Aging Gracefully

Will your beer grow mellow and pleasing or develop into a crusty old coot? The key is how you treat it in its youth. Learn the science of aging, and keep your beer from becoming disagreable before its time.

Although aging is normally thought of as something that happens between bottling time and drinking, each step you take in beermaking helps determine the chemical makeup of the final product and how that makeup will change over time. The amount and type of yeast you use, the quantity of oxygen you dissolve in the wort at each stage of handling, fermentation and storage temperatures, and the storage containers you choose all influence how your beer ages. An important part of evaluating your aging techniques is understanding what flavors are controlled by aging and which change little over time.

Preventive Beer Maintenance

What you do at pitching time is critical to your beer’s flavor and long-term survival. Wort aeration, pitching rate, and fermentation temperature all contribute to the character of the final product. A sweaty or even a solvent-like or banana flavor in your beer that you attribute to aging problems may in fact indicate that it’s time to reconsider your yeast choice.

Yeast are incredible little chemical processing plants. Besides churning out ethanol and carbon dioxide, yeast have a pretty busy production schedule, making all sorts of things that eventually turn into beer. For example, brewer’s yeasts produce a variety of fatty acids that can contribute “goaty,” “sweaty,” or “soapy” flavors to beer. Each yeast strain produces a quantity and proportion of these acids unique to, or characteristic of, that strain. Other acids are also produced, such as acetic and lactic acid for example.

In addition to the great variety of acids, yeast also produce a number of different alcohols. There are two convenient categories of alcohol for the amateur brewer: ethanol and everything else. The “everything else” group is more often called the fusel or “higher” alcohols. Higher-alcohol production is somewhat unique for every yeast strain and also contributes to the strain’s own special character.

Yeast enzymes encourage the chemical combination of acids and alcohols to form esters. For example, acetic acid and ethanol can combine to form ethyl acetate, the source of fruity, solvent-like flavors. Isoamyl alcohol and acetic acid can combine to form isoamyl acetate, which can give beer a banana-like flavor. Since a given yeast strain can uniquely determine which acids and alcohols are produced during fermentation (and in what quantities), it makes sense that ester production is also a characteristic of a given yeast.

Ester production increases with higher fermentation temperature, lower levels of dissolved oxygen, higher gravity wort, and lower pitching rates. If you’ve noticed fruity, solvent-like, or banana flavors in your beer, try brewing a few mid-gravity beers with original gravities around 1.050 or below, aerating well (better than you have been), and using an adequate pitching rate. A good rule of thumb for pitching is to use about 1/2 to 3/4 cup of yeast solids for a five-gallon batch, minimum.

No Beer Before Its Time

By now you’re asking, “That’s nice. What does this have to do with aging beer?” In a way, the answer is “Nothing!” Although the use and choice of yeast do have issues that are time sensitive, the three flavor-contributing families just mentioned (fatty acids, fusel alcohols, and esters) are all components that end up in the final beer and don’t change much, if at all, with time. Control of these factors has to be handled through yeast selection and control of the fermentation itself. After fermentation is over, it’s too late. If aging doesn’t help here, then what can it do for you?

Two other substances produced by normal fermentation include diacetyl and acetaldehyde. Diacetyl is described as having a “fresh butter” or butterscotch taste. Over the past several years the American Homebrewers Association style guidelines have reduced the acceptable levels of diacetyl for almost all styles, and most brewers generally consider it an undesirable flavor.

Fortunately, yeast re-absorb much of the diacetyl produced during early fermentation, given the opportunity and if they didn’t produce too much to begin with. After fermentation appears to be complete, ales should be kept at fermentation temperature for about two days for this final “diacetyl rest.” Carefully racking off the trub at the end of the primary ferment will help ensure you avoid off-flavors from degenerating yeast while still providing ample yeast for diacetyl pick-up.

Fortunately, yeast re-absorb much of the diacetyl produced during early fermentation,

Somewhat less troublesome but harder to pronounce, acetaldehyde (a-se-tal-de-hide) is also produced naturally during fermentation. The acetaldehyde level in wort increases during the process to a maximum, then decreases as it is converted to ethanol. Acetaldehyde
contributes a flavor described as “green apple” and in small amounts isn’t considered a big defect in many beers. But if it’s very apparent, tasters may say the beer needs to spend more time in the secondary or that the beer is very young. Usually, aging will continue to reduce acetaldehyde to unnoticeable levels as conversion to alcohol continues.

Airing Out the Difficulties

One by-product of yeast is hydrogen sulfide (H2S). Hydrogen sulfide produces a strong rotten-egg smell and is sometimes noticed at the beginning of fermentation. It can be carried over into the finished beer if not allowed to vent from the fermenter. The CO2 produced during fermentation will scrub hydrogen sulfide from the wort, and open fermentation or the use of an airlocked carboy will allow its escape.

Some brewers use stainless soda canisters (cornelius kegs) for secondary fermentation, and venting is important here, too. An airlock arrangement can be set up on a cornelius keg by bleeding gas from the “in” tube of the keg using a gas fitting and a connected length of tubing. The end of the tubing can be placed in a container of water for airlock security. An alternative is to simply bleed the keg twice a day as needed, using the pressure relief valve in the keg lid. Routine or continuous venting will help ensure that the finished beer doesn’t contain a sulfur-like or rotten-egg aroma.

Everything Gets Clearer with Time

American beer drinkers are accustomed to crystal clear lagers that are so light and clear you can easily read a book held on the opposite side of the glass. Our expectation of brilliantly clear beer carries over to our enjoyment of ales, also. The larger American ale brewers, such as Boston Brewing Co. (Samuel Adams) and Pete’s Brewing Co., make products that are incredibly clear as well. It’s no wonder so many people new to amateur brewing want to make their beer just as clean looking. It makes for a “professional” looking product.

Beginning brewers are sometimes disappointed with their first several batches of beer, which often lack that kind of brilliant clarity. Filtering seems like an obvious solution, but that means more equipment and more money. Fairly coarse filters, used with CO2 kegging gear, can be used to get very clear beer quickly, without having to strip out color and flavor. Fortunately, the cost, equipment, and trouble isn’t really needed. With patience and proper use of clarifying agents, very clear beer can be yours.

As the yeast in your beer finally ferment out all the sugar they can, they begin to drop to the bottom of the secondary. Some yeast strains do this quite suddenly, leaving a very clear beer after only a week or so of fermentation. You can rack to the bottling bucket and bottle, or to the keg for cool storage. If you aerated well at pitching time, there should be no need to rouse the yeast or to pitch more yeast for carbonation, or in any way disturb this clearing beer. Diacetyl reduction should also be right on target.

You can buy a variety of products to help settle out yeast, proteins, and tannins from your beer, and none is very expensive or hard to use. The most common one used in the kettle is Irish moss. Others, used only in the secondary fermenter, include isinglass, Polyclar, and gelatin. Directions are usually included with those products sold at supply shops.

Gelatin works quite well, is sold at most grocery stores, and is very inexpensive. Dissolve about 1/2 to 3/4 of a packet in one cup cool water, then bring to a boil. Pour into the carboy. This works well for those who keg — after you add the gelatin solution to the room-temperature beer, the keg can be placed in the refrigerator to cool. The yeast that was in suspension will drop out into a firm cake at the bottom of the canister, where it remains undisturbed during dispense.

Carbonation and Conditioning

There are two popular ways to get that pleasing carbonation that makes beer the delightful thirst quencher it is. By far the most popular is bottle conditioning. The idea is remarkably simple. After fermentation is complete, most of the yeast have either settled out of the beer or are well on their way. But even if the beer looks clear to the eye, there are still millions of yeast cells floating around.

To bottle condition you must give the remaining yeast just enough food (priming sugar) so they can produce the right amount of CO2 to carbonate the beer. Since the beer will be sealed in bottles when the yeast start fermenting the priming sugar, the CO2 can’t escape. It simply dissolves in the beer.

For those who keg there are two choices for conditioning the beer. One is to prime with sugar just like you would if bottling, and the other is to force carbonate. Some brewers just don’t like the idea of forced carbonation and prefer to prime, even if they keg rather than bottle. Priming sugars that are not totally fermentable can be used to add character to your beer, so even if you keg you may still want to prime a stout with molasses, for example. More often, keggers just rack the beer carefully into a sanitized soda canister and apply pressure from a CO2 tank.

A Quiet Rest in a Dark Room

The ability to keep your beer for months depends on everything you do, from putting the kettle on the boil to popping the cap off the last bottle or tapping the last pint from the keg. The beer you’ve put your heart and soul into can’t be treated like a freeze-dried camping ration just because it’s sealed in a bottle or a stainless steel canister.

Air (or really, the oxygen in it) deteriorates beer. Whenever you move beer from one container to another, be certain to avoid any sloshing, splashing, or other rough handling that causes any air to be mixed in. When oxygen from the air mixes with the beer, chemical components that would otherwise never be noticed become oxidized and produce paper, cardboard, or wood- or wine-like flavors. This oxidation process degrades a good beer very quickly. It takes only a few short weeks to go from a great beer to an undrinkable one.

High temperatures speed up the oxidation and staling process, too. Beer doesn’t like to be stored warm. The best possible storage conditions are dark, cool, and undisturbed. Ideally, store bottled or kegged ale at 50 to 55 °F (10 to 13 °C) and lager at 40 °F (4 °C), year-’round. If that just isn’t practical for you, there are several things you can do to help make the last bottle as good or better than the first. Minimize the head space when you bottle. Use oxygen-absorbing bottle caps. Adjust your batch size down so that storage times are shorter (at least in the summer).

Certain hop components, when combined with sunlight, produce a skunky aroma and flavor in beer. A skunked or lightstruck character is a serious defect that can be easily avoided by using dark brown bottles and by keeping bottled beer out of direct sunlight. Green or clear bottles provide no protection at all and aren’t recommended unless your bottles will be stored in total darkness.

As always, keep complete beer handling records including information such as dates and storage conditions. You may want to pick up a guide to beer tasting, such as Evaluating Beer (Brewers Publications) to help you identify changes in your beer over time. If you practice taking careful notes as you sample from the same batch week after week, you can begin to train yourself to detect and describe the subtle (and sometimes not-so-subtle) maturing of the beer. This can be a lot of fun, is very educational, and firmly establishes you as a true Beer Fanatic.

Issue: July 1996