumption (see Quorn, Chapter 6 ).

Pasteurizing

It was Louis Pasteur who discovered that heating up wine very briefly was enough to kill off any bacteria that might spoil it. The method was also suitable for preventing milk from turning sour.

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In honor of its inventor, the process that kills off most microorganisms present in a product was named pasteurization. Even raw milk produced to high hygienic standards contains 250,000–500,000 microbes per mL (cm³). Milk sold in supermarkets is therefore usually briefly heated to between 160°F and 165°F (71°C and 74°C), i.e., it is pasteurized, killing off 98–99.5% of microorganisms contained in it. UHT (ultra-high temperature) milk, which can keep for weeks without refrigeration, has been briefly heated over steam to 248°F (120°C) and it is then filled into pasteurized containers.

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Bacterial colony pattern formation.

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Pseudomonas.

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Aspergillus niger on agar.

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Penicillin-producing mold (Penicillium notatum).

Yeasts are single-celled organisms, also called mother cells. Each of them sprouts several buds which grow into viable daughter cells. These are then pinched off and can, in turn, form new cells (Fig. 1.3). They are heterotrophic, i.e., they depend on organic nutrients and cannot perform photosynthesis, preferring an acidic environment in their hosts. Their cell walls contain a substance otherwise found in insect skeletons—chitin—as well as hemicellulose. The alcoholic fermentation process in beer production depends on the carbohydrates in the grain. These are mainly polysaccharides and they can only be digested by the glycolytic enzymes in the yeast cells (Fig. 1.15) if they are first broken up into disaccharides and monosaccharides.

1.3: Now as Ever, Beer Is Brewed From Yeast, Water, Malt, and Hops

As in Sumerian times, germinating barley stands at the beginning of the brewing process since the germination process turns barley into malt by enhancing the production of certain enzymes (Box 1.4).

Box 1.4

Modern Beer Brewing

Beer brewing is most straightforward in Germany because it must comply with the purity requirements established in Bavaria in 1516 (see p. 31), i.e., it must not contain anything other than barley malt, hops, and water, and it must be prepared with yeast.

The starch contained in grain cannot be fermented straightaway but must first be broken down by enzymes (amylases). These develop while the grain is left to germinate. In a process known as saccharification, they break down starch into maltose and glucose. Malting is the first step in beer brewing, followed by the preparation of wort and fermentation.

In the malting house, barley is sorted and cleaned and left to soak in water for up to 2 days. The grain is then transferred to large germinating trays, where it remains for 7 days at a temperature of 59–64°F (15–18°C). The grain is turned automatically during this period. The germination process is then brought to a halt.

In the resulting green malt, the starch has only been broken down partially into maltose. The malt is now kiln-dried at slowly rising temperatures (initially 113°F/45°C), then rising to 140–176°F (60–80°C) and—for dark beer—up to 221°F (105°C). The result is called brown malt.

In the brewhouse, wort is prepared by mashing the shredded malt. Large quantities of water are stirred in, and the mixture is heated. The mashing process is interrupted at scheduled intervals or steps for enzymatic breakdown to take its course. Below 50°C, β-glucanases degrade gum-like substances that obstruct filtration.

The protein breakdown step is scheduled at 122–140°F (50–60°C), and the saccharification step is reached at 140–165°F (60–74°C), where starch-cleaving enzymes (α- and β-amylases) break down the remaining starch into glucose, maltose, and larger starch molecule fragments (dextrins).

Once the mash has settled at the bottom of a lauter tun or the clear liquid has been strained through a mash filter, it is boiled, and hops are added to produce concentrated and germ-free wort.

Hops contain bitter substances as well as resins and essential oils, which all contribute to a fresh, bitter taste and better storability.

When the wort has cooled and taken up oxygen in a whirlpool, pitching yeast is added. These yeasts are pure cultures of Saccharomyces cerevisiae, which are first encouraged to grow by the increased oxygen supply and then transferred to a fermenter.

Lager beers are the result of slow, bottom fermentation (8–10 days). The German word Lager means storage, and indeed, these beers store very well and are very stable when shipped.

The faster top fermentation (4–6 days) produces weissbier, ale, porter, and stout.

The beer is then left to mature in storage tanks over several weeks at a temperature of 32–35.6°F (0–2°C) before it is transferred into small kegs or bottles.

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The malt is then crushed, mixed with warm water, and filled into mash tuns. Within a few hours, the starch stored in the grain is broken down into maltose, glucose, and various other sugars by virtue of enzymes called amylases.

Other enzymes (β-cellulases) break down the outer layers of the barley grain, thus making the starch inside available to α-amylase. In a next step, the solid components of the mash are filtered out and the sweet liquid transferred to the copper tanks (coppers) where hops are added. Hops give the mixture a bitter taste.

The mixture is now called wort and is poured into a fermentation vessel. Brewers’ yeast is added to set off the fermentation process (Figs. 1.10–1.12).

Fig. 1.10

Fig. 1.10 True-to-scale reproduction of biotechnologically relevant microorganisms. The length of a Paramecium is roughly equivalent to the diameter of a human hair—one-tenth of a millimeter or 100 μm.

Fig. 1.11

Fig. 1.11 Right: Size ratio of eukaryotic and prokaryotic cells and viruses.

Fig. 1.12

Fig. 1.12 Far right: A bacterial cell (Escherichia coli) in numbers. There are 5 × 10 ³⁰ bacteria on Earth; 50% of all living matter is bacterial.

Once the alcoholic fermentation process is completed, the beer is allowed to mature in large tanks. Eventually, the beer is briefly heated to kill off any noxious microbes and it is then filled into bottles, cans, or kegs.

While the basic processes in beer brewing have remained virtually the same for thousands of years, our knowledge has expanded. Our ancestors were unaware of the fact that they were harnessing microbes for their purposes.

Discoveries similar to those of the Sumerians were made by people all over the world. Winemaking probably developed 6,000 years ago in the Mount Ararat region. However, recent findings point to the Chinese as the first winemakers—9,000 years ago (Box 1.10).

Box 1.10

Deciphering the Vintage Code

Patrick McGovern of the University of Pennsylvania has a dream job—he combines chemical analysis with archeology, analyzing traces of wine in ancient vessels. His claim to fame was the discovery of the purple imperial dye obtained from the mollusk Murex trunculus. This was followed by McGovern’s Noah hypothesis: As described in the Bible, Noah landed on Mount Ararat in Eastern Turkey and he soon started growing vines there. It seems that that area is the cradle of agriculture where einkorn wheat was grown for the first time.

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Chinese wine vessel and Prof. McGovern tasting historic wine samples.

McGovern began by comparing the DNA of wild vines (Vitis vinifera sylvestris) (see Chapter 10), which is found between Spain and Central Asia. It is the ancestor of the cultured vine varieties. He is now exploring the Turkish Taurus mountains where the river Tigris rises, hoping to find the original wild vine. José Voulilamoz at the Italian Instituto Agrario di San Michele all’Adige in Trento and Ali Ergül at Ankara University are part of the DNA team. Every type of grape they can lay their hands on in the region is being collected in order to trace back the origins of