Author: Jake Huolihan

The most common method used by new brewers to carbonate their beer is bottle conditioning, a simple procedure that requires little in the way of additional gear. Generally, a specific amount of sugar water is incorporated into the beer in a bottling bucket then transferred to bottles and capped. The remnant yeast in the beer metabolizes the added sugar, creating carbon dioxide (CO2), which gets dissolved into solution leading to an effervescent beer. The process takes some time, but it works, and with modern calculators, carbonation levels can be precisely tailored to one’s liking.

One posited benefit of bottle conditioning is that it can reduce the risk of oxidation since yeast consume any dissolved oxygen during the refermentation process, thus improving shelf and flavor stability. However, the common recommendation to store beer relatively warm during the conditioning period, which can be anywhere from 1 to 3 weeks, is cause for some concern since temperature is positively correlated with chemical reaction rates– any changes bound to occur will do so faster in a warm beer than in a cool beer.

With growing evidence suggesting a particular susceptibility to the deleterious effects of oxygen, packaging methods have become a major focus for brewers of hazy New England IPA (NEIPA). The internet abounds with stories of NEIPA that started out great but quickly turned, often accompanied by pictures of murky beer in shades of grey, brown, and purple. One solution to this problem involves limiting the beer’s exposure to oxygen post-fermentation by racking into a CO2 purged keg, though such a process is unavailable to those who bottle condition.

Considering the results of our recent xBmt on cold-side oxidation of NEIPA along with numerous reports of bottle conditioned NEIPA quickly discoloring, I began to wonder if bottle conditioning actually leads to a qualitative difference as compared to force carbonation. Shelving my abhorrence for the bottling process, I hunkered down to test this one out!

| PURPOSE |

To evaluate the differences between force carbonation and bottle conditioning in a New England IPA.

| METHODS |

I designed a NEIPA recipe with a fairly common grist and solid hop charges of Centennial, Cascade, and my new favorite, Loral.

Purple Haze

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 23.9 IBUs 4.7 SRM 1.062 1.016 6.1 % Actuals 1.062 1.018 5.8 % Fermentables Name Amount % Pale Ale, Finest Maris Otter (Simpsons) 6.75 lbs 45.38 Pale Malt (2 Row) US 6.75 lbs 45.38 Oats, Flaked 1.375 lbs 9.24 Hops Name Amount Time Use Form Alpha % Hallertau Magnum 14 g 30 min Boil Pellet 11.5 Cascade 21 g 5 min Boil Pellet 5.5 Centennial 21 g 5 min Boil Pellet 10 Loral 14 g 5 min Boil Pellet 10.3 Cascade 28 g 3 days Dry Hop Pellet 5.5 Centennial 28 g 3 days Dry Hop Pellet 10 Loral 28 g 3 days Dry Hop Pellet 10.3 Yeast Name Lab Attenuation Temperature Juice (A38) Imperial Yeast 74% 64°F - 74°F Notes Water Profile: Ca 174 | Mg 0 | Na 8 | SO4 150 | Cl 200 Download Download this recipe's BeerXML file

The night before brewing, after adjusting the full volume of water to my desire profile, I weighed out and milled the grains for two identical 6 gallon batches.

When I woke up the next morning, I immediately turned on the element to heat the water to slightly warmer strike temperature, at which point I transferred equal volumes to separate mash tuns for a brief preheat before mashing in to hit my target temperature.

Each mash rested for 60 minutes.

Since the variable being tested would be introduced post-boil, I collected the sweet wort from both mashes into a single kettle. The wort was then boiled for 60 minutes with hops added per the recipe.

When the 60 minute boil was complete, the wort was quickly chilled to my desired fermentation temperature of 66°F/19°C.

A hydrometer measurement showed the wort had hit my target OG.

I filled 2 identical fermentation vessels with equal amounts of wort then placed them in my temperature controlled chamber and pitched a pack of Imperial Yeast A38 Juice into each.

I checked on the beers about 10 hours later and noticed both were fermenting actively. The following day, 2 since pitching yeast, I added the biotransformation dry hop charge.

Signs of fermentation were absent 8 days post-pitch, so I took initial hydrometer measurements indicating FG had been hit; a second round of measurements 3 days later were unchanged, confirming fermentation was complete.

The time had come to begin the task of preparing to bottle 5 gallons of beer. Each beer was first transferred to a CO2 purged 5 gallon corny keg, only one of which had a pre-determined amount of sugar solution in it. The force carbonation beer was immediately placed in my keezer and hit with gas per my usual routine, while I used a Blichmann Beer Gun to fill each bottle from the other keg.

The filled and capped bottles were placed in a room that maintains a fairly consistent 66°F/19°C to carbonate. After 1 week, I impatiently chilled a bottle for an early comparison and decided to leave them be for another few days to ensure they were properly carbonated. Visual comparisons to the kegged version at both of these points were very interesting, the bottle conditioned beer appearing noticeably darker both times.

Wanting to give the bottle conditioned beers enough time in the fridge to allow things to drop out of solution, I began collecting data after another week, at which point the visual difference between the beers was even more stark.

| RESULTS |

A total of 20 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of the force carbonated beer and 2 samples of the bottle conditioned beer in different colored opaque cups then asked to identify the sample that was unique. While 11 tasters (p<0.05) would have had to identify the unique sample to reach statistical significance, only 6 (p=0.70) made the correct selection, indicating participants were unable to reliably distinguish a New England IPA that was force carbonated in a keg from one that was carbonated via bottle conditioning.

My Impressions: Sampling these beers next to each other just 10 days after they were packaged, I was pretty convinced they were different and confident tasters would be able to distinguish them. Of course, I not only knew the variable, but saw their difference in appearance, which undoubtedly biased my perception. In an attempt to reduce at least some of this bias, I attempted a total of 10 semi-blind triangle tests served to me in opaque cups, out of which I chose the unique sample a whopping 2 times. I actually did worse than chance. My first 5 trials were completed when the bottle conditioned beer had been conditioning for 10 days, while the last 5 trials were occurred when the beer had been conditioning for 21 days. The beer itself was great! I really enjoyed the aromatic punch that came from the hops used, it reminded me of grapefruit juice with a citrus bite.

| DISCUSSION |

Bottle conditioning certainly has it’s critics, not only those who loathe all that’s involved in getting 5 gallons of beer into a bunch of bottles, but some also claim it produces a different quality than force carbonation. Then again, the fact it necessarily involves a refermentation period has led many to believe bottle condition can reduce the risk of oxidation in the package, thereby improving overall shelf stability. With the results from this xBmt corroborating those from our last comparison of bottle conditioning and force carbonation, it seems a plausible assumption that both methods produce qualitatively similar characteristics.

However, accepting such a conclusion would require ignoring one glaring difference– the surprisingly disparate appearance of the beers. As far as I can tell, stories of beer turning purple and gray were all but absent until a few years ago when brewers began reporting observations of such in NEIPA, both commercial and homebrewed. Various hypotheses have been posited as to the cause of this issue, the most common culprit being post-fermentation oxidation, an issue bottle conditioning can presumably help to ameliorate. If this is true, why did the bottle conditioned beer change color?

Even more confounding is that, despite this very obvious color change, tasters blind to the appearance of the beers could not reliably tell them apart based on aroma, flavor, and mouthfeel. The murky, purple, disgusting looking bottle conditioned sample tasted the same as the creamy, orange, beautiful force carbonated sample to a majority of participants.

What?!

I’m not even going to attempt to provide a cohesive explanation as to what’s going on, so instead I’ll free associate…

Maybe there’s a point of no return with NEIPA… the one in the cold-side oxidation xBmt was pushed into a purged keg with CO2… I purged the keg for the force carbonated beer in this xBmt but transferred it via gravity… perhaps the presumably small amount of oxygen exposure from the exchange of air is enough to begin the staling process such that, even though they looked different, they had the same aroma and flavor because they were equally oxidized at the time of packaging.

Out of curiosity, I did a little side experiment to test the impact oxygen exposure in a warm environment has on NEIPA, similar to what was done in the recent xBmt comparing flaked oats to wheat malt. I left uncovered samples of both the force carbonated and bottle conditioned beers on my counter for 3 days, taking a photo daily to document any changes in appearance.

Immediately after pouring

After 8 hours

After 16 hours

After 36 hours

After 48 hours

The results were astonishing. I’ve left half-full glasses of other styles of beer out in similar situations numerous times, usually unintentionally, and never have I witnessed such a rapid change in appearance. While bottle conditioning, for whatever reason, does seem to hasten the onset of the discoloration compared to kegging, the fact both samples so quickly turned suggests the issue has more to do with the style overall.

I have no plans to go back to bottle conditioning my beers, I far prefer the ease of kegging, and unsurprisingly, the dark NIEPA from the bottle was very unappetizing to me. In fact, prior to my 10 triangle test attempts, I’d convinced myself I’d not only be able to tell the beers apart, but that the force carbonated version was much better. How easily our perception can be influenced by the way something looks. All in all, I find it sort of comforting that tasters could not tell the beers apart when appearance was hidden, as it suggests decent tasting examples of NEIPA can be made by those who don’t keg, even if it ends up resembling something from another planet.

If you have any thoughts about this xBmt, please share them in the comments section below!

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