Below is a description of the brewing process, including its steps and chemical reactions that take place in order to produce a batch of beer. All steps from creating the mash through carbonation are detailed below.
Mashing is the steeping of crushed grains in a specific amount of water, for a specific amount of time, at a specific temperature. On the biochemical level, the heat of the water activates enzymes to convert the starches in the grains to fermentable sugars that the yeast will later consume and process into carbon dioxide and alcohol. When the starch-to-sugar conversion is complete, the liquid is separated from the grains, a process known as lautering, and collected in the boil kettle.
Mashing can take anywhere from 60 minutes to several hours. A variety of mashing techniques and temperature rests (letting the wort sit for a time in a particular temperature range) are often employed depending on the beer style and the type of grain used. There are two main mashing techniques. In a “Step Mash,” the mash is held at certain temperatures, called steps, or rests, allowing the activation of different enzymes which results in a variety of modified (converted) sugars, proteins, and other grain components. In an “Infusion Mash,” crushed grains are added to water heated at one specific temperature within the range of a saccharification rest, and the target mash temperature is held for the entire period of the mash.
Lautering is the method of separating the sweet wort (water dissolved sugars extracted from the grain during the mash) from the mash. A lauter tun consists of a large vessel to hold the mash and a false bottom or manifold to allow the wort to drain out while leaving the grain behind. Lautering can be conducted in several ways, but is usually consists of three steps: mash-out, recirculation, and sparging.
The timing of lautering varies based on how slowly or quickly the mash is rinsed. This step is complete when the wort reaches the desired volume and pH.
1. Mash-out is the term for raising the temperature of the mash to 170F prior to lautering. This step stops all of the enzyme action (preserving the fermentable sugar profile) and makes the grain and wort more fluid.
2. Recirculation, also known as the vorlauf step, occurs after the grain bed has settled and is ready to be lautered. The first few quarts of wort are drawn out through the drain of the lauter tun and poured back in on top of the grain. This helps settle the grain bed to ensure proper mash filtration and clarity.
3. Sparging is the process of rinsing the grain bed that has settled at the bottom of the lauter tun in order to extract the remaining sugars. The temperature of the sparge water is carefully controlled so as not to also extract tannins from grain husks.
During lautering, the wort is separated from the grain. It is then brought to a boil and held there, typically for 60-90 minutes. There are multiple reasons to boil the wort, but it’s not done for all beer styles. Boiling does the following:
- Stops enzymatic activity (no more conversion of starches to sugars), known as ‘denaturing’ enzymes
- Blows off undesired volatile compounds including hop oils, sulfur compounds, and dimethyl sulfide (DMS)
- Encourages ‘hot break’, which is a coagulation of proteins and tannins that improves the beer's’ clarity and decreases astringency
- Concentrates wort through evaporation
- Converts hop alpha acids into isomerized hop alpha acids that provide bitterness to the beer
- Kills off any microbes that may be in the wort, thus sterilizing it
Whirlpool happens after the boil and serves to collect hop particulates and coagulated protein from the hot break (a term for aggressive foaming that happens as the wort begins to boil). This often happens in a dedicated vessel, or can be done in the boil kettle. The beer is spun in a circular fashion, allowing particles (called ‘trub’) to collect together at the bottom center of the vessel. The wort is then siphoned away, leaving the trub behind.
The wort is chilled to prepare it for fermentation. Methods of chilling include immersion chillers, which are set inside the wort, and heat exchangers that pass wort and cold water through a parallel set of coils, thereby cooling the hot wort indirectly. The wort is commonly chilled down to yeast-pitching temperature, which varies on the yeast strain being used and the brewer’s intentions.
Fermentation begins when yeast or microorganisms are introduced to the sweet, cooled wort. Fermentation can last for several days, weeks, or months depending on the brewer’s intentions and the style of beer. Ales ferment faster and warmer than lagers, which require a slow conditioning period. Ales can ferment and mature as quickly as three weeks. Lagers traditionally require more than 40-60 days’ time.
Fermentation most commonly occurs in steel tanks or wood barrels. Yeast needs oxygen to begin fermentation so oxygen is often added at the same time the yeast is pitched. Primary fermentation is when the yeast is the most vigorous and active. As yeast consumes the fermentable malt sugars, it begins to settle to the bottom of the tank (a process called ‘flocculation.’) Secondary fermentation is when the initial yeast cake (dormant yeast at the bottom of the fermenter) has been removed, and the beer continues to ferment at a slower pace. Beer also begins to clarify during this time.
Conditioning is the term for the end period of fermentation when the yeast has stopped fermenting the wort and has finished settling out to the bottom of the fermentor. This is also the period when yeast byproducts such as diacetyl and acetaldehyde are lessened or completely removed. Note that these by-products are acceptable at lower levels in some beer styles.
Carbonation is a key aspect of beer. It lends body or weight on the tongue and stimulates the trigeminal nerves, which sense temperature, texture, and pain in the face. Carbonation can be detected as an aroma (carbonic acid). It also affects appearance and is what creates the collar of foam, or 'head,' common to most beer styles.
Carbonation is introduced into beer in a variety of ways:
- Natural Carbonation: As yeast eats sugars during fermentation, it produces a variety of byproducts, including alcohol and CO2. This carbonation can be captured and used to carbonate the finished beer.
- Force Carbonation: One method of force carbonation is via a device called a carbonation stone. This device injects CO2 from a separate gas tank into beer that resides in a conditioning or serving vessel. It allows CO2 to dissolve into the beer.
- Bottle Conditioning: Addition of yeast at packaging time. This yeast, under the right conditions, will ferment residual sugars still left in the beer and then produce CO2 that dissolves directly into the beer in the bottle. Successful bottle conditioning requires residual sugars and yeast to still be present in the beer. It is a common technique used by smaller brewers and homebrewers.
The 4 main ingredients in beer are: Malted Barley (Malt), Hops, Water, and Yeast. There are also other forms of fermentable sugars, along with microorganisms that are also involved in certain beer styles. Below is a description of the main ingredients.
1. MALTED BARLEY (MALT)
Typical Flavor descriptors: Bread flour, grainy, biscuit, bready, toast, caramel, pruny, roast, chocolate, coffee, smoky, acrid
Malt is detected in the aroma, flavor, and appearance of a beer. It has been called the soul of beer. It is the main fermentable product providing the sugars that yeast use to create alcohol and carbonation. It is most often barley that has been malted by putting it through a series of moisture and temperature steps. Malt adds fermentable and nonfermentable sugars and proteins that influence beer’s aroma, alcohol, astringency, body, color, flavor, and head retention.
Malt is converted barley or other grains that have been steeped, germinated, heated, kilned (or roasted in a drum), cooled and dried, and then rested. Fresh barley has a moisture content commonly around 13%. This is raised, often to more than 40%, until the barley begins to germinate. During the malting process it is dried to less than 4% moisture.
A wide variety of barley and other malts are used to make beer, including: pale malts (pilsner, pale two-row), higher temperature kilned malts (Munich, Vienna), roasted/specialty malt (Chocolate, black), and unmalted barley. Wheat malt is commonly used as well.
Other Ingredients & Fermentables
Adjuncts include anything that is not malted, but is a source of fermentable sugars, flavor, color or other characteristics. Common adjuncts include: Candy sugar, honey, molasses, refined sugar, and maple syrup. Unmalted starchy adjuncts include: Oats, rye, wheat, corn/maize, and rice. Many adjunct grains can be malted to create unique flavors compared to their unmalted counterparts. Other ingredients include fruit, herbs, roasted (unmalted) barley or wheat, spices, and wood.
Aroma and flavor descriptors: Citrus, Floral, Fruity, Green, Herbal, Onion/Garlic, Pine, Resinous, Spicy, Spruce, Sweaty, Tropical, Woody
Bitterness ranges: Restrained, moderate, aggressive, harsh
Hops deliver both resins and essential oils that influence beer’s aroma, flavor, bitterness, head retention, astringency, and perceived bitterness. They also increase beer’s stability and shelf life. Brewers today use well over 100 different varieties of hops worldwide, with hops grown in the US contributing an estimated 30 percent of the global supply, and Washington and Oregon 70% of the US’s supply. Though there are many varieties of hop plants, the hops used in beer generally fall into three categories: bittering, aroma and dual-purpose. Bittering hops contain more alpha acids and are used primarily to contribute bitterness, while aroma hops are used primarily to add flavor and aroma to beer. Dual-purpose hops can have higher alpha acid content, but also are used to contribute aroma compounds.
Hop resins lend bitterness via alpha acids to balance the sweetness of malt sugars. When Alpha acids are isomerized through boiling, ranges of bitterness can lend anywhere from 2 IBUs (International Bittering Units) to more than 100 IBUs depending on the beer style and brewer’s intentions. Alpha acid content of most hops ranges from 2-20 percent by weight. Aroma hops contain higher level of essential oils, which influence aroma and flavor. These oils volatilize when exposed to heat. so aroma and flavor hops are added at the end of the boil or during/after fermentation (a technique referred to as “dry hopping”).
Beer is mainly water, which makes water quite an important ingredient. It provides minerals and ions that add various qualities to the beer. Some brewers make their beer without altering the chemistry of their water sources; however, many do modify the water to make it most suitable to deliver the beer characteristics they hope to highlight. Common minerals include carbonate, calcium, magnesium, and sulfate. Common taste descriptors include chalk, flint, and sulfur. water hardness or softness, pH, residual alkalinity, and mineral content all come into play when brewing beer.
- Hardness is the concentration of minerals in water. Water high in calcium/magnesium and bicarbonate/sulfate is said to be ‘hard.’ Hard water is used in German-style Dunkels, German-style Marzen/Oktoberfest beers, Vienna-style Lagers, Irish-style Dry Stouts, Scottish-style Ales, and English-style Pale Ales/ESBs. On the other end of the spectrum, water low in these ions is said to be ‘soft’. Soft water is used in styles like Bohemian-style Pilsners. The presence of calcium sulfate (gypsum) enhances bitterness, but also can induce dryness and lend a low sulfuric character. This effect has been called the ‘Burton Snatch’ originating from beers made in Britain in the Burton-On-Trent area.
- pH measures the concentration of ions in a liquid. The pH scale runs from 0 (acidic) to 14 (alkaline), with 7 as the neutral midpoint. Acidic (0-6) has higher hydrogen concentration, Alkaline (8-14) has higher hydroxide concentration. Darker kilned and roasted malts decrease the pH. Too alkaline a mash lessens the chance for proper malt color extraction. Ideal pH ensures:
- Ideal enzyme conditions for proper saccharification (conversion of malt starch into fermentable sugars)
- No leaching of harsh tannins/polyphenols from malt husk
- Proper ‘hot break’, which aids in coagulation of proteins during the mash boil
- Alkalinity determines the buffering capacity of water (the degree to which water will reduce the acidity of the beer). Calcium and magnesium affect hardness. Carbonates and bicarbonates affect alkalinity. Together they affect the mash pH. To lower alkalinity, brewers:
- Add dark malts to lessen pH to a more acidic environment
- Use brewing salts
- Add acidic compounds like lactic acid or acidulated malt
- Conduct a sour mash (a particular mixture of grain and water that encourages the development of bacteria that produces lactic acid, which is present in the husk of barley.)
- Ions in brewing water primarily affect pH and may add or accentuate certain flavors. Calcium is the most important ion for brewing, and lowers the mash pH. Magnesium also lowers the mash pH. Bicarbonate is the most important ion for alkalinity. It raises the pH and reacts with calcium to reduce hardness during boil. Chloride increases mouthfeel, and accentuates bitterness and dryness.
Yeast and other microorganisms contribute over 40% of the flavor compounds in beer. They eat sugars from malted barley and other fermentables, producing carbonation, alcohol and aromatic compounds. The flavor imparted by yeast differs based on yeast strain, temperature, time exposed to the beer, oxygen and other variables. There are two primary types of yeast, Lager and Ale, as well as wild yeasts:
- Lager: Saccharomyces pastorianus (formally known as Saccharomyces carlsbergensis), often lend sulfuric compounds. It is commonly referred to as bottom-fermenting, most often fermenting at cooler temperatures (45-55F).
- Ale: Saccharomyces cerevisiae, generally produces more flavor compounds (esters and phenols). It is commonly refereed to as top-fermenting, and most often ferments at warmer temperatures (60-70F).
- Brettanomyces: Considered a “wild” yeast, it lends flavors like barnyard, tropical fruit and more.
There are also three main types of other microorganisms (bacteria) that ferment beer:
- Acetobacter: Bacteria that makes acetic acid, which gives vinegar its tart quality.
- Lactobacillus: Bacteria that produces lactic acid, which gives yogurt and sourdough bread their sour qualities.
- Pediococcus: Bacteria that produces lactic acid. Over time, this can create diacetyl (an off-flavor in beer that is often described as buttered popcorn.)