exBEERiment | Impact Of Storing Beer In A Glass Growler

Author: Steve Thanos

One of the many pleasures of beer is sharing it with family and friends, which for those who keg their own or like to take some home from the local pub, often requires the use of a vessel for transport. Perhaps the most popular package is the glass growler, as they’re relatively inexpensive and come in various sizes.

Despite the general impermeability of glass, the process of filling a growler not only results in exposure to oxygen, but it also forces some CO2 out of solution, leading to hastened deterioration of the beer. For these reasons, it’s often recommended to consume beer from a growler as soon as possible. However, some claim that beer in a glass growler can withstand lengthier storage periods as long as it is filled completely and remains tightly sealed until the beer is to be consumed.

In a recent xBmt performed during the Covid-19 pandemic, the brewer was unable to consistently distinguish a Brut IPA stored in a stainless CO2 pressurized growler for 3 days from one served straight from the keg, which indicated little if any oxidation or carbonation loss occurred. Having experienced issues with glass growlers before, I designed an xBmt to test out the impact storage over a few days would have on a Vienna Lager.

| PURPOSE |

To evaluate the differences between a Vienna Lager served direct from the keg and one stored in a glass growler for 4 days.

| METHODS |

Lager styles are known to be sensitive to oxidation, so I designed a simple Vienna Lager recipe for this xBmt.

Proper Nomenclature

After collecting the full volume of mash water, which was adjusted to my desired profile, I began heating it up then moved on to milling the grain.

Once the water was adequately heated, I incorporated the grains then checked to make sure it was at my target mash temperature.

The mash was left to rest for 60 minutes, during which I intermittently stirred it.

While waiting on the mash to finish up, I weighed out the kettle hop additions.

When the mash rest was complete, I removed the grains and boiled the wort for 60 minutes before chilling it with my IC.

A refractometer reading showed the wort was right at my target OG.

Next, I racked the chilled wort to a fermentation keg and place in my chamber to finish chilling to my desired fermentation temperature of 50°F/10°C, at which point I pitched a pouch of Imperial Yeast L13 Global.

After 2 weeks, I raised the temperature in the chamber to 68°F/20°C and let it sit for an additional 3 days before taking a hydrometer measurement indicating it was at my target FG. At this point, I cold crashed the beer to 32°F/0°C overnight then transferred it to a CO2 purged keg that was placed in my keezer. Following 12 hours of burst carbonation, I reduced the gas to serving pressure and let it condition for 2 weeks before filling a 64 oz/1.9 L glass growler.

The filled growler was placed in my keezer where it remained 4 days before I began my evaluation.

| RESULTS |

Due to social distancing practices as a result of the COVID-19 pandemic, data for this xBmt was unable to be collected in our typical manner. As such, temporary adaptations were made involving the author completing multiple semi-blind triangle tests in as unbiased a way as possible.

Utilizing 4 opaque cups of the same color where 2 were inconspicuously marked, one set was filled with the beer poured from a keg while the other set was filled with the beer stored in a glass growler for 4 days. For each triangle test, 3 of the 4 cups were indiscriminately selected, thus randomizing which beer was the unique sample for each trial. Following each attempt, I noted whether I was correct in identifying the unique sample. Out of the 10 semi-blind triangle tests I completed, I needed to identify the unique sample at least 7 times (p<0.05) in order to reach statistical significance. In the end, I correctly identified the unique sample just 4 times (p=0.44), indicating my inability to reliably distinguish a Vienna Lager served direct from the keg from one that was stored in a glass growler for 4 days.

Based on past experiences with glass growlers, I went into this evaluation confident I’d be able to tell these beers apart, but that was not the case at all. Both beers were equally carbonated and perceptibly identical in terms of aroma, flavor, and mouthfeel.

| DISCUSSION |

Glass growlers are popular in breweries for a number of reasons, namely their cost and general oxygen impermeability. However, it’s widely believed that the process of filling a growler from a tap exposes beer to enough oxygen to significantly reduce shelf life, hence the common recommendation to consume beer from growlers as soon as possible. My inability to reliably distinguish a Vienna Lager poured straight from the tap from one that was stored in a glass growler for 4 days indicates the storage vessel had minimal if any perceptible impact.

While certain gadgets exist that allow for purging of growlers with CO2 prior to filling, I’ve not seen one used at any of the breweries I frequent. Rather, the growler is usually fill to the brim directly from the tap and immediately capped. It’s possible this process results in the oxygen in the growler being completely displaced by the beer and CO2 expressed during filling, reducing the chances of oxidation, which might explain these results.

I was admittedly surprised with my inability to tell these beers apart. It’s true that most of the negative experiences I’ve had in the past have involved opening a growler for samples multiple times over the course of a few days, but given what we know about cold-side oxidation, I was convinced the process of filling the growler would expose the beer to enough oxygen to have a detrimental effect. The fact it didn’t in this xBmt suggests to me that glass growlers may be better for beer storage than I presumed, at least when its filled to the brim with Vienna Lager and remains sealed. I’d be curious to see how a more sensitive style like NEIPA reacts to such storage as well as the impact taking samples from a growler has on beer quality.

If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!

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