Brewing Process(book excerpts)
Beer is part of the history of civilization. There is evidence that people have been drinking beer since 3500 B.C. Beer is one of the most widespread and largely consumed alcoholic drinks in the world. It is a complex alcoholic beverage, containing numerous flavor-active compounds over a wide range of concentrations. Brewing is the process of producing of beer. The object of the entire process is to convert grain starches to sugar, extract the sugar with water, and then ferment it with yeast to produce the alcoholic, lightly carbonated beverage. Beer is more than just water, hops, malt, yeast, and possibly adjuncts. In the process in making beer, it involves malting, milling, mashing, extract separation, hop addition and boiling, removal of hops and precipitates, cooling and aeration, fermentation, conditioning, carbonation, and packaging.
The first step in the production of beer is malting. Malt contains a range of carbohydrates, composed of insoluble cellulose and soluble hemicellulose, dextrin, starch, and sugars. Starch, which accounts for about 50 to 60 percent of the weight of malt. To harvest that starch and convert it into sugars, the barley undergoes a process known as malting. The barley is soaked in water and the “germ” part of the seed begins to grow into the acrospire, i.e., germinate. This process activates, and develops diastatic enzymes inside the seed and also starts the process of unlocking starches from the endosperm, i.e., converting its stored starch into sugars. Plain, pale malt accounts for up to 100 percent of a brewer’s grain bill depending on beer style.
The second step in the brewing process is milling. In order to use the malt in the brewing process, the brewer has to break open the husks and expose the starch in the grain. Doing so also allows the enzymes that were formed during germination to be released once the crushed malt is added to water. The husks should be crushed as little as possible in order to prevent the undesirable tannins, bitter compounds, and coloring substances, which could have an adverse effect on the taste of the beer. The malt is milled according to the wort separation process (i.e., sparging). In some cases, the malt is barely crushed. In other cases, the malt is essentially converted into flour.
Hops is used in brewing to impart both bitterness and floral character. The flavor-active components of hops are resins (e.g., alpha-beta acids) and essential oils. The bitter character of hops is due to alpha acids, also known as humulones. The alpha acid content is a characteristic of particular hop varieties and varies between 2 and 15 percent of the weight of the hop cone. During the copper boil the alpha acids undergo isomerization to form the cis and trans forms of the humulones. It is these iso-alpha acids that impart the bitter character to beer.
Yeast management is key to the efficiency of brewery fermentations and to the quality of the final beer. Important steps in maintaining the vitality and viability of the culture yeast are the proper pitching and cropping of the yeast, the propagation of the yeast from laboratory to full-scale pitching, its storage for reuse, and the techniques for acid washing the yeast to reduce infection. Yeast is pitched into the wort, either directly into the cooled wort in the fermentation vessel, or in-line en route from the heat exchanger to the fermenter. Typically, 5 to 20 million yeast cells are pitched per milliliter of wort.
In brewing, adjuncts are unmalted grains such as corn, rice, rye, oats, barley, and wheat or grain products used in brewing beer which supplement the main mash ingredient (e.g., malted barley). This is often done with the intention of cutting costs, but sometimes also to create an additional feature, such as better foam retention, flavors or nutritional value or additives. Adjuncts such as rice or maize are not pre-germinated and do not contribute with supply of enzymes. Furthermore, their starch has a higher gelatinization temperature than malt starch.
The mineral composition of water used for mashing is very important the brewing process. In order to maintain the highest product quality, brewing of different beer styles requires water (liquor) with particular ionic composition. Thus, availability of appropriate local water supplies accounts for the rise to prominence of the more famous centers of brewing excellence. For example, the reputations of towns and cities such as Pilsen, Dublin, Burton-upon-Trent, Dortmund, and Munich are largely based on the qualities of the local water.
Once the malt is milled, it undergoes the process referred to mashing. The purpose of mashing is to obtain a high yield of extract (sweet wort) from the malt grist. The grist, broken pieces of grain and husks, and warm water and possible adjuncts are mixed and added to the mash tun or mash mixer, forming a porridge-like mixture called the “mash.” Water is combined with the grist in one of two ways, infusion or decoction. In infusion mashing, the grains are heated up in one vessel (the mash tun); in decoction mashing, a portion of the mash is transferred from the mash conversion vessel (often called mash mixer) and boiled in a separate vessel (called the mash kettle), where it undergoes gelatinization, then returned to the original mash. During mashing, enzymes developed during the germination (malting) process convert the available starches to sugars.
Wort separation, often referred to as lautering, is the process of separating sweet wort from the grain bed. Sparging is the rinsing of the mash grain bed to extract as much of the sugars from the grain as possible without extracting tannins in the process. There are a variety of approaches to accomplish this task. In some instances, the lautering and sparging can occur in the same vessel—commonly referred to as the “mash tun.” In other instances, the entire mash (grist and sugar-water) is pumped from the mash conversion vessel to a different vessel known as a lauter tun. Another method is to use a combined mash tun/lauter tun, typically used by craft brewers. In these vessels the wort is slowly drained from the grain bed while being gently rinsed repeatedly with warm water (sparing).
After the lautering and sparging, the sweet wort is boiled together with hops, the flowers (so-called cones) of the female hop plant which provide flavor to beer. Depending on when the hops are added to the boil, they can contribute the characteristic bitter flavor or provide the characteristic aroma. Bitter hops contain high concentrations of alpha acids and are often added at the beginning of the boil. Aroma hops have a high hop oil content are typically only added towards the end of the boil. Hops give us the crisp, citrusy flavor found in pale ales, the bitter taste of a stout, and the characteristic aroma of India Pale Ales (IPAs). The boiling serves several purposes: sterilization, deactivation of enzymes, protein precipitation, color formation, wort concentration, removal of unwanted volatile components and, very important, the conversion (isomerization) of the main constituents of the hops, the alpha-acids, into the iso-alpha-acids, the main bittering compounds found in beer.
Hop Trub Rmoval
The next step is to remove that the coagulated material (i.e., trub) formed during the boil. Trub, from the German word meaning “sediment,” is a collective term covering sediments formed in the brewing process during wort boiling—also called hot break. Hot trub can impede fermentation and produce undesirable qualities in the finished beer. There are several methods for removal, depending on the equipment available and also whether whole hops or hop products that are used: hop back/hop strainer if using whole hops, centrifuge, sedimentation/flocculation, filtration, and whirlpool.
After the boiling, the wort is cooled by a heat exchanger and solid materials, precipitated proteins, spent grain, and spent hops, are removed and the clear liquid (hopped wort) is ready for fermentation. Cooling the wort rapidly once the boil is complete can have three main advantages: reduced dimethyl sulfide (DMS) formation, increased cold break, and reduced risk of infection from beer spoilage organisms.
Cold Trub Removal
The very fine flaked cold trub appears after cooling. It consists of around protein, combined with polyphenols, and carbohydrates. Opinions are divided regarding the necessity of cold trub separation. The presence of cold trub can, under certain circumstances, accelerate fermentation because of the presence of long-chain unsaturated fatty acids. In other cases, the yeast will contain a higher level of impurities and the filterability of beer brewed in this manner may be poor. A fairly good separation of the cold trub can be obtained in the starting vessel by sedimentation after pitching.
There are two main classifications of fermentations, ale and lager, but a wide variety of different fermentation systems. In brief, ale uses a Saccharomyces cerevisiae, top-cropping yeast at a temperature of 14 to 17 degrees C (57–63°F). Lager ferments at a lower temperature, typically 8 to 13 degrees C (46–55°F), and uses a bottom-cropping Saccharomyces uvarum yeast. During the main fermentation phase, yeast converts the fermentable carbohydrates in the wort into ethanol and carbon dioxide. During fermentation numerous other flavor-active volatile components, such as esters, aldehydes, and higher alcohols, are being formed as by-products, which have an important contribution to the flavor of the final beer.
When fermentation is complete the green beer must be rendered into a form suitable for consumption. Many options are possible depending on the type of beer. Beers subject to a secondary fermentation are removed from the primary fermentation vessel after the bulk of the yeast has been removed and transferred to a vessel where it undergoes a long lagering period or transferred to either a cask or bottle. These days such types of beers are comparatively rare. Most beer is subject to post-fermentation cold maturation to produce a packaged product, which is stable, both from microbiological, physical and flavor standpoints. Green beer contains too many undesirable flavor components such as acetaldehyde, diacetyl, and dimethyl sulfide, also formed during the main fermentation.
Once the beer has undergone the full maturation process, it can be filtered to remove any of the solids and haze that remains. The solids and haze can be made of a number of different things, but are primarily the result of excess proteins and tannins in the beer that weren’t removed during the boiling, fermentation, or conditioning. These compounds bind together until they become insoluble in the beer and form either haze or solids that slowly settle. Removing these from the beer improves the clarity and increases the shelf life of the beer.
Once the beer has been filtered, it undergoes carbonation, but not required for beers subject to secondary fermentation. Carbonation strongly influences a beer’s mouthfeel, flavor, aroma, and appearance. Beer without carbonation is said to be “flat,” and this is an apt description, as the beer is likely to be dull and lifeless. Traditionally, carbonation was achieved in the brewery by transferring the beer to a bright beer tank with some residual fermentable sugar, and allowing a secondary fermentation to finish the beer. .
Finally, the beer must not contain any beer spoilage organisms before bottling. One method to achieve this, especially for beer that is expected to have a long shelf life, is pasteurization, where the beer is heated to 60 degrees C (140°F) to destroy all biological contaminants. Alternatively, the beer can be sterile filtered. Bacterial infections in a brewery are possible, and if they occur, they can impart undesirable flavors (such as sour, rotten, and bitter flavors). Removing the bacteria and yeast stabilizes the flavor and results in a product that doesn’t change its flavor much, if kept cold.
Beer is about 95 percent water in composition; however, the amount of water used to produce a container of beer is far greater than the amount of water contained in the beer that is actually packaged and shipped out. Inside the average craft brewery, it takes seven liters of water to produce one liter of beer. At less efficient breweries, the ratio can go as high as 10 to one. A large amount of water is used for cleaning operations. In addition to water usage, there is the issue of wastewater discharge that the brewery has to manage.