Greetings! Here's my attempt at creating an introduction to beer brewing. Please feel free to point out errors, inaccuracies, missing info, or anything you feel should be different.
Disclaimer: written under the influence of homebrew
Ingredients
In its most basic form, alcoholic fermentation is just yeasts chomping away at sugars to generate alcohol and carbon dioxide, giving our favourite beverage the buzz and fizz we enjoy. Depending on yeast strain and conditions (temperature, OG - that is initial or original gravity of the wort, nutrient availability), it may be more or less potent (in terms of alcohol tolerance) or yield more or less flavour compounds. Yeast suppliers usually give datasheets with temperature ranges and alcohol tolerances for yeasts.
Malt is just grain that has been coerced into sprouting then dried. This unlocks enzymes within the grain that cut up complex sugars (starch) stored inside the grain into simpler sugars that the seedling would use as its initial energy stores. The drying conditions of the malt are what give us the large selection we have today. Do note, however, that the darker the malt, the less enzymatic activity it has.
The main preservative in beer - hops inhibit lactobacilli that turn beer sour and give it the aroma we all know and love. Hops are defined by their alpha-acid content, which turn into beta-acids (that give beer its hop bitter taste) during boiling. The time of addition for hops is key for this, as longer boiling yields more beta-acids but loses flavour from the hops - hence, bittering hops are boiled for longer, aroma hops are boiled for less or not at all - added at whirlpool or used to dry-hop. Hops are also sensitive to oxidation, so they're stored in the freezer and sold in vacuum-sealed bags. There is a plethora of hops available from any self-respecting homebrew store and hop pellets (ground up and compressed hop flowers) are by far the most common form.
Without going into much detail, brewing water should not be overlooked. The ionic content of water does influence your beer quite a lot (for instance due to pH or presence / absence of magnesium ions that may bring out hop bitterness). Historically, brewing water has been tied to specific styles (like dry irish stout in Dublin, IPAs in Burton-on-trent or pilsners in Pilsen). Water used for brewing must, however, be chlorine-free, in order to avoid unpleasant flavours. This can be accomplished by using 1-2 campden tablets to 20L (~5 gal) water or filtering your water throught activated charcoal before use.
Process
- Sanitizing
The most important step in brewing - sanitizing stuff. Everything that does not get heated to at least pasteurization temperatures (~71 C or 161 F) needs to be sanitized. Everything that touches the wort after it's cooled or fermented beer needs to be sanitized. This cannot be stressed enough. Using StarSan diluted to its specification for about 30 seconds usually does the job. If something was sanitized and it touches something that was not, it needs to be sanitized again. Seriously, don't take this step lightly.
- Mashing
Involves keeping your mash (the mixture of crushed, malted grains and water) at a specific temperature for a specific amount of time in order to transform the starch in the grains into simpler sugars that yeasts can digest. Some usual conditions would be 63-66 C (145-150 F) for one hour - these give a good balance of body and fermentability. More advanced brewers (or those posessing more advanced equipment) may do step mashes. The temperatures are selected in order to favour different enzymes present in the malt. A mash-out step is usually just heating the mash to 78 C (172 F) - this preserves just a bit of enzymatic activity - alpha-amylase (the one responsible for body) stops working around this temperature.
Regarding water:grain ratio, I personally use around 6 kg (12 lbs) to 23 L water (6 gal).
At the end of mashing, the liquid has to be separated from the solids by either transferring through a sieve (mash tun to boil kettle) or removing the solids (like the case for brew-in-a-bag or all-in-one systems - Braumeister, Grainfather).
- Sparging
Sparging involves pouring water heated to the mash-out temperature over the spent grain in order to extract any lingering bit of sweetness that did not make it to the boil kettle. (I have no idea how you would do this when using brew-in-a-bag, though - edit: apparently you don't, problem solved :) ).
(Extract brewers will usually skip the steps above and just dissolve the extract in water then proceed to the boil)
- Boiling
The purpose of boiling is two-fold. First, to remove dimethylsulfide, or DMS, a compound obtained during mashing that has a vegetable-like flavour usually undesireable in beer. The other purpose is to extract compounds from hops and convert them from alpha- (aromatic) to beta-acids (bitter) to provide bitterness, aroma, and preservative qualities to the beer. (It also concentrates the wort.)
Boiling usually takes 1 hour (as that is the amount of time that usually removes all the DMS). The boil can be longer if one wishes to concentrate the wort further.
Timing and quantities of hop additions are very important to the final hop flavour profile of the beer. The more hops are boiled, the more aroma they lose and the more they impart bitterness to your beer.
- Chilling, transfer to fermenter and pitching yeast
Once the wort is done boiling, it is cooled (usually by applying cold water through a cooling implement - jacket or wort chiller), transferred to the fermenter and the yeast is added (or pitched). The simplest way of doing this is to add the dry yeast directly over the wort. Everything that touches wort after chilling must be sanitized (refer to step 0) - this includes the outside of the yeast packet before opening it.
Gravity readings (OG, original gravity) are taken of the cooled wort using a densimeter or refractometer.
- Fermentation
The fermenter is placed in conditions adequate for the beer style being prepared and the yeast being used (lagers in cold conditions, ales a bit warmer, saisons or kveik yeasts in even warmer conditions) - check the yeast for information on temperatures, fitted with an airlock. When the airlock no longer significantly bubbles (or better yet, the gravity of the wort is where one would expect it to be based on recipe), fermentation is done. I just eyeball it and when I get 1-2 air bubbles / minute in the airlock, I declare it done. YMMV.
- Bottling or kegging
Refer to step 0. Yes, sanitize all bottles. Sanitize that keg. Sanitize your hands and the racking cane. Then sanitize your hands again. Are your hands sanitary? Better do it again, just to make sure.
In order to get carbonation in the finished product, table sugar can be added based on style and carbonation preferences to the finished beer before bottling. The yeast left over in the solution will take care of the rest. A good starting point would be 4-5 g/L of table sugar (or 0.5 to 0.66 oz/gal). I usually add it as syrup made by dissolving the sugar in water, boiling, cooling (covered - refer to step 0) and mixing the whole sugar with the whole batch of beer. Then transfer to bottles or keg, and wait 1-2 weeks. Chill, and serve.
If kegging, you can also force carbonate by adding beer and pressurizing with carbon dioxide for about a week or so.
- Cleaning
Cleaning and sanitizing are the most important steps in brewing. Clean equipment is easier to sanitize. Sanitized equipment is less likely to give you any contamination. While contamination can just sour your beer, it may also cause exploding bottles.
Some great advice from the comments:
On sanitation and RDWHAHB
Feedback is welcome, and will edit this post as required. Cheers!
legend goes that Greta made the guy mad on xitter and he posted a response that also included a picture of himself with a pizza box, and cops knew where to find him because of the brand on the box, but not sure if it was proven true or not