Barley is used to make brewers' malt. At the malting companies, barley is soaked, germinated (sprouted), then dried and/or kilned/roasted to arrest further growth. During the period of controlled growth in the malting plant, specific barley enzymes are released to break down the membranes of the starch cells that make up most of the kernel. But these are internal changes only; apart from a slight change in colour, the external characteristics remain essentially unchanged. When the malt leaves a malting plant, it still looks like barley.
Malt is added to heated, purified water and, through a carefully controlled time and temperature process, the malt enzymes break down the starch to sugar and the complex proteins of the malt to simpler nitrogen compounds. Mashing takes place in a large, round tank called a "mash mixer" or "mash tun" and requires careful temperature control. At this point, depending on the type of beer desired, the malt is supplemented by starch from other cereals such as corn, wheat or rice.
The mash is transferred to a straining (or lautering) vessel which is usually cylindrical with a slotted false bottom two to five centimetres above the true bottom. The liquid extract drains through the false bottom and is run off to the brew kettle. This extract, a sugar solution, is called "wort" but it is not yet beer. Water is "sparged" (or sprayed) though the grains to wash out as much of the extract as possible. The "spent grains" are removed and sold as cattle feed.
After the beer has taken on the flavour of the hops, the wort then proceeds to the "hot wort tank". It is then cooled, usually in a simple-looking apparatus called a "plate cooler". As the wort and a coolant flow past each other on opposite sides of stainless steel plates, the temperature of the wort drops from boiling to about 10 to 15.5 °C, a drop of more than 65.6 °C, in a few seconds.
The wort is then moved to the fermenting vessels and yeast, the guarded central mystery of ancient brewer's art, is added. It is the yeast, which is a living, single-cell fungi, that breaks down the sugar in the wort to carbon dioxide and alcohol. It also adds many beer-flavouring components. There are many kinds of yeasts, but those used in making beer belong to the genus saccharomyces. The brewer uses two species of this genus. One yeast type, which rises to the top of the liquid at the completion of the fermentation process, is used in brewing ale and stout. The other, which drops to the bottom of the brewing vessel, is used in brewing lager.
For one to three weeks, the beer is stored cold and then filtered once or twice before it is ready for bottling or "racking" into kegs.
In the bottle shop of a brewery, returned empty bottles go through washers in which they receive a thorough cleaning. After washing, the bottles are inspected electronically and visually and pass on to the rotary filler. Some of these machines can fill up to 1,200 bottles per minute. A "crowning" machine, integrated with the filler, places caps on the bottles. The filled bottles may then pass through a "tunnel pasteurizer" (often 23 metres from end to end and able to hold 15,000 bottles) where the temperature of the beer is raised about 60 °C. for a sufficient length of time to provide biological stability, then cooled to room temperature.