Traditionally undertaken by maltsters generally operating in a dedicated malt house, malting is a process that converts raw grain into malt. For brewing the grain is primarily barley, but other commonly used types include wheat, rye, and on occasion sorghum. Modern practices germinate and subsequently produce a much larger grain mass than traditional floor maltings did previously. An in-depth examination of the process is to follow.
A farmer delivers the raw grain at the malt house, where it is cleaned, dried, and subjected to a variety of tests checking its malting suitability and to ensure no infected or dead grain embarks on the remainder of the malting journey. Some of these initial checks include measuring the grain moisture content, nitrogen content, water sensitivity, germinative capacity, absence of fungal growth, and amount of foreign material present.
Initial grain drying is necessary for raw grain that arrives with too high a moisture content to allow for safe storage without damaging its germinative capacity. Not too-hot heated air is circulated through the grain just long enough to remove the moisture without killing the barley embryo.
Cleaning the barley is done to remove dust, chaff, straw, stones, or metals. A varitey of implements are employed in order to do so. Rotating and shaking sieves weed out undesireable foreign matter larger-than or smaller-than barley grains. Magnets are used to remove any metals, and aspiration systems remove dust and chaff. After cleaning is complete the grain mass is weighed and the difference from received weight recorded before it is transferred to storage.
The barley must be properly stored in order to maintain its germination viability. It is often stored in temperature monitored and controlled silos with a system for rotating grain from one to another in order to diminish hot spots within the grain that may be indicative of insect growth.
Steeping defines the beginning of the active malting process. The grain is covered in steeping water to approximately quadruple its moisture content by alternately submerging and subsequently draining the grain for multiple cycles. During the submersion process air is periodically bubbled through the mixture to stimulate barley growth, equilibrate hydrostatic pressure in the steeping vessel, and loosen remaining dirt. During the air rest phase fans remove excess CO2 produced by grain respiration while providing fresh oxygen at increasing flow rates at particular temperatures.
Grain growth is the goal of germination. This stage of the malting process allows for the development of malt enzymes which modify the endosperm structure of the barley grain by breaking down its protein matrix and cell walls which allows for optimal starch utilization during brewing.
Kilning occurs in three stages designed to stop the germination process, reduce moisture content, limit the DMS potential of the malt, and provide a remarkable range of colors and flavors in the finished product. During the initial drying phase cool air temperatures dry the grain without causing enzymes to denature. During the second phase of kilning temperatures are raised to further dry the grain to a target moisture content of approximately 5%. In the final curing phase the air temperature is raised above 80° C to break down S-Methylmethionine (SMM) to Dimethyl sulfide (DMS - a potential source of sweetcorn-like off-flavor in finished beer product) in order to reduce the DMS potential of the malt. It is during this phase that color and associated roast flavors are produced in the malt through the Maillard reaction, a chemical reaction between amino acids and reducing sugars.
Hops are the flowers of the hop plant Humulus lupulus, and are used in brewing partially for their preservative qualities and for their antibacterial effect that favors the activity of yeast over other undesirable microorganisms which may present themselves during the brew process. Primarily hops are used because their bitterness balances malt sweetness and they can impart a vast range of flavors and aromas.
Hop plants are vigorous climbers that are trained to scale trellises designed to maximize sunlight utilization. Commercial hop cultivation is concentrated in wet temperate climates with soil composition similar to that required by potatoes. They are planted in row a couple meters apart and each spring the roots send forth bines that snake around strings leading to an overhead trellis. The hop cones grow high up on these bines.
Hop harvesting is done at the end of summer. Bines are pulled down and nowadays the hop cones are mechanically separated from them before being transported to a two-story hop house for drying. The hops are spread and raked evenly across the burlap covered floor of the upper story. The lower story has a heating unit used for drying the hops. Once dry they are moved to a press and compressed into bales.
Hops are composed of various proteins, a hearty amount of cellulose, and water, but beyond that, their true character comes courtesy of different oils. Perhaps the most important of which is an oleoresin, lupulin. Lupulin contains humulones and lupulones, alpha and beta acids, which are responsible for bitterness and possess antibiotic properties.
Alpha acids are thermally isomerized into isohumulones during the boil phase of brewing, providing bitterness. Beta acids are sensitive to oxidative decomposition over time and are thus selected against, low-beta acid content is preferable. Terpene hydrocarbons such as myrcene and humulene are responsible for the pungent aroma of hops. Varying degrees of these alpha acids and essential oils provide us with the rich diversity of flavors and aromas encountered in the hundreds of hop varieties cultivated.
In order to brew a good beer, it's necessary to create a good recipe. A beer recipe is comprised of among other factors, a grain bill, water minerality profile, water volumes, hop bill, and the yeast type to be used.
The grain bill of a beer recipe defines the varieties and quantities of malted grains to be used.
Once a recipe has been established, the grains presented in the grain bill must be milled. Milling of the malted barley is performed to better allow the mashing liquor to access the center of the grain. With most of the endosperm broken up and exposure to greater surface area, conversion rates of starch to sugar will be higher during the mashing stage. It is vitally important that the husks remain intact in order to provide a functional filter bed during the lautering stage. Milling the malt too finely will result in too sludgy a mash, and ultimately haziness in the final product. Not too fine, not too coarse, but just the proper degree of malt structure will provide optimal starch to sugar conversion rates. Once milled the malt is referred to as grist.
The minerality and pH of a beer's mash water can be modified to mimic the water profile desired for a given style of beer by the addition of various salts. Different stages of the brewing process perform optimally at different pH ranges. In order to optimize the enzymatic action of starch to sugar conversion during the mash phase a pH within the range of 5.1-5.5 should be maintained. A proper pH range for wort during latter stages of brewing help the coagulation of proteins, and an optimal pH range during fermentation will promote yeast health while being an unkind environment for bacteria. All in all, water is an underappreciated facet of brewing that bears much influence on the overall quality of the finished product.
During the mash phase of the brew process, grist is immersed in water in the mash tun in order to convert the starches present in the endosperm of the malt into smaller sugars. Milled barley sugars are long-chained unfermentables. The extraction of fermentable sugars from the grist happens by dissolving starches and breaking up the starch chains enzymatically. This process results in a sugar water solution called wort. This sugar rich solution defines the malt backbone of the beer and will ultimately provide yeast an environment in which they may thrive.
Once the mash phase is complete, the grain and wort slurry is transferred to the lauter tun wherein the goal is simply to extract as much fermentable sugar as possible from the grist. The grist acts as a filter through which the existing wort passes on its way to the boil kettle, clarifying the wort in the process. More water is sporadically introduced on top of the grist in a process called sparging, in order to continue the sugar extraction process and to achieve a desired wort volume for the boil.
Once the desired wort volume has been collected, it is heated to a boil. Once a boiling temperature has been achieved it is common to introduce a bittering charge of hops. Hops: Hops are added at various stages during the boil phase according to the quantity and varieties defined by the hop bill. Early stage hop additions largely impart bitterness due to the time dependence of alpha acid isomerization. Hop charges introduced at latter stages of the boil will largely contribute to the aroma and flavor profile of the end product. Duration: The length of boil time will affect caramelization of the wort and alpha acid extraction magnitude of the added hops. The standard boil time for most beer styles is 60 minutes. The boil is naturally responsible for sterilization and ensures that contamination won't occur during fermentation assuming necessary cleaning protocols have been adhered to for the receiving vessel.
Once the boil is complete, the now hopped wort is sent onwards to a vessel known as the whirlpool or 'settling-tank' where the wort is generally introduced at an angle to promote the whirlpool motion of the liquid and the accompanying centripetal force will force denser solids in the wort to settle into a shallow oblate spheroid toward the center and bottom of the vessel. The solids known as 'trub' are simply vegetable matter from the added hops and coagulated proteins from the grain.
After enough time in the whirlpool to allow for much of the trub to precipitate, the wort must be chilled to a temperature range suitable for fermentation. The wort is passed through a heat exchanger which will quickly drop the temperature of the wort from near-boiling to between 9° C – 26° C.
As the chilled wort passes through the heat exchanger it is aerated with either sterile air or pure oxygen on its way to a cylindroconical vessel known as a fermenter. Yeast is introduced at this point, generally inline. This defines the end of the brewing process proper, and from here on the real stars of the show do what they do best, consume sugars and produce CO2 gas, acids, and importantly alcohol.
Brewer's yeast generally falls into two broad categories, ale yeast (Saccharomyces cerevisiae) and lager yeast ( Saccharomyces carlbergensis/Saccharomyces uvarum), with a third much less common complex hybrid of Saccharomyces cerevisiae and Saccharomyces kudriavzevii. Ale and lager yeasts are available in dozens of strains that produce the wondrous range of flavors and scents we experience in finished beer. The mechanics of the process however doesn't much change.
Yeast can utilize many nutrients and the composition of its environment influences the types of metabolic processes that the yeast engages in. In the presence of high sugar concentrations encountered in wort fermentation, yeast produce carbon dioxide and alcohol as byproducts. The fermentation process is intimately linked to the process of yeast growth. As the yeast consume the sugar rich wort, their cell size and quantity grow, spurring increased fermentation rates until a critical point is reached and fermentation slows.
The modern closed fermentation cylindroconical fermenter has a conical bottom and cylindrical body, fine grained temperature control, and effective gas exchange features. During active fermentation yeast are rather evenly suspended in solution and eventually colloids flocculate out of suspension, falling towards the apex of the conical bottom, allowing for subsequent harvest and reuse, and for conditioning of the beer to take place in the same vessel.