Before a brewer starts making beer, the first step is to prepare the brewing grain. Unless they are malting their own barley, this involves milling or crushing the grains. This critical step can significantly influence the final product even before brewing begins. The goal is to crush the grains just enough to expose the starchy center of the barley seed while keeping the grain hulls intact. If the crush is too coarse, there won’t be enough starch converted into fermentable sugars. Conversely, if the crush is too fine, the husks—essential for creating a filter bed for the brew—will be damaged, leading to a gummy and unusable mixture.

After the grain has been milled, it’s added to a large vessel called the mash tun, where it is mixed with hot water to create the mash. This is where the magic begins. The heat from the water (known as liquor in brewing) activates the enzymes present in the barley, which then start converting the starches in the grains into sugars.

Since there are various enzymes in barley, each with its own preferred temperature range, brewers closely monitor the mash temperatures. By adjusting the temperature, brewers can control the types of sugars produced by these enzymes. Lower temperatures yield highly fermentable sugars, resulting in drier beers, while higher temperatures create sugars that are less digestible for yeast, leading to sweeter, fuller-bodied beers. The enzymes work rapidly; within about an hour, they finish converting starches into sugars. At this point, the brewer halts the enzymatic activity by raising the mash temperature above 200 degrees Fahrenheit, a process known as mashing out.

The next step in the brewing process involves separating the spent grain from the sugary liquid known as wort (pronounced "wert"). This procedure is called lautering.

To start lautering, the mash is transferred to a vessel with a false bottom called a lauter tun. Here, the clear wort is drained away from the grain hulls and barley grist. Additional water is also introduced during this stage to extract more fermentable sugars from the grains, a process known as sparging. Sparging must be done slowly to avoid disturbing the grain bed, which acts as a natural filter for the wort. Brewers typically add sparge water at the same rate that the wort is being drained. However, some traditional English brewing methods involve completely draining the wort before adding water and repeating the process. This second round of lautering is called second runnings and was historically used to produce small beers.

Brewers need to be cautious not to sparge for too long, as this can lead to the extraction of bitter tannins from the grains.

After the sweet wort has been separated from the grains, it is brought to a vigorous boil for one to two hours. This boiling process is crucial for several reasons. Historically, it sterilizes the beer, which was vital before modern sanitation practices. For centuries, people often mixed their clean and wastewater supplies, turning drinking water into a breeding ground for harmful bacteria. Although they didn't understand the science behind it, people knew that brewing made water safe to drink, which is why beer was consumed widely, even by children.

Boiling does more than sterilize the brew; it also impacts the hops. When hops are introduced to boiling water, they undergo a process called isomerization, which alters their molecular structure and releases bitterness into the beer. The longer the hops boil, the more alpha acids are isomerized, contributing bitterness to the brew. Hops added early in the boil, known as early hop additions, are typically boiled for an hour or more.

In contrast, hops added later in the boil primarily contribute flavor and aroma rather than bitterness. Hops contain volatile oils that break down quickly in boiling water, so to extract flavor, brewers usually add hops about 10-15 minutes before the boil ends. For aroma, hops are added even closer to the finish, sometimes just two minutes before the boil concludes, and often immediately after the boil.

Once the boiling process is complete, the wort is transferred to a whirlpool to separate any hop matter and coagulated proteins that have formed. It is then rapidly cooled, as quick cooling is essential to prevent oxidation, which can lead to off-flavors in the beer.

Once the wort has been cooled, it is transferred to a fermentor, typically a large stainless steel vat, though oak is sometimes used. Next, yeast is added, and the real excitement begins! From the moment the yeast is introduced, it starts consuming the sugars created during the mash. As the yeast feeds on the sugars, it produces carbon dioxide and alcohol, along with a variety of flavor compounds that can differ significantly based on factors like the yeast strain and fermentation temperature. The fermentation period can range from a few days for simple ales to over a month for lagers.

During fermentation, the brewer also determines whether to brew an ale or a lager, a choice that hinges on the type of yeast used. For ales, which encompass the majority of beer styles, the brewer pitches ale yeast and allows the fermentation temperature to rise to a cozy 65-76 degrees—ideal for ale yeast. This type of yeast, known as top-fermenting yeast, forms a thick, frothy layer called a kräusen or pellicle at the top of the fermentation vessel. While it may look intimidating, there's nothing harmful in the beer beneath it—aside from the alcohol, of course. This is one reason why home brewing is legal; the worst outcome is simply producing unpleasant-tasting beer!

In contrast, when brewing a lager, the brewer must maintain a cooler temperature, typically between 45 and 55 degrees. At these lower temperatures, lager yeasts, known as bottom-fermenting yeasts, work slowly and efficiently to create a clean-tasting beer with minimal yeast-derived flavors. Unlike ale yeast, lager yeast does not form a pellicle at the top of the fermentation vessel.

Once the yeast has consumed all the available sugars, primary fermentation is complete. However, the yeast's job isn't finished yet. Throughout fermentation, various off-flavors can develop alongside alcohol and carbon dioxide, including sulfur, butter, and green apple notes, often found in under-conditioned or “green” beer. Fortunately, with time, the yeast will absorb these off-flavors. For ales, this conditioning typically takes about a week, while for lagers—whose yeast tends to work more slowly—it can take several months. To expedite this process, some lager brewers practice kräusening, which involves adding still-fermenting wort (along with its yeast) to the conditioning beer to jumpstart flavor correction.

After fermentation is complete and the yeast has addressed the off-flavors, it becomes dormant and settles at the bottom of the fermentation vessel. This allows the brewer to easily remove the yeast, resulting in bright, clear beer. To further assist in this clarification process, many brewers use mechanical filtration or add filtering agents that help clump the yeast into larger groups, facilitating their quicker removal from suspension.

It's easy to overlook that the final step in brewing is packaging the beer. Fortunately, brewers don’t forget this step; otherwise, we might find ourselves drinking straight from large conditioning tanks (which, come to think of it, could be quite an experience). Packaging involves transferring the finished beer into containers for mass consumption, typically bottles, cans, and kegs. Most brewers also force carbonate their beer before packaging, allowing any CO2 produced during fermentation to escape into the atmosphere. This is crucial because without releasing the CO2, the tanks could become over-pressurized and potentially rupture.

Some brewers opt for bottle conditioning, where yeast and sugar are added to the beer after packaging, initiating a second fermentation inside the bottle. This process not only adds depth of flavor but also contributes to carbonation. Additionally, bottle conditioning can improve the beer's shelf life, as the yeast will consume any oxygen that seeps into the sealed bottle.