Homebrewing can be many things. People enjoy it as a hobby, an art, a career starter, a money saver and much more. It's a simple process that can be turned into as complex a process as one desires. The science is simple:
- 1. Malted grain* (usually barley) has it's starches extracted and converted into fermentable sugar. This sugar can be extracted by the homebrewer, or bought pre-extracted in Dry Malt Extract or Liquid Malt Extract. If using extract, the brewer will often steep some specialty grains in some water before the boil in step 2. Specialty grains add flavor, color and body to the beer. This is one way different beers are made: using different grains in unique combinations.
2. The extracted sugars are then boiled with hops: A plant which adds bitterness, flavor and aroma to the beer. The longer they are boiled, the less flavor and aroma, but more bitterness will be extracted. There is usually at least 1 bitterness and 1 flavor/aroma addition per brew. Hops can come in whole leaf (right off the plant and dried) or pelletized forms.
3. The liquid, now called "Wort (pronounced: Wert)" is added to a fermenter. This can be anything from a food grade plastic bucket to a glass carboy.
4. Yeast is then thrown on top of the wort and the fermenter is sealed except for a one-way airlock in the lid that allows carbon dioxide (CO2) to be released, but does not allow the outside air to come back in. CO2 and alcohol are the by-product of yeast when they eat sugar. The sugar is broken down into CO2, which is released as a gas and and the alcohol is left in the wort which in turn creates beer. That is the fermentation process.
5. After some time, when fermentation is complete, the beer is added to bottles or a keg. The time differs depending on the beer style. A rule that can be applied to most beers is 1 week in the primary fermenter, 2 weeks in a secondary fermenter to clear and mature, then 3 weeks in bottles to carbonate and finish maturing. This is the 1-2-3 rule. But some beers, like stouts and hefeweizens can be ready to drink in 2 weeks or less.
6. When the beer is added to bottles, you add a little extra sugar so that the leftover yeast can ferment in the bottles. Since there is no one way airlock for the CO2 to be released, the CO2 gets absorbed into the beer and it becomes carbonated. If adding beer to a keg, you can do the same process or you can force carbonate it with a CO2 tank.
This is just a basic overview. Most starter kits come with good instructions, and if you really want to learn all about brewing http://www.howtobrew.com is a great online source. It's a complete book teaching how to brew. And, of course, don't be afraid to ask any questions on this forum!
*Malted grain is produced when the seeds of a certain grain are germinated then kilned. This process produces starches (complex sugars).