We get asked this question all the time.
The shelf life of a filled growler depends on a lot of factors that could potentially spoil the beer. All of these factors are the same that we battle in the brewery to make sure the beer gets into the container and out to the customer in the best condition possible.
In short, it could last less than a day, or maybe a month or so. Here are some factors that contribute to the shelf life of a growler fill:
The cleanliness and how sanitary the growler is
Even one bacteria or wild yeast cell that’s present will over time multiply into billions and produce off flavours, and sometimes more carbonation.
Whether the growler has air in it when it is filled
Having air come in contact with the beer will spoil the hop flavour and aroma very quickly and change the malt flavours. It will also provide more oxygen to any leftover yeast when it should be in a dormant state. Other bacteria and wild yeast will also use this oxygen and will speed up their multiplication.
The type of growler that the beer is in and the quality of the seal of the lid
If the growler is glass, UV light will get into the beer and slowly spoil it. The darker the glass the better; better yet - use a stainless growler. If the seal on the growler is poor then CO2 will escape and the beer will lose carbonation. If something can escape then there’s also the risk that air and foreign bacteria and yeast can get in (which of course is a bad thing).
How the Growler is stored once is has been filled
If a filled growler sat out in the sun on a hot day then the beer inside won’t last the day. The heat will promote any yeast or bacteria to grow like crazy, and it will also most likely kill the delicate brewing yeast and both of these will produce any number of off flavours. The UV light will ruin the hops and malt and create a cheesy or skunky flavor and aroma along with a sweet and unpleasant malt flavour. The pressure inside will build up in the heat and CO2 will escape and other things can get back in. And lastly, if the growler has been opened then air has been let in and CO2 has been let out and the beer is not going to last beyond that day (sometimes not even that). Store it in a dark and consistently cold place and when you decide to drink it, drink it all! And then, clean the growler(!!).
Old Yale Brewing has a very advanced growler filling station
We rinse all the growlers before filling although the state of the growler is mostly out of our control and there is no way of properly sanitising them on demand, so this is the most common point of spoiling for the beer inside the growler. We then purge all of the air out of the growler with CO2. The beer is filled in to the growler right from a stem at the very bottom and it is fobbed (foam coming out of the top) when the cap is placed down. This ensures the maximum amount of air is pushed from the growler. If everything goes well and it is stored carefully then the beer could last a long time, maybe up to a month or so.
We hope this blog was helpful, and will extend the life of all your future growler fills.