Author: Ray Found

Before our species learned to wrangle gases into pressurized tanks and regulate their release with fancy gauged instruments, beer developed its fizz naturally. In the beginning, beer was often pulled directly from the vessel it was fermented in, which was commonly open and thus produced a product with carbonation levels far lower than what we’re accustomed to today. With advancements in knowledge, technology, and experience, brewers learned they could achieve a higher degree of sparkle by sealing the the still fermenting beer in a vessel, sometimes adding a small charge of sugar and/or some kräusen from a currently fermenting batch. This process came to be referred to as “conditioning.”

Still practiced by many these days, naturally carbonating beer has lost major ground due to a relatively new method that’s quicker and arguably more controlled in which pressurized CO2 is forced into the well contained beer. A web search for “history of beer carbonation” was largely futile, though it did yield one interesting tidbit from a 1903 book, One Hundred Years Of Brewing, in which the author claims that “practical and successful” force carbonation results weren’t obtained until the end of the 19th century and that it took some time to catch on, eventually making its way to larger macro breweries in the United States. Sure to please any handlebar sportin’ hipster, an early adopter and advocate of force carbonation was none other than the Pabst Brewing Company.

I made the move from bottling with natural conditioning to kegging with force carbonation a few years ago and couldn’t be happier. I love how my beer is ready to drink just a couple days after packaging rather than requiring the 2-3 weeks it takes to naturally carbonate in bottles. Further still, my love affair with IPA really began when I started kegging, as doing so allows me to drink the beer its at its peak freshness with hop aromas bursting from the glass in a way I never experienced in bottle conditioned versions. While it’s possible this difference is a function of container dimensions, my hunch is that it has more to do with the difference in storage conditions, namely temperature, and consequent yeast activity.

Recently, I’ve heard of brewers choosing to naturally carbonate their beer not in bottles, but in the keg the beer will be served from. Proponents of this so-called “keg conditioning” method have claimed it benefits the beer, even hoppy styles, by scavenging oxygen and producing a perceptibly different type of carbonation. I was curious how this tradition-harking method compared to a more standard force carbonation approach and put it to the test!

| PURPOSE |

To evaluate the differences between force carbonation and natural carbonation in the keg in beers of the same recipe.

| METHODS |

Since IPA was the first beer I made where the benefits of kegging really seemed apparent to me, I figured it’d be the perfect style for this xBmt– MACC IPA it would be!

As usual, I began my brew day a couple days beforehand by turning my high mineral city water into blank-slate RO brewing liquor.

When brew day arrived, I lit the flame under my strike water then turned my attention to weighing out and milling the grains for this batch.

Once my strike water was at the proper temperature, I added the amount of minerals and acid need to get to my target profile before mashing in to hit my desired temperature.

After a 60 minute rest, I performed my normal batch sparge procedure and collected two runnings of sweet wort in plastic buckets.

I transferred the wort to my kettle and swiftly brought it to a rolling boil.

An hour and a few hop additions later, the boil was finished. I proceeded to quickly chill the wort as low as my warm groundwater would take it, which was 82°F/28°C.

A hydrometer reading at this point revealed the crystal clear wort was at and OG of 1.070.

I pitched the yeast once it dropped to my target fermentation temperature of 66°F/19°C in my cool chamber. Since nothing was different between the batches at this point, it was no surprise they fermented similarly.

Fermentation was complete a couple weeks later at which point I confirmed both batches had attenuated to the same FG.

I dropped the chamber temperature to near freezing for a two day cold crash. This is the point where I would normally fine with gelatin, and despite many reports of it having no impact on natural carbonation, I opted not to do it for this xBmt.

One batch received the normal treatment of being placed in my keezer under 40 psi of pressure immediately after being racked to a keg. The natural carbonation batch, on the other hand, required a bit more work. I started by using my favorite priming sugar calculator to determine the proper amount of sugar needed to carbonate the entire batch to my desired level. In researching the best approach to naturally carbonating an entire batch in the keg, I found some recommendations to use slightly less sugar than I would if I were bottle conditioning; however, I chose to use the amount the calculator suggested since it seemed that was the more common method. To carbonate 4.5 gallons of beer to 2.7 volumes, the calculator suggested I use 119 grams of table sugar based on a post-fermentation temperature of 72°F/22°C. Preparing the priming sugar solution took me back to my bottling days.

I dissolved the sugar in a couple cups of boiling water then dumped the resultant solution in the bottom of a sanitized keg and racked the beer on top, the same way I used to do in my bottling days. Finally, I hit it with just enough CO2 to seat the lid and stuck the keg in a closet that maintained a fairly consistent temperature of 75°F/24°C.

Two weeks later, after confirming the keg conditioned beer was indeed carbonated, I put it in my keezer with the CO2 set my preferred serving pressure of 12 psi. Due to work travel, the beers remained untouched for 10 days before I began sampling them, and even after all that time, the force carbonated beer was notably more clear than its naturally carbonated counterpart.

| RESULTS |

A total of 15 people of varying experience level participated in this xBmt, all blind to the variable under investigation. Each taster was served 1 sample of the force carbonated beer and 2 samples of the keg conditioned beer in different colored opaque cups then asked to select the unique sample. In order to reach statistical significance with this number of participants, 9 (p<0.05) would have had to accurately identify the odd-beer-out, while only 6 (p=0.38) were able to do so, suggesting tasters were unable to reliably distinguish a force carbonated IPA from a naturally carbonated version of the same beer.

My Impressions: Other than failing one “blind” triangle test after a night of drinking, I was able to select the unique sample in every other attempt. I know it goes against the results, and this could certainly be bias speaking, but I thought the naturally carbonated beer was quite a bit different than the force carbonated sample, and not in a good way. It had what I can only describe as a sweet bitterness that I often notice in presumably old or poorly stored commercial IPA. It wasn’t actually sweet, more of a sticky sort of caramel with a harsh bitter component, while the force carbonated version tasted like MACC IPA.

| DISCUSSION |

There aren’t many xBmts I’ve approached with a strong expectation one way or the other, but I’ll admit, particularly given my personal experience with these beers, I fully expected tasters would easily be able to tell the keg conditioned beer apart from the force carbonated beer. For the first time, I’m genuinely left wondering how the hell this happened, poking around for all the potential reasons people couldn’t reliably distinguish these beers that I perceived as being so different. And it’s not like the number of tasters who were correct on the triangle test was all that close to the significance threshold, not even half got it right. The fact these results might be used by some as evidence to confirm that natural carbonation produces a beer no different than force carbonation concerns me a bit. It’s true I have a strong preference for force carbonation that’s potentially biasing my perspective, and as hard as it is for me to accept these beers weren’t qualitatively different, the evidence seems to suggest they were more similar than I perceived. It’s in times like these I’m reminded of the importance of replication.

As someone who appreciates clarity as well as being able to drink my beer as soon after packaging as possible, especially IPA and other hoppy styles, I’ll certainly be sticking with force carbonating. The good thing is both methods work! Whether through natural or forced methods, beer can be made bubbly, and ultimately each brewer is left to use whatever works best for them.

If you’ve ever naturally carbonated beer in a keg or have other carbonation experiences, please share your thoughts in the comments section below!

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