How long will my beer stay fresh in a keg?

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?

David MacDonald
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.