INTRODUCTION TO THE BREWING PROCESS

Laisy Almanza
Pre-Med Student at USFSP
Due: July 25^th, 2014

Even though beer was brewed from the earliest colonialtimes the lager style of beer was widely introduced by German immigrants and due to the lighter color and flavor profile became the dominant American choice by the mid 19th century and for this reason most people believe that beer started in Germany (Murray, 2009). The number of small specialty brewers in the U.S. has augmented dramatically since 1980. This sea change is linked to President Jimmy Carter’s signing, in 1976, of legislation allowing home brewing, though it is still illegal in some states and In 1997 the number of U.S. breweries exceeded that of Germany. Surprisingly craft beer has become a five billion dollar annual market (Murray, 2009). The majority of people who drink beer think of it as a simple alcoholic beverage they buy at the liquor store to enjoy at any gathering with family, friends, or both. However, they usually don’t stop and think about how it is made or how long it may take to make each batch especially in a microbrewery. Many also don’t stop and consider the microbiology, chemistry, and the scientific steps involved in the entire process of brewing or how important quality assurance is throughout each step. Each batch made is analyzed thoroughly so that it not only tastes its best but also has nothing that should not be there. Every aspect of the beer is observed and measured from the alcohol content to bitterness and even the pH and oxygen content. It is an extremely complex process but it can be simplified so that people who truly enjoy their beer can understand the method behind it. Only true beer lovers will enjoy understanding the difference between the color, taste, smell, etc. of each particular beer and once they know the difference they will be able to differentiate between a truly good beer and it probably won’t be the one they always considered the best. Brewers take their jobs very serious and really attempt to make the best product. Some brewers choose to not send their product overseas simply because of its shelf life, or how long it takes for it to loose it’s special characteristics, and its quality even though this may mean a loss of income and expansion. Beer is made from four crucial ingredients: water (90% of beer is water), fermentable sugars (malted barley), hops and yeast. With the right settings, the yeast will ferment the fermentable sugars to alcohol, carbon dioxide and the taste we know as beer. Once the beer is bottled it can be aged anywhere from a week to 3 months depending on the style of beer the brewer wants to make. Of course there are other optional ingredients that can be added to the beer to make it unique such as sugars (white or brown), syrups, honey, other sweeteners, fruits, vegetables, grains, herbs and spices, and many others like chocolate or coffee.

Malted barley is a naturally processed form of barley, which is a grain similar to wheat in appearance. A “maltster” will steep the barley in water until it begins to sprout under certain conditions. The germinated barley is then dried and once the drying is complete the barley is officially malted. During this procedure, sugars, soluble starches and characteristics in the barley desirable for brewing beer are developed. The malt is mostly converted to sugars through a process called mashing where the malt is submerged in water at precise temperatures that allow enzymes in the barley to convert starches to sugars. These sugars are converted to alcohol, carbon dioxide and the flavor of beer through fermentation as stated before. The liquid extracted from the mashing process is known as wort. Some brewers choose to substitute corn, rice, wheat, rye, or other grains for a portion of the malt because although the fermentable sugars created from the starches of these grains will ferment through the same process as the malt sugars do, they will add their individual fermented character to the beer. This is used mostly to lighten the taste of the beer (Briggs, 1971).

For home brewers there are malt extracts available so that they do not have to go through the process of malting the barley or even mashing the grains. The malt extract is malted barley that has been processed into a sweet malt soup. Then, depending on if the brewer wants moist or dry malt, 70-80 percent of the water is evaporated to give a concentrated syrup or all of the water is evaporated to give a dry powder. There are also many malt extracts and home-brew kits that have different hop flavors so that the home brewer can add that floral taste unique to hops just as breweries do to their beer. All that would need to be done by the home brewer is to add water and yeast, which is sometimes also provided in the kits (Papazian, 2003).

As hops are considered primarily as a flavour ingredient for beer, with the added benefit of having anti-microbial effects, hop research is focused on hops as a bittering agent, as an aroma contributor and as a preservative (Schönberger & Kostelecky, 2011). Hops have been used in making beer for approximately 200 years (Filmer, 1982). It is important to remember that hops are conelike flowers of the hop vine and because of this add a floral aroma along with their bitterness. Unfortunately, because of this same reason they are perishable (Lewis & Young, 1995). The sweetness of malts is balanced by the hop’s bitterness. Hops can also extend the life of the beer and can improve head retention, which is why brewers consider hops extremely important. It is important to understand the biochemistry of hops and how it can interact with the beer making process. Hop's produce Lupulin glands, which are tiny capsules containing resins and oils that become the major contributing factors through the brewing process. The hop oils provide the floral flavor and smell while the resins add to the bitterness of the beer. Hop oils should be used scarcely and can be added at many stages of the brewing process either at the end of boiling, during or after fermentation or even just before packaging (Lewis & Young, 1995).

Even though it may seem unimportant, the water you use for making beer is also very important especially for home brewers because it will add its character to the beer as well. It is important to make sure that the water tastes good and that it does not contain any excess chemicals or minerals because they will change the taste of the beer. It is also important to use potable water in breweries so that the microbial growth can be minimal.

In my opinion the most important ingredient in the brewing process is the yeast. Yeast is responsible for converting the bittersweet “tea” made from the fermentable sugars and the hops to the alcoholic beverage known as beer. Yeasts are living microorganisms that use sugar as food for their life cycle. Yeast can grow aerobically (respiration) or anaerobically (fermentation) but only the anaerobic process is used in beer production. Unfortunately, even though there are thousands of unique yeasts in the world, most of them are wild yeasts, which will result in the production of some very unique brews that aren’t always very delightful to taste. Wild yeasts not only cause odd savors but also overflowing, over carbonation, haze development and all kinds of indescribable fermentation features. In general there are two types of yeast used in brewing. These are lager yeast and ale yeast. Lager yeasts ferment at cooler temperatures and generally yield a much cleaner tasting beer with fewer esters while ale yeasts tend to yield a beer with fruitier esters. There is much more diversity among ale yeasts than lager yeasts. Ale yeasts (Saccharomyces cerevisiae) are said to be “top-fermenters” because during the beginning of fermentation period they tend to flocculate on the surface of the beer while lager yeasts (Saccharomyces carlsbergensis) are said to be “bottom-fermenters” because they flocculate and sediment at the bottom of the tank. Both of the yeasts are broken down again into groups of strains (Papazian, 2003).

The cooled wort obtained from mashing of the malted barley is fermented by yeast to make an immature beer also known as green beer. The main fermentation, in which this green beer along with the yeast is produced, is followed by a slower process at a lower temperature and with less yeast also known as secondary fermentation or maturation. Secondary fermentation is the process of keeping green beer in contact with yeast after the primary fermentation has ended. For the yeast to live and grow successfully the wort must contain sufficient amount of nutrients. Yeasts need very specific conditions and nutrients to be able to flourish as needed to for the brewing process. For example, they need fermentable carbohydrates, assimilable nitrogen, molecular oxygen, biotin, sources of phosphorus and sulfur, calcium and magnesium ions and trace elements such as copper and zinc ions. Some worts can be enhanced by adding certain trace elements or other nutrients needed for the yeast to grow successfully. Another important parameter for the wort is the dissolved oxygen content because the molecular oxygen requirement is different for certain yeasts. Enough molecular oxygen has to be supplied at the beginning of fermentation but once this is done then no more is needed and anaerobic conditions are established and essential to prevent detrimental oxidation reactions that can spoil the beer. The quantity of oxygen is inversely proportional to the specific gravity as well as the temperature. Too much oxygen results in too vigorous fermentation and excessive yeast growth and too little cause accelerated loss in yeast vitality and viability.  Even on wort, yeast must be induced to produce the maximum amount of alcohol and have the minimum amount of growth. This is done by restricting the availability of oxygen and using lower fermentation temperature than those preferred by the organism.

As stated earlier secondary fermentation involves keeping the green beer in contact with the yeast after primary fermentation in ended. An advantage of doing this is that any oxygen which gains access will be absorbed instantaneously by the microbe. Once the yeast is removed then the brewer must be careful and make sure that oxygen does not enter and touch the product. Maturation most often involves the gradual lowering of the temperature and giving enough time so that the yeast can settle out or flocculate and chill haze particles can form. This waiting period is called lagering or aging as mentioned earlier. This process can be expansive and many brewers rather accelerate this process.  Brewers can accelerate the formation, prevent the formation, or accelerate the removal of the chill haze that usually forms during maturation. The formation of these particles is catalyzed by molecular oxygen and controlling it can help accelerate its formation or simply stop its production.

Once pitched into wort, yeast uses the nutrients in the wort to provide energy (ATP) and in the process produces alcohol and carbon dioxide. This process also produces reducing power (NADPH) for the synthesis of new yeast substance. The nutrients can also be directly assimilated into new cell components or used to generate intermediates for this process. In addition, these energies lead to the synthesis and secretion into the work of a large number of minor metabolic products, which can add special features savors and scents (Lewis & Young, 1995).

The production of beer includes not only fermentation but glycolysis as well. It is extremely important to understand all biochemical pathways involved in brewing so that the complexity of the beer making process can be appreciated. First of all a biochemical pathway is recognized as a serious of reactions, each mediated by an enzyme in which the product of one reaction becomes the substrate of the next. Pathways whose purpose is to make energy chemically oxidize their substrates normally achieved by transferring a hydride ion to an enzyme cofactor. This oxidized cofactor NAD⁺ is converted to NADH (reduced form). Dehydrogenase enzymes conduct the oxidation-reduction reactions. Because energy is released through oxidation, the reaction is controlled so that some of the energy released is held by the cell in the form of ATP (adenosine triphosphate).

ADP + inorganic phosphate (P_i ) à ATP

The reaction above consumes energy and is driven by high-energy compounds formed during metabolism and the inverse reaction (hydrolysis of ATP) releases energy which can be used to synthesize new products. The source of the heat rising during fermentation of the wort comes from the fact that energy transfer reactions are never 100% effective and waste energy is always dispersed. Usually sufficient waste heat is formed to increase the temperature of a lagged vessel about 17°C and this heat must be removed by cooling. Glycolysis (figure 1), which is an important pathway in the brewing process, is said to be amphibolic. This means that it can have both catabolic and anabolic functions.

 

Figure 1. Simplified Process of Glycolysis

 

The fermentable sugars in brewer’s wort are maltose, maltotriose and smaller amounts of sucrose glucose and fructose. The trisaccharides are transported into the cell and hydrolyzed to glucose while sucrose is hydrolyzed outside the cell to glucose and fructose then transported into the cell.  The enzyme invertase is located in the outer layers of the cell wall however some leaks into the beer but fortunately is quickly deactivated by heat. The glucose located inside the cell is phosphorylated using ATP by the enzyme hexokinase to yield glucose 6-phosphate while fructose is phosphorylated to yield fructose 6-phosphate because subsequent enzymes recognize only phosphorylated compounds. The metabolism of glucose proceeds by the glycolytic pathway that contains 10 enzymes that oxidize the six-carbon sugar to two molecules of pyruvate and through this process two molecules of ATP and two of NADH are gained (Lewis & Young, 1995).

The job of a brewer is to combine all of the ingredients discussed and pursue fermentation, which lasts 10 days to several months depending of the beer style. During this time the yeast will reproduce and disperse throughout the fermenting beer while converting sugars to carbon dioxide, alcohols, a variety of flavors. The yeast will have run through its supply of sugar and will began to settle at the bottom of tank, or other fermentation vessel, after the initial 5 to 14 days. Most brewers will transfer the clear beer top layer to a different tank and once the fermentation process is over the beer is packaged in the designated bottle, can, or keg. Some breweries choose to filter the beer for preservation purposes as well as some economic reasons but some breweries prefer to not do so because it may take some of its special character away along with the things being filtered out.

The fermentation temperature and quality of the yeast will determine how long the beer should be aged or if it should be done at all. Beer made with Ale yeast and with a fermentation temperature above 65 degrees Fahrenheit will be ready for bottling in about 2 weeks more or less. If the beer is made with very high quality lager yeast and a fermentation temperature below 45 degrees Fahrenheit, then aging can be advantages (Papazian, 2003).

One of the most important things to avoid during the brewing process is the growth of unwanted organisms. The science of microbiology involves the study of organisms less than 1 mm in size. Prokaryotes, which have no nucleus, as well as eukaryotes, which do have a nucleus, are both important in the brewing process but for very different reasons. Prokaryotes are the main concern when beer spoilage occurs. On the other hand eukaryotes are divided into lower and higher eukaryotes and the lower group includes the brewing yeast, wild yeast, and other fungi or molds. Unfortunately microorganisms are found anywhere if the right nutrients and other conditions are present even in air. For example, acid-tolerant bacteria are capable of surviving in beer because they can grow in the absence of oxygen and given the right nutrients will grow perfectly in an acidic anaerobic environment. It is very important to make sure that the brewer does not provide the right environment for these organisms to grow because they may be detrimental to the beer and the person who drinks it. The brewer’s job is to monitor their equipment and product for the appearance of any unwelcome microbes. This can be very difficult because microbes survive best in places where water is abundant and water, malt and cereals, sugars and hops all provide a good environment for microbes to flourish.

Microbes found in brewing are usually gram positive, gram negative, or simply wild yeast. The most important members of the gram-positive group are lactic acid bacteria, Leuconostoc, streptococcus, micrococcus, and Bacillus. The ones that have become the greatest concern to brewers are the lactic acid bacteria specifically Lactobacillus and Pediococcus because they are found most often and can spoil the beer by making it more sour, turbid and producing diacetyl which gives an unwanted smell and flavor.  Pediococcus is encountered more often than Lactobacillus but fortunately they can both be isolated using the same type of media.

The gram-negative bacteria include Enterobacteriaceae, acetic acid bacteria, Zymomonas, Pectinatus, and Megasphaera. Enterobacteriaceae for example, which is a bacteria encountered if poor cleaning methods are used, can spoil the beer by affecting the wort and growing quickly producing dimethyl sulfide and diacetyl. If they affect the beer during the beginning stages of fermentation they can produce an unwanted taste in the beer or even decrease the growth of the yeast (Lewis & Young, 1995).

Like stated earlier, wild yeasts can give an undesirable taste and aroma to the beer. Any yeast that is not considered a brewing strain is said to be a wild yeast. Unfortunately wild yeasts can become a huge problem specifically cause they are extremely hard to detect and are not as easily removed. They can really change the taste of the beer if they affect the beer in early stages as well as make it cloudier in appearance.

During the brewing process it is important to take certain readings and make specific observation such as temperature, specific gravity, pH, cell count, etc. A hydrometer is an instrument used to measure the density of a liquid relative to the density of water. This is also known as the specific gravity. Because the density of water was determined to be 1.000, it is known that the density of the beer will be higher because of all of the components added to the water. In result the specific gravity will also rise to about 1.035 to 1.042. Once the yeast begins to ferment the dissolved sugars into alcohol and carbon dioxide, the density will begin to decrease because of the reduction in sugar content and also because alcohol is less dense than water. A digital gravity meter can also be used to measure the specific gravity of samples taken from tanks in the laboratory setting.  

The common media used to determine what organisms are growing in the beer are Mac Conkey agar used to detect coliforms, Plate count agar/PCA used to detect all forms of bacteria, Walerstein nutrient medium/WLN used to detect all forms of bacteria, Schwarz differential medium used to detect only wild yeast, Lysine medium used to detect only wild yeast, and Raka Ray medium which is an anaerobic medium (LinkedIn, 2014). Other media used include LWYM (Lin's Wild Yeast Medium) used to detect saccharomyces wild yeast, LCSM (Lin's Cupric Sulfate Medium) used to detect non-saccharomyces wild yeast, HLP (Hsu's Lactobacillus/Pediococcus Medium) used to detect the growth of Lactobacillus and Pediococcus and WLD media used to detect all bacteria and wild yeast while impeding the growth of brewer’s yeast. To plate the beer samples on each of the media the membrane filtration method or the spread plate method can be used and then they are either incubated aerobically or anaerobically. Finding Saccharomyces species is very important because 3 of 11 killer yeasts are displayed within the Saccharomyces genus. These killer yeasts produce toxins that are lethal to other yeast strains and they are immune to toxins themselves (Hammond & Eckersley, 1984).

Some of the tests and measurements commonly used in the laboratory setting for quality assurance are the international bitterness unit (IBU) test, pH test, gravity test measured in degrees Plato (density of beer wort in terms of percentage of extract by weight), cell counts/viability, and standard reference method (SRM) test. The IBU test simply measures the bitterness of the beer, which is usually caused by the hops added. The pH of the beer usually starts to increase when the beer is almost ready because of this it is important to measure the pH everyday until it is constant or begins to increase. The original gravity is the gravity of the sample before yeast is added and the final gravity is that which is measured when the beer has finished fermenting.  The original gravity of wort is important because it has been shown that as it increases the ethanol concentration of the beer coming out increases as well (Dragone, Mussatto, & Almeida e Silva, 2007). This can produce unbalanced flavor in the beer, which can be undesirable. The gravity will decrease as the beer finishes off because the yeast will have fermented most if not all of the fermentable sugar to alcohol, which is less dense than water. The SRM test is used specify beer color by measuring the attenuation of light at a particular wavelength (430 nm) when passing through 1 cm of the beer and is done by using a spectrophotometer.  The purpose of taking cell counts is to determine the concentration of cells per mL of beer and the viability simply shows how effective or viable the yeast in that sample is. The cell count should decrease towards the end of the brewing process and the viability should always be close to or at exactly 100% although it might be slightly lower when the yeast is first pitched in. If the viability is low than there is definitely something wrong and this should be checked immediately. Checking for all of these measurements is extremely important so that the beer is at its best quality possible and no money is lost by having to dispose of an entire tank of beer simply because quality control was not adequate.

All in all it is extremely important to follow all quality assurance protocol so that large quantities of beer are not lost by contamination or any other reasons. Microbes are everywhere and avoiding their contact with the beer is vital. Knowing ways to detect or prevent contamination is one of the most significant attributes of any brewery or homebrewer.  Understanding the importance of all the ingredients included in the brewing process from the malt to the hops and even the type of yeast and water used is very pertinent in beer making because only through this comprehension will you understand why they are added at a certain stage of the process and not others. Each and every ingredient provides some character to the beer and all of them together in the right amounts will make the perfect beer. Whether someone is brewing at home or for a large Brewery this paper can help understand the basics of the beer making process

 

Bibliography

 

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