The brewing process
There is a great deal of science behind brewing. It's not essential for homebrewers to have an intimate knowledge of all the chemical reactions that happen during the various stages of beer production. However, it does help to have an understanding of what happens as a beer takes shape, even if you are just brewing with a can of concentrate and a kilo of sugar (but hopefully after visiting our site you will at least stop using sugar!).
Below is an outline of a simple brewing process, although there are many variations. We'll try not to bore you with too much science. If you want to understand the science of brewing there are myriad books and websites devoted to the subject.
Malted barley and other grains
Malted barley is generally regarded as one of the four essential ingredients — along with yeast, hops and water — needed to make beer. There are a handful of beers made without malted barley (usually gluten-free beers and some rare specialty beers) and many other grains can be used in brewing, but some type of malted barley usually makes up the majority of a brewer's "grain bill".
Raw barley can't be used as the base of a beer. It has to be malted then mashed to release its sugars, which the yeast can turn into alcohol.
Most commercial brewers and even the keenest homebrewer generally leave malting to the experts and buy barley that is already malted. It can, however, be done at home if you really want to. Malted grain is quite cheap, so you would only malt at home because you wanted to, not to save vast sums of money.
Barley and many other grains store their sugar in the form of insoluble starch. The malting process involves moistening and warming the grain so that it germinates. Germination produces an enzyme that will be used later in the brewing process to convert the starch in the grain to sugars. Just as the grain begins to sprout, the grain is heated to dry it, stop germination and kill the seed. The grain is now malt.
The more the grain is heated the darker it will be and the more colour it will impart to the beer in which it is used. Most malt is only heated to dry it out and sometimes to add a little colour. If the malt is heated sufficiently the enzyme in the grain will be destroyed as the grain takes on a darker colour, meaning that the grain can only be used for adding flavour and aroma to beer, not fermentable sugars.
To extract the sugar, the malt is mashed. During this process, the malt is soaked in warm water (perhaps strangely, the water is called liquor) and held at somewhere between the low 60s and low 70s celcius (about 140°F to 160°F) for up to two hours while enzymes produced during the malting of the grain convert the grain's starch to fermentable sugars. Different temperatures during mashing produce different proportions of fermentable and unfermentable sugars. Mashing at the lower end of the temperature scale encourages an enzyme called beta amylase to convert the starches to sugars. Beta amylase produces a sugar that is more easily fermentable by the yeast and therefore results in a beer with a relatively light, dry body. An enzyme called alpha amylase works best at higher temperatures and produces more unfermentable sugars, meaning the resulting beer will have more body and residual sweetness.
If the mash temperature is too low the enzymes in the grain will not convert the starches to sugar, while if the mash temperature is too high the enzymes will be killed and the conversion will also not take place.
Other unmalted and malted grains are added to the mash to extract their sugars and/or flavours. For example, very dark malts that give stout its colour and roasted flavour are mashed with all the other grain even though they do not contribute any fermentable sugars to the brew, which comes mainly from a relatively light-coloured malted barley.
There are two methods of mashing. The most widely used is called an infusion mash, in which the warm water and malt are added to a vessel and left there for the entire mash period. Infusion mashes can be divided into two types: single-step infusion mash, in which the mash is held at the same temperature for the whole mash, and a stepped mash, in which the mash temperature is raised in stages — or "rests" — through the mash. One reason a stepped mash may be done is to begin about 50C for a "protein rest". A protein rest breaks up proteins that can cause haze in the finished beer and prevents gummy mashes, both of which can occur when large proportions of unmalted wheat, barley, rye or oats are used. A protein rest is also needed to break down proteins when brewing with moderately modified malts, which have intentionally not been fully malted. However, most modern malts are fully modified and do not require a step mash. After the protein rest the mash temperature is raised to a temperature at which the amylase enzymes will convert starch to sugars.
The second mashing method is decoction, in which a portion of grain is removed from the mash, boiled and returned to the main mash vessel to raise the mash temperature. The boiling slightly caramelises some of the sugars in the grain and liquid. Decoction mashing is time-consuming and fiddly. Many people feel that modern malting methods render decoction mashing unnecessary, while others argue that some styles of beer, particularly pilsners, demand a decoction mash.
Other grains can also be malted and used to make beer. The most common malted grain apart from barley that is used in beer production is wheat.
Some grains — for example rice and corn — do not contain the necessary enzyme to convert their starches into sugars during mashing and must therefore be mashed with other grain, usually barley or wheat, so that it can "borrow" some of its enzymes.
The ability of a malt to convert starch to sugars via the enzymes it contains is known as "diastatic power". Base malts, which are light in colour and make up most of the grain bill, have a high diastatic power while other grains, for example chocolate malt, have a diastatic power of 0 (i.e. none). That doesn't matter, because the high diastatic power of the base malt will make up for low or no diastatic power in other malt or adjuncts such as rice and corn.
Unmalted grain can be added to the mash, but it will not contribute sugars but add characteristics such as taste, aroma and body, or aid head retention.
Another type of grain that can be added to beer is crystal malt, also known as caramel malt. To make crystal malt, regular malt is wetted and heated so that in effect the mashing process takes place within the grain. For this reason, crystal grain does not need to be mashed in order to release its sugars, although in all-grain brewing it is always added to the mash. The sugar can simply be extracted by steeping in warm water, so if you're a "kit and kilo" brewer looking to start adding grain to your beer, crystal malt is a good place to start. For more information see the page on adding hops and grain.
After the grain has been mashed, the sweet liquid is drained off the grain slowly, and in a process known as sparging the grain is rinsed gently in warm water to extract the last of the sugars. The "spent" grain, which has now released its sugars into the wort, is then disposed of, often as animal feed.
Sparging is important for commercial brewers because it extracts the last remnants of sugar from the grain. However, some all-grain homebrewers do not bother and employ the "no-sparge" method of brewing because it makes brew day simpler and quicker, and usually requires less equipment. As well, the expense of the slightly greater amount of grain to compensate for no-sparge is insignificant for homebrewers, while for commercial brewers the costs would be significant. The "brew in a bag" homebrewing technique is typically no-sparge.
Read more about mashing and sparging at Wikipedia.
After the liquid is drained from the "spent" grain, it is brought to the boil and other ingredients, usually hops but perhaps other ingredients such as honey or herbs and spices, are added. Hops give beer its distinctive bitter flavour, and also contribute flavour and aroma in varying degrees depending on the variety of hop and when they are added to the boil.
Hops added near the start of the boil will contribute more bitterness and much of their aroma and flavour will boil off, while the further towards the end that hops are added the more they will contribute to the flavour and aroma. Indeed, hops are added to some beers when the heat is turned off (at flame-out) or even during fermentation, maturation or kegging to maximise the aroma that would otherwise be driven off if they were boiled.
At the end of the boil the mixture is cooled and drawn off into a fermenter, ready for the yeast to be added. A sediment called "trub" — a mixture of proteins, hops and other particles generated during the boil, are left behind and discarded.
A lot of water or energy, or both, is required to cool a large volume of liquid, so some homebrewers employ the "no-chill" method, which involves leaving the boiled liquid in the kettle (boiling vessel) or transferring it to a fermenter or plastic "cube" to cool. A cube is a sealable container such as a food-safe plastic jerry can that can be sealed tightly with little or no head space for air. The cube can be left to cool naturally and the liquid can be put in a fermenter and the yeast added at any time, even weeks or months later.
The unfermented beer is called "wort".
Yeast and fermentation
Yeast is a living micro-organism that loves nothing more than to consume sugars and turn them into alcohol and carbon dioxide in the process known as fermentation. Wild yeast and other micro-organisms also love consuming sugar, so it is important to cool the wort to the correct temperature and "pitch" the yeast as soon as possible after the boil. The exception to this is the "no-chill" homebrewing method described above in which the wort is left to cool naturally. At the time of pitching or during the fermentation, if the temperature is too low the yeast will become dormant and not complete its work, while if the temperature is too high the yeast will be killed. Most yeast will convert sugars to alcohol very quickly at temperatures up to the high 30s celcius. However, fermentation at high temperatures will produce undesirable flavours and aromas. In general, the ideal temperature for brewing with an ale yeast is about 18°C to 20°C or 22°C, while for a lager yeast it's 9°C to 12°C. Ale yeasts will become dormant at temperatures at which lager yeasts are still fermenting.
There are, however, some exceptions to this rule, with some lager yeasts being used at ale temperatures, ales being fermented cooler than usual and some beers being fermented in the high 20s.
Once the yeast has converted all the sugars it can to alcohol and carbon dioxide, it drops out of suspension over the course of several days and forms a thick layer on the bottom of the fermentation vessel.
Towards the end of fermentation some brewers transfer the beer to another vessel because they believe that the beer sitting on the layer of yeast can affect the flavour. Some homebrewers swear this process, called "racking", is essential to producing top-class beers, while others believe it's a waste of time. If done properly and carefully, racking will do no harm.
Maturation, bottling and kegging
Most large brewers and some small ones filter the yeast and other particles out of the beer almost as soon as fermentation has ceased then package it for distribution.
However, the traditional method, and the one employed by most homebrewers, is to leave the beer once fermentation has finished, either in the fermentation vessel or in another vessel after racking. During this time, usually at least a week, undesirable flavours are broken down, improving the flavour of the beer, and the yeast will drop out of suspension, clearing the beer.
The beer can be bottled, canned or kegged at this stage, or matured further. The best-known type of maturation is lagering (lager is German for "to store"), which involves holding the beer at a temperature close to freezing for between a week or so and several months. During this time further undesirable flavours dissipate and the beer takes on a more rounded flavour.
There are two ways that beer can get its bubbles: naturally or artificially.
With natural carbonation, also known as bottle or keg conditioning, the beer is transferred to the bottle or keg along with a small amount of sugar (in a process known as priming) or another beer that is still fermenting (this is known as krausening). Because this introduces a small quantity of fermentable sugar, the yeast consumes this and produces alcohol and carbon dioxide. The bottle or keg is sealed and the carbon dioxide cannot escape so dissolves into the beer. When the beer is served the carbon dioxide comes out of solution in the form of bubbles.
Bottle conditioning is the method most homebrewers use if they bottle beer, and some also use it if they keg their beer.
Some breweries filter or pasteurise their beer before bottle or keg conditioning, which removes any yeast. They then add some sugar and more yeast (in some cases a different strain) to do the carbonation.
Naturally carbonated beers need to be left for at least a few weeks for the yeast to consume the sugar and carbonate the beer, and for the beer to mature. In fact, some bottle conditioned beers, Coopers ales from South Australia, for example, have a "best after" date rather than a "best before".
Artificial carbonation, known as forced carbonation, involves injecting carbon dioxide under pressure to the beer so that it dissolves into the liquid. The beer is then bottled or kegged and when the pressure is released the carbon dioxide comes out of suspension as bubbles. Homebrewers with keg setups usually force carbonate their beer in the kegs although some also use natural carbonation. Many commercial breweries and some homebrewers filter their beer before they force carbonate. Some breweries pasteurise rather than filter their beer, but this is not an option for homebrewers because of the equipment required.
If a beer is force carbonated it can be drunk immediately it is carbonated.