How Beer Works

As we learned in the introduction, there are four main ingredients in beer: barley, water, hops and yeast. Each has many complexities. We'll start with malted barley.

Malted Barley

Barley is the seed of a grain that looks a lot like wheat. Before barley can be used to make beer, it must be malted, which involves a natural conversion process.

First, the barley must be allowed to germinate, or start to sprout. This is done by soaking the barley in water for several days, and then draining the barley and holding it at about 60 degrees Fahrenheit (15.5 C) for five days. This allows the husk to open and barley to start to sprout -- at this point it is called green malt. Like all seeds, the barley contains nutrients that can sustain the growing seed until it can produce its own nutrients using photosynthesis. During the germination process, enzymes released by the plant convert these nutrients (which are starches) into sugars that can feed the plant while it grows. The key to the malting process is to stop the germination of the barley at a point when the sugar-producing enzymes are present but most of the starch is still unconverted. Eventually, these enzymes will produce the sugars that will feed the yeast to make the alcohol in the beer.

After this natural process has released the enzymes, the green malt is dried by gradually raising the temperature. The intensity of the malt flavor and color depends on how high the temperature is raised during the drying process. One final step must be completed -- removing any small roots that formed during germination -- and the malted barley is ready to begin the brewing process. Most breweries buy barley that has already been malted to their specifications.

Hops

The hops used to make beer are the flower of the hop vine, which is a member of the hemp family (Cannabaceae). Hops are closely related to another member of the hemp family that you may have heard of -- cannabis, or marijuana, although hops do not have the psychoactive effects associated with marijuana.

Hops contain acids, which give beer its bitterness, as well as oils that give beer some of its flavor and aroma. Adding hops to beer also inhibits the formation of certain bacteria that can spoil the beer.

There are many different kinds of hops, each of which gives a different taste, aroma and amount of bitterness to the beer it is used in. In the United States, hops are grown mainly in Washington state. Hops are also grown in Germany, Southern England and Australia.

Yeast

Yeast is the single-celled micro-organism that is responsible for creating the alcohol and carbon dioxide found in beer. There are many different kinds of yeasts used to make beer; and just as the yeast in a sourdough starter gives sourdough bread its distinctive flavor, different types of beer yeast help to give beer its various tastes.

There are two main categories of beer yeast: ale yeast and lager yeast. Ale yeast is top fermenting, meaning it rises near the surface of the beer during fermentation, and typically prefers to ferment at temperatures around 70 F (21 C). Lager yeasts are bottom fermenting. They ferment more slowly and prefer colder temperatures, around 50 F (10 C).

The Mash

The mash is the process that converts the starches in the malted barley into fermentable sugars. At the Carolina Brewery, they start by crushing the malted barley between rollers to break up the kernel.

There is a fine tradeoff in the rolling process: the more the kernel is broken up, the more sugars can be extracted from the grains; but if it is broken up too much, the husk that surrounds the kernel may get broken down, which can cause a stuck mash. If the kernel is broken up just enough, then when the mash is finished, the whole husks form a filter bed that captures any solids from the liquid; but if the husks are broken down too much, they clog up and don't let the liquid through -- a stuck mash.

Next, the crushed grains pass through a feed pipe into the mash-lauter-tun. This insulated vessel has a device called a hydrator, which sprays heated water onto the grains as they enter. This eliminates any dry spots in the mash -- dry spots mean wasted sugars. The wet grains stay in the mash-lauter-tun for an hour. Since the vessel is insulated, the temperature stays at around 150 F (65 C).

The purpose of the mash is to convert the starches in the malted barley into fermentable sugars to be used in the next step of the brewing process. Starches are strings of many glucose molecules chained together -- these chains must be broken down into chains of only two or three glucose molecules before they can be fermented. We learned earlier that the malted barley contains enzymes, which can convert the starches.

There are two different types of enzymes in the malted barley: alpha-amylase and beta-amylase. The alpha enzymes break up the long chains of starches by splitting them in half. The beta enzymes break down the starches by chopping them off a couple at a time from the ends of the chain. Only if these two enzymes work together can the conversion be accomplished in a reasonable amount of time. There is a catch though: The alpha enzymes are most active at 149 to 153 F (65 to 67 C), and the beta enzymes are most active at 126 to 144 F (52 to 62 C). So the temperature and duration of the mash must be carefully controlled to get a good conversion.

The last steps needed to complete the mash are lautering and sparging. The liquid is drained from the bottom of the mash-lauter-tun and then recirculated to the top so that it is filtered through the husks of the spent grains. Additional heated water is then poured over the grains -- a process called sparging -- to make sure all of the sugars are removed.

The mash is an amazing process. Before the mash starts, the grains don't taste at all sweet, but the liquid that is drained off from the grains at the end of the mash is very sweet and sticky. This liquid, which now contains mostly fermentable sugars, goes on to the boil.

The Wort

The next step in the beer brewing process is called the boil. At the end of the boil we will have a finished wort (pronounced wert).

To start, the liquid from the mash is put into a huge brew kettle. The one used at the Carolina Brewery holds more than 600 gallons (2,270 L). It is a steam jacketed brew kettle. This kettle has double walls with a gap between them through which steam is circulated. This provides very even heating, since both the bottom and the sides are heated. The temperature is raised until the liquid comes to a vigorous rolling boil, and it is held there for 90 minutes.

At the beginning of the boil, hops are added. These are called the boiling hops, and their job is to add bitterness to the beer. The acids that produce bitterness in the beer are not easy to extract from the hops, which is why they need to be boiled for up to 90 minutes. The oils that produce the hop flavor and aroma are very volatile and evaporate quickly, so the boiling hops only contribute bitterness to the beer -- the flavor and aroma are added later.

Depending on what type of beer is being brewed, more hops may be added near the end of the boil -- these are called finishing hops. Generally, hops that are added about 15 minutes before the end contribute flavor to the beer. Hops added just a few minutes before the end contribute aroma to the beer. The oils in the hops that give the beer a distinctive hop smell are the most volatile, so these hops really just need to steep in the hot wort for a few minutes, like tea leaves, to extract the oils. Some of the beers brewed at the Carolina Brewery get finishing hops added at three different times. In order for each batch of beer to taste the same, exactly the same amount of the same type of hops must be added at exactly the same time during each boil.

In the next section, we'll see the next step in the brewing process.

Before the wort can go on to the next step, all of the solids must be separated from the liquid. This is done in a very neat way. The wort is pumped from the kettle, and forced back into the kettle through a jet nozzle. This flow of liquid causes a whirlpool to form; and if you've ever stirred tea leaves in a cup, you know that they move to the center of the whirlpool. When this whirlpool forms in the brew kettle, all of the hops and other solids move to the center. The pump is then turned off, and over the next 20 minutes the whirlpool gradually stops and the solids settle to the bottom, forming a fairly solid cone.

When the wort is drained, the solids stay in the kettle. Next, the wort must be cooled down to the proper temperature for the yeast. This is done in a liquid-to-liquid heat exchanger. The wort is circulated through one set of tubes while chilled water is circulated through another set. The tubes with hot wort running through them transfer heat to the tubes holding the chilled water.

The cooling water is chilled first, so that the volume of water that is required to cool down one entire batch of wort is about equal to the volume of wort. The cooling water ends up at a temperature of about 170 F (76 C), and is stored in an insulated tank and used to brew the next batch of beer. This way both the water and the heat energy are saved.

It is important to cool the wort quickly so that the yeast can be added right away and fermentation can begin. This reduces the chance of contamination by stray yeasts floating around in the air.

Fermentation is the process by which yeast converts the glucose in the wort to ethyl alcohol and carbon dioxide gas -- giving the beer both its alcohol content and its carbonation. To begin the fermentation process, the cooled wort is transferred into a fermentation vessel to which the yeast has already been added. If the beer being made is an ale, the wort will be maintained at a constant temperature of 68 F (20 C) for about two weeks. If the beer is a lager, the temperature will be maintained at 48 F (9 C) for about six weeks. Since fermentation produces a substantial amount of heat, the tanks must be cooled constantly to maintain the proper temperature.

These fermentation tanks hold more than 2,400 gallons (9,085 L), which means that it takes four batches of wort to fill one tank. Since fermentation takes at least two weeks, the capacity of the brewery is limited by how many tanks they have.

When the wort is first added to the yeast, the specific gravity of the mixture is measured. Later, the specific gravity may be measured again to determine how much alcohol is in the beer, and to know when to stop the fermentation.

The fermenter is sealed off from the air except for a long narrow vent pipe, which allows carbon dioxide to escape from the fermenter. Since there is a constant flow of CO2 through the pipe, outside air is prevented from entering the fermenter, which reduces the threat of contamination by stray yeasts.

When fermentation is nearly complete, most of the yeast will settle to the bottom of the fermenter. The bottom of the fermenter is cone shaped, which makes it easy to capture and remove the yeast, which is saved and used in the next batch of beer. The yeast can be reused a number of times before it needs to be replaced. It is replaced when it has mutated and produces a different taste -- remember, commercial brewing is all about consistency.

While fermentation is still happening, and when the specific gravity has reached a predetermined level, the carbon dioxide vent tube is capped. Now the vessel is sealed; so as fermentation continues, pressure builds as CO2 continues to be produced. This is how the beer gets most of its carbonation, and the rest will be added manually later in the process. From this point on, the beer will remain under pressure (except for a short time during bottling).

When fermentation has finished, the beer is cooled to about 32 F (0 C). This helps the remaining yeast settle to the bottom of the fermenter, along with other undesirable proteins that come out of solution at this lower temperature.

Now that most of the solids have settled to the bottom, the beer is slowly pumped from the fermenter and filtered to remove any remaining solids. From the filter, the beer goes into another tank, called a bright beer tank. This is its last stop before bottling or kegging. Here, the level of carbon dioxide is adjusted by bubbling a little extra CO2 into the beer through a porous stone.

The most important thing about the bottling and kegging process is to keep the beer from being contaminated by stray yeasts, and to keep oxygen away from the beer. These are the main things that can reduce the shelf-life of beer.

The ways that the beer is transferred into bottles and kegs is pretty similar; but bottling has a few extra steps, so we'll talk about bottling.

The bottling line at the Carolina Brewery can fill up to 100 12-oz (355 ml) bottles of beer every minute. To start the process, the empty bottles are loaded onto the bottling line, where they are first rinsed with a chlorine solution, and then blasted with CO2 to remove the solution.

Next, the bottles enter a turret-like mechanism that can hold 12 bottles at once. Each bottle rides around the turret once. During its ride, the bottle is purged with CO2 several times before it is filled. The bottles are pressurized with CO2 so that when the beer is forced into the bottles under pressure it doesn't foam up too much. After the beer has been added to the bottles, the pressure is slowly relieved until the beer is at ambient pressure. As each filled bottle leaves the turret, an empty one takes its place.

Next comes the capping machine -- but now there is a little bit of air space at the top of the bottle that needs to be purged. To do this, the bottle is passed under a very narrow, high-pressure jet of water that hits the beer, causing it to foam up and drive the air out of the bottle. The cap is then applied before any air can re-enter the bottle.

After the cap is applied, the outside of the bottle is rinsed to remove any beer that may have foamed out during the process.

Surprisingly, the most difficult part of the bottling process is applying the label to the bottle. Getting a label to stick to a cold wet beer bottle is no easy trick.

The labels are fed into the labeling machine, which has a spinning device that rolls glue onto the labels and then sticks them to the bottles as they pass by. If all goes well, the label will be properly positioned, smooth and well-adhered.

A special inkjet printer squirts the date onto the label as it moves past the print head. The date the beer was bottled and also a "best before" date (three months after the bottling date) are printed on the label.

Homebrewing

If this all sounds very complicated, then you might be wondering how people ever manage to brew their own beer. But as you may have gathered, most of the complexity of the brewing process is due to the need for a commercial brewery to turn out beer that tastes exactly the same batch after batch, year after year.

Most homebrewers have no such requirement -- it doesn't matter if the beer tastes exactly the same each time they make it. There are so many different types of beer to brew that many homebrewers never make the same type of beer twice anyway.

At homebrewing stores (see the links on the next page) you can buy malt extract, which is the fermentable sugars extracted from the mash. That eliminates one fairly complicated step (although it is entirely possible to do a mash in your home). A basic set of homebrewing equipment consists of:

All of these supplies and any ingredients you need are available at homebrewing stores, and are sometimes packaged as a kit.

For more information on beer, homebrewing and related topics, check out the links on the next page.