Exploding Growlers

by Chris Lasord Jr.

As a neophyte beer drinker in the late 1950s I loved to bring draft beer home from
the pub.   The only way to do it was in waxed cardboard containers which would
easily pass as take-out Chinese soup containers if some authority figure ever
stopped to ask what you were carrying.  The downside was the cardboard eventually
go soggy and leaked.  That took several hours and if you still had any beer left by
then, well, I guess you deserved it.

In the 1980s, as craft beer emerged more and more people wanted a better way to
bring this amazing beverage home, fresh, direct from the tap.  Enter the growler.
A growler is simply a glass jug that carries a half-gallon of beer. Some are plain and
simple while orders ornate.  Some can hold upwards of two liters with a clampdown
ceramic top and a metal handle/grips.  Some even have neat cooling packs complete
with carrying straps.  And some explode.

Home brewers have long recognized that glass growlers are not really suited for use
in carbonation since they cannot hold the pressure.  Growlers are designed to
transport beer and that's it.  Now however some breweries and pubs are getting
customer complains of exploding growlers.  So here are some things to consider the
next time you take home a growler and hope to avoid the worst.

All beer is best if it's kept cold from the brewery to the distributor to you.  That's
especially true for craft beers which are often unfiltered and unpasteurized.  In many
cases that means there is at least a small amount of yeast in the beer.  Depending
on the style there just might even be more than a small amount.  That should never
be a problem in your growler however as it gets bounced around in your car or as
you move it around, on occasion,  the yeast starts getting kicked up into the beer
and can easily start fermenting again.  That is especially true if the growler is in a
warm environment. Cold environments cause yeast to go dormant, but once it’s warm
it can get back into solution, start eating a little bit more sugar and release more
CO2, creating more pressure inside the growler.  It's that pressure that can lead to
an unexpected and most definitely unwanted explosion.

So, temperature is the key, but just what temperature? You'll likely be surprised to
know that many strains of yeast get happy around 62F – 65F and some can even be
active in the 50F range.  So what may seem like a fairly chilly environment to you  is
a vacation in Bermuda to yeast.

In general growlers are simply re-used containers and that's another problem. They
are glass and as such are not flawless. You growler may have been bought as brand
new but when you return to the brewery/brewpub with it  things have changed.  And
indeed, that's true sometimes for new growlers.  Think about it.  That both new and
old growlers have been stored, rinsed, cleaned, and (re)filled.  In that process, plus
it's transportation and general moving around your house and the brewery/bar the
growler gets banged around a lot.  They bump and knock against wall, tables, and
even other growlers.  They're stored on shelves and racks, bunched and bruised
with other items. All this can create tiny microfractures in the glass that,under normal
pressures wouldn't mean a thing.  You could safely use it many, many times.  
However, under an elevated pressure those microfractures could easily crack and
split. You should always look for chips, cracks, and bubbles in the glass.  Any of
those means your growler is potentially unsafe.  At that point it's wise to just throw it
away and get a new one.   

There is a simple rule to avoid explosions even in a flawed container and that is to be
sure that the  beer/growler is refrigerated at all times.  While that is simple for the
consumer to do there times beyond his control when that is not the case. The growler
was likely stored warm in the warehouse and then were delivered to stores where
they were also kept warm, which created – for a limited number of pre-filled growlers
– a very dangerous situation.  

Growlers are big business today.  So much so that onee of the hottest new beer
related concept is a "growler filling station". The premise is simple: beer to go. The
place has a number of rotating taps of craft beer you fill your growler with. It’s not a
brewery, it’s not a bar (although most of them will allow you to drink beer on premise,
which blurs the lines).  Many of these places prominently feature signs advising that
the filled growler be kept cold at all times.

It's good advice

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Growler Safety