So Yeah, Dood #12: Conditioner
Most actual fermentation occurs in the first week to ten days after yeast is added to the wort. Depending on the style of beer, brewers tend to siphon, or rack, the resultant beer into a secondary fermenting vessel.
If a brewer wants to clear a beer following fermentation, he will usually transfer beer that has reached its expected final gravity from the primary fermenter to a secondary fermenter. Doing this, the brewer can siphon, or rack off of the spent yeast cake that has settled to the bottom of the primary fermenter. If he happens to make the same beer, he can use the spent yeast instead of re-pitching from a new starter, though usually brewers will only do this one time to avoid significant changes in the yeast strain.
Flavoring agents are usually added during secondary fermentation. For instance, if you want a raspberry flavored ale, you would pour raspberry purée into the empty secondary fermenter, and then rack the beer onto the fruit and let it soak up the raspberry essence for between ten dasy and two weeks.
By cooling the second fermenter, suspended particles of yeast, grain dust, flakes of coagulated proteins, and other bits will fall to the bottom of the new fermenter where they can be left behind when bottling or kegging. This process is called lagering, but doesn’t necessarily make the final product a lager. Lager in German literally means “to store.” True lager beers are often lagered at near freezing temperatures; often for lengthy periods of time in order to fully clear a beer of particles and stronger yeast-produced flavors.
Beer is not carbonated at this point in the process. While yeast produces carbon dioxide throughout fermentation, the gas is not allowed to pressurize. Brewers use airlocks to take advantage of the positive pressure created by the CO2 production of the yeast to keep unwanted oxygen, wild yeasts, bacteria, and other invaders out of the vulnerable, fermenting wort. Getting the fizz into beer can be done in a number of ways.
For bottling, a small amount of sugar is added to the beer, sometimes with the addition of a strain of yeast specifically developed for bottling. Once the bottle is sealed, the added sugar allows the yeast to produce enough CO2 to pressurize the bottle. When the bottles are cool, more of this CO2 will chemically dissolve into the beer, escaping when the bottle is uncapped. As the liquid warms up, you can see the gas coming out of solution as it rises up from the bottom of your glass. This process is called bottle conditioning. Cask or keg conditioned ales pretty much do the same thing. All of this usually takes about two weeks, which can be a long time to wait if you’ve already spent three weeks or more waiting to taste your beer. But like a lot of things, it can be worth it.
Force carbonating is a different story. This process involves forcibly pumping CO2 into the beer without the addition of sugars. After kegging the beer, brewers add as much gas as the keg will hold and then chill the beer. Once it’s cold, brewers shake the keg to force more gas in and return it to the cooler. Within a day or two — sometimes even hours if the beer is already cold enough — the beer is carbonated and ready to drink. Macrobrewers pasteurize and filter after primary fermentation so the beer contains no yeast but is full of dissolved CO2.
That’s how beer converts from crushed grains, leaves and water to wonderful elixir; proof, according to Benjamin Franklin, that God loves us and wants us to be happy.