(This is part two of a two part article that began with How beer is made - Malting and Brewing)
At this point, the stuff in the tanks is called bright beer. The yeast converted the wort into beer but, it is not quite ready to drink. It needs to be carbonated and packaged before it can be called beer so, for the moment, its bright beer. The bright beer is held in tanks for a resting period that can last anywhere from a week or two to several months depending on the brewer and the style of beer. Ales tend to get a shorter rest period while lagers can wait for months. The name, lager, actually comes from the German word for long and refers directly to this long period of waiting in cool, dark environments. This aging period does two things. First, it somewhat filters the beer as heavier solids fall out of the beer and settle on the vessel floor. Second, it ages the beer, mellowing and maturing the flavors. Even if it only lasts a couple of weeks, this period is vital to producing a properly balanced brew.
Finally comes carbonation and packaging. Earlier, I mentioned that not all of the CO2 that results from fermentation is allowed to escape through the airlocks. During this step, most breweries trap a small amount of CO2 with the beer where it gets absorbed in the liquid, thus carbonating the beer. Since the beer is long past the carbonation stage, this is done by kicking off a small bit of additional fermentation. There are a couple of ways of pulling this off. First is that by counting on the viable yeast still suspended in the beer, brewers will add just a bit of sugar then sealing the beer either in its final package of a bottle, cask or keg or in a larger vessel, not unlike the fermentation vessels then plugging up the airlock. The second way is to steal some actively fermenting wort from a freshly brewed batch then similarly sealing it. In both cases, the additional ingredients must be precisely measured. Add too little and you've got a flat beer; add too much and you've got exploding bottles!
A third method of carbonation exists called forced carbonation. Instead of relying on the byproduct of fermentation, brewers using forced carbonation directly inject CO2 into a sealed container with the beer and forcing the beer to absorb it. Not many brewers use forced carbonation.
I doubt I need to tell you much about packaging. Bottles, cans, and kegs hold most of the beer we drink and, therefore, most of us have held them.
This is an incredibly simplified description of the brewing process. When you visit the various breweries you can see how different breweries do it. Even if you do not like the beer made at a particular brewery, do not let that be a reason not to visit it. For example, I actively recommend casual beer drinkers and beer geeks alike that, when visiting St. Louis that they check out two breweries - Anheuser-Busch and O'fallons. AB's massive, industrial brewing operation is impressive to tour. Visitors get a peek at brewing at an assume scale and how industrial brewing work. After that, a tour of O'fallon quite a bit different but no less instructive. Visitors can stand in one spot on the brewing floor and see every piece of equipment necessary to make beer. The tour will be led by one of the guys who actually makes the beer so you can ask anything you want and really understand the process. Visiting different breweries of all shapes and sizes will give you a great picture of how beer is made.