Dear Mr. Wizard:
I am thinking of kicking the bottle habit and kegging my beer instead. My biggest concern is storage temperature and how long my beer will stay good in a keg. I've seen some articles that say the beer will only stay "fresh" for 45 days. Depending upon my brewing and travel schedules, I've had some beers in bottles more than 45 days and they stayed good. Do I have to dedicate a refrigerator to maintaining a constant beer temperature and drink it all in less than 45 days?
White Lake, Michigan
Mr. WIzard replies:
The topic of beer shelf-life and freshness after packaging does not have any hard and fast rules because beers differ in their ability to stay "fresh" after packaging. In general, beer flavor changes much more slowly over time when stored cold. "Freshness" is affected by numerous variables, but the key factors for unfiltered beers are microbiological contamination, oxidation and yeast autolysis.
Microbiological spoilage is a concern of all brewers regardless of size. Off-flavors associated with wild yeast and wort bacteria manifest themselves very rapidly and are usually detectable within a week after wort production. These beers are frequently surrendered to the porcelain god and never make it to the bottle or keg stage of their lives. Other contaminants, such as lactic acid bacteria (Lactobacillus and Pediococcus species), grow much slower and can take weeks or months to rear their ugly heads. When they have grown enough to be detected, the contaminated beer may taste sour and have a very noticeable diacetyl aroma. Clean yeast, short fermentation lag times and excellent sanitation practices greatly reduce the risk of having beer contaminated with these sorts of organisms.
Many commercial breweries add an additional level of security and either sterile-filter their beer to remove bacteria that may be present or pasteurize the beer prior to or after packaging to kill any bugs that may be lurking around. Pasteurizing in the bottle or can is the most effective method of protecting beer from microbiological spoilage and about 85% of the bottled or canned beer volume sold in the United States is pasteurized in the package. Some brewers pasteurize the beer prior to packaging, using similar technology to a milk pasteurizer, but the beer can be re-contaminated during packaging (like sterile filtered beer), making this technology more challenging to use. Homebrewers and most craft brewers do not use pasteurization or sterile filtration because these methods can be expensive and can alter beer flavor when used improperly.
While microbiological contaminants radically alter beer flavor, oxidation makes beer taste stale or old. Oxidation causes beer to lose that "brewery-fresh" flavor that is the hallmark of all exceptional beers. Oxidation has been the focus of brewery research for decades and is a very well-understood topic. Brewers today address oxidation beginning at the milling stage and stay focused on the issue during all stages of beer production. However, there is no step of the brewing process more sensitive to oxidation than packaging because beer is transferred into a bottle or keg full of air (modern commercial fillers address this problem, but homebrewers have few options).
Any foaming or splashing during filling causes air pick-up and the headspace of gas in the package is another source of air. This headspace does not get displaced by carbon dioxide and is much different than the headspace of a secondary fermenter in this respect. Instead, the oxygen slowly works its way into the beer, reacts with assorted compounds and causes oxidation. Certain metal ions, like iron and copper, can do the same thing. This explains why stainless steel is the metal of choice.
Finally there is yeast autolysis. Bottle-conditioned beers certainly have their benefits. Yeast are able to absorb some oxygen and help to reduce oxygen levels. Bottle-conditioned beers typically have a creamy, tight foam and the method is traditional with its own special feel However, yeast will autolyze in the bottle given sufficient time and the result is a distinctive flavor. If the yeast load is low in the bottle, the flavor can be very appealing, as is the case with champagne, but if there is too much yeast in the bottle the beer will begin to develop the aroma of decaying yeast. Yeast autolysis also might smell like soy sauce or Vegemite.
I'll avoid your question a little bit longer, if you don't mind! Big brewers have a pretty good idea how long their beer will stay fresh because they can control how their beer is handled in distribution and have a lot of history tracking shelf-life. Anheuser-Busch (AB), Miller and Coors give their beers between 110 and 140 days on the market before they are supposed to be taken from the shelves - yes, old beer is supposed to be pulled from the shelves and returned to the brewery, where it is destroyed. I believe AB has been pretty clever with their "born-on" date because they are calling the bluff of small brewers who tout fresh beer as the best beer. Sadly, many microbrewed beers are far from fresh when purchased and AB has lured some brewers who cannot properly control their beer in the market into putting a freshness date on their bottle. Most small brewers opt for a longer "best-before" period because they lack the turnover of the major players and don't want their beers to seem old based upon a date stamp. To make matters worse, the big guys usually have better bottle fillers than the little guys and pasteurize their beer. In other words, they are beating many small brewers at the "brewed local, fresh beer" game that the little guys invented.
You are in a much stronger position to monitor freshness than commercial brewers are because you have absolute control over the beer. Use clean yeast, keep the brewery clean, minimize air pick-up during bottling and you will be well on your way to producing a beer that will stay fresh for at least 60 days after packaging. Store it hot and this period will be reduced, store it cold and it will become longer. In my experience, refrigerated homebrew can taste excellent 4 months after packaging. The thing to do is to taste your beer and develop your own theory on the subject. You can then improve shelf-life by simply focusing on those techniques in your process that can use improvement.