Carbonating, Conditioning, and Aging
Carbonating is the process of adding carbonation to beer. Carbonation accentuates beer flavors and aromatics, and allows the beer to “come-together”. Carbonated beer will develop a layer of foam (or head) when poured. The head will linger on the sides of the glass when consumed; this is called lacing. Well-carbonated beer will have a thick, lingering head composed of small bubbles. It will also leave good lacing, wherein you can see layers of foam develop from subsequent sips. Carbonating itself is a very straight-forward process; the following processes of condition and aging can be a bit more complicated.
Different styles of beer will call for different levels of carbonation. Carbonation is measure by a number of volumes of CO2. This can range anywhere from 1.5 volumes of CO2 on the very low end, up to 5.0 on the very high side. Most beers will fall in the 2.0 - 3.0 range. Generally, light colored and hoppy beers will be more highly carbonated, while darker, maltier beers will have lower levels of carbonation.
Brewers will usually bottle their brews using a process called bottle conditioning. Those with the inclination may find themselves kegging homebrew. The fundamentals between these two processes are the same, the means different.
Conditioning is the process wherein flavors meld together, under the influence of carbonation. This is the main differentiator between “green” (young) beer and properly aged beer. For example, IPAs may never really taste “good” until they are conditioned; going into and coming out of the fermenter, they taste overly bitter with very little hops flavor and aromas. Once carbonated and conditioned, however, hops flavors and aromatics are accentuated, bitterness seems to become toned down a bit, and the beer really comes together.
The timeframe for conditioning is not consistent between beer styles, and depends on several factors. These factors can include alcohol level, malt bill, and temperature of storage. Generally, at least 2 weeks under carbonation will properly condition most beers, though some beers may benefit from extended conditioning.
Generally, hoppy beers will take a couple weeks to condition, and should be consumed as soon as they are ready. Hops aromas and flavors fade over time, usually over a period of at least 3-4 months.
Malt- and yeast-focused beers with moderate alcohol (under 6% generally) will condition in about the same timeframe. While they are good when fresh, they may become a bit more complex over time, depending on the specific recipe.
Malt- and yeast- focused high-alcohol beers (anything over ~7%) will typically take a couple extra weeks of time to condition, and will almost always improve with age. This is especially true for imperial stouts, barleywines, and strong Belgian beers. Due to their malt make-up, they will develop deeper complexities over time, and become much better. For these beers, the issue surpasses conditioning, and is termed aging.
As a side note, hop-focus beers are any style where hops are the main theme of the beer. American pale ales, IPAs, and double IPAs are the main beers here. Malt-focused beers include most English ales, lagers, and most dark beers, such as porters and stouts. Yeast-focused beers are those with strong yeast characteristics, these mainly being Belgian beers, or most beers with Belgian yeasts.
Aging is the long-term storage of beers. The main driver of aging is a minute amount of oxygen interacting with malt and alcohol characteristics. Aging can be performed either before carbonating and conditioning (bulk-aging) or after carbonating and conditioning (bottle-aging). The beer styles that stand up best to aging are those with either strong malt characteristics, high alcohol content, lack of strong hops character, or sour/brett beers. These beers have a variety of chemicals that will change in the presence of a light amount of oxygen. Generally, aging timeframes can range from 3 months to 3 years.
Bulk aging (also called secondary aging) is done after primary fermentation. The beer is racked into a secondary vessel and sealed with an airlock. The secondary vessel (typically a carboy) is topped up into the neck to avoid excessive oxygen contact, and the beer is stored for an extended period. The beer is sampled once every so often, and when the brewer judges it to be ready, is then bottled or kegged.
Oak additions take time to leech flavors from the wood into the beer. Depending on the form of oak (chips, beans/cubes, spirals, or staves), this can mean anywhere from 2-4 weeks to 2-4 months.
Fruit additions are typically done to Belgian beers to enhance fruit complexity, but can be added to any beer style. The fruit is added in a secondary for two reasons. First, the sugars must be fermented completely, otherwise the bottle beer will run the risk of over-carbonation and possibly bottle-bombs. Second, adding fruit before or during primary fermentation will drive off most of the delicate aromatics of the fruit. Keep in mind, fruit flavor extracts do not contain fermentable sugars, thus can be added directly at bottling or kegging.
Two-stage dry-hops will mostly be done on big imperial IPAs. Here, the first stage of dry-hops is added after primary and allowed to settle out, usually 5-7 days. After, the beer is racked onto a second stage of dry-hops in a secondary vessel. The beer will again sit on the dry-hops for 5-7 days. After, the beer is then bottled or kegged.
High alcohol beers tend to taste harsh or “hot” after fermentation. These beers can be transferred to a secondary, where yeast and oxygen will help break-down and soften harsh tones. This usually takes a month or two, and often (depending on beer style) is combined with an oak addition, which helps mask lingering alcohol tones.
Finally, sour beers are very commonly secondary aged. Bacteria and brettanomyces are very slow fermenters, and these beers require a minimum of 3 months for the correct flavor profile to develop. Briefly, the microbes will eat through the by-products of fermentation and develop acids (typically lactic and acetic acids). Brettanomyces are infamous for chewing through large-charged sugars (namely dextrins) that clean yeast cannot ferment, and creating a mélange of complexities in the beer. This is a slow, very gradual process, and ample time is needed for this to complete.
As a final note, if you bulk age for a long period of time and intend on bottle-conditioning the beer, it may be a good idea to add a little extra yeast to the beer, so that there are enough cells left to ferment the priming sugar and carbonate the beer. Any yeast will work, but champagne yeast is a common choice, as it is inexpensive, well-adapted to fermenting simple sugars, and is a clean fermenter, adding no extra flavors to the beer.
Bottle aging is done after fermentation has completed. The beer is bottled and stored at cellar temperatures for a period ranging from 6 months to 6 years. The amount of time to bottle age a beer for is not specific; it depends on when the brewer feels the beer is ready. Temperature should be fairly low (mid 50s generally), and away from light.
Aging in the bottles will be much more gradual than in a secondary fermenter due to the lack of oxygen. The best beer styles for bottle aging include many of those well-suited to bulk-aging (and often, are done hand in hand). Barleywines, imperial stouts, big Belgian beers, and sours are the main aged beers, but anything with a malt or yeast focus, with a large amount of alcohol (or, in the case of sour beers, acids) will be fine for bottle aging.
The advantage of bottle aging beers is the ability to taste the beer along the way, and see how it develops. Because the beer is already carbonated and conditioned, there is no flavor guesswork, as in the case of bulk aging. Beer careful when doing this, as by the time the beer is perfect, you may not have much left!