Author: Jake Huolihan

The German Beer Purity Law known as the Reinheitsgebot mandated that beers be produced with only 4 ingredients, none of which were carbon dioxide from an external source, often used by modern brewers for carbonation purposes. Despite these limitations, German brewers developed a few methods for carbonating that adhere to the purity law including kräusening, recapture of CO2 produced during fermentation, and spunding, which is perhaps the easiest of them all. (bunging) the fermentation to allow for the co2 produced during carbonation to naturally carbonate the beer.

Spund translates to bung, hence spunding involves bunging the fermentor before fermentation is complete, disallowing the escape of CO2, which ultimately carbonates the beer. Even with our ample access to packaged CO2 and no laws restricting its use, many modern brewers have adopted this method, as it allows them to save money by reusing what would otherwise be lost. Additionally, some contend it has a qualitatively positive impact on beer by producing a finer carbonation and preserving certain characteristics believed to be lost when force carbonating.

There are some things that require consideration when it comes to spunding. Brewers must know what their FG is going to be, which requires a good enough brewing process to be able to predict, and they need to be attentive to fermentation in order to spund at the appropriate time. The only piece of gear required is a spunding valve, which is basically a pressure relief valve that holds a set amount of pressure in the keg.

As a lover of German beers, I was interested to see if spunding, a method I’ve used a handful of times, results in a beer that’s noticeably different than a force carbonated beer.

| PURPOSE |

To evaluate the differences between a pale lager carbonated using force carbonation and one carbonated with the spunding method.

| METHODS |

I went with a simple German Helles Exportbier in hopes it would allow any differences to shine through.

Bubbles

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 6 gal 60 min 26.5 IBUs 4.0 SRM 1.053 1.016 4.9 % Actuals 1.053 1.015 5.0 % Fermentables Name Amount % Pale Malt (2 Row) US 5.5 lbs 45.36 Weyermann Pilsner Malt 4.5 lbs 37.11 Weyermann Vienna 1.25 lbs 10.31 Carafoam (Weyermann) 8 oz 4.12 Carahell 6 oz 3.09 Hops Name Amount Time Use Form Alpha % Hallertau Magnum 19 g 60 min Boil Pellet 11.5 Saaz 15 g 30 min Boil Pellet 1.4 Yeast Name Lab Attenuation Temperature Harvest (L17) Imperial Yeast 72% 50°F - 60°F Notes Water Profile: Ca 81 | Mg 2 | Na 46 | SO4 74 | Cl 81 Download Download this recipe's BeerXML file

I started off by reviewing Kai Troester’s BrauKaiser website where I learned wort produces 2 volumes of CO2 for every °P. Since the beer I planned to brew would be fermented at 50°F/10°C, it would retain 1.15 volumes of CO2, meaning natural carbonation would need to contribute 1.25 volumes to reach my desired serving carbonation of 2.4 volumes. Using the BrauKaiser calculator, I determined I would need to keg the beer when it was about 0.63 °P from FG. Since I’d be using a spunding valve, I figured kegging with 1 °P left to go would provide a little insurance.

I whipped up a large starter of Imperial Yeast L17 Harvest to split between the batches a couple days ahead of time.

Having prepared the night before, my brew day started with turning on my electric elements to heat the water, during which I milled the grain.

Since this variable would be introduced post-boil, I mashed in on the single 10 gallon batch and hit my target temperature.

A check of my mash pH about 15 minutes in showed it was right where I planned.

When the mash was complete, I raised the grain bag out of the kettle and let it drip into the wort that was being heated.

The wort was boiled for 60 minutes with hops added as noted in the recipe.

With the boil complete, I quickly chilled it with an immersion chiller to a few degrees warmer than my groundwater temperature.

I took a hydrometer reading to confirm I’d hit my target OG.

I proceeded to rack equal amounts of wort to separate Brew Buckets that were placed in my chamber to finishing chilling. I then collected some of the remnant wort and threw in a bit of yeast for a forced fermentation test to determine my final gravity.

The following day, with both worts stabilized at 48°F/10°C, I evenly split the decanted starter between the batches before hitting each with 90 seconds of pure oxygen.

By the next morning, the beers were happily bubbling away. It was at this point I noticed the forced fermentation beer seemed done, so I took a hydrometer measurement and found it was at 1.015 FG. This meant I would need to spund around 1.019 SG.

A hydrometer measurement take 3 days post-pitch showed the beer was at 1.020 SG, close enough for me, so I racked it to a keg.

Once the keg was full of the fermenting beer, I attached a spunding valve initially set to 15 psi then placed it next to the other beer before raising the temperature of the chamber to 60°F/16°C; when the beers reached this warmer temperature, I set the gauge to 22 psi (based on this chart).

Hydrometer measurements taken a few days later showed both beers had reached the same FG.

At this point, I kegged the force carbonation beer then moved both to my cool keezer. Since these were traditional lager beers, I went with Greg Noonan’s advice and allowed them to lager for 9 days per °Plato, which amounted to 60 days before serving them to tasters.

| RESULTS |

A total of 22 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the force carbonated beer and 1 sample of the spunded beer in different colored opaque cups then asked to identify the unique sample. At this sample size, 12 tasters (p<0.05) would have had to identify the unique sample in order to reach statistical significance, which is precisely the number who did (p=0.03), indicating participants in this xBmt were able to reliably distinguish a beer that was force carbonated from one carbonated via spunding.

The 12 participants who made the accurate selection on the triangle test were instructed to complete a brief preference survey comparing only the 2 beers that were different. A total of 5 reported preferring the force carbonated beer, 2 liked the spunded beer more, 3 reported having no preference despite noticing a difference, and 2 reported perceiving no difference.

My Impressions: I made my first few triangle test attempts right after kegging the beers, and they were mostly guesses. However, after the lagering period, I was more able to tell a difference and my triangle test performance drastically improved, I could consistently distinguish the odd-beer-out. I perceived the force carbonated beer as having a sort of honey-like aroma, quite similar to my perception of many commercially available German lagers found on US shelves, while this was less present in the spunded beer. There’s no way I could choose either of these as a favorite because I thought both were great, despite being a little different from each other.

| DISCUSSION |

Spunding is a method lauded for both its pragmatic benefits, such as using CO2 produced during fermentation for natural carbonation, as well as the impact it has on the ultimate character of beer. The results from this xBmt showing participants were able to reliably distinguish the force carbonated Helles Export from one that was spunded do support the notion that either approach has a unique impact.

Perhaps the simplest explanation for this difference is that natural carbonation imparts a different character than force carbonation, though it seems unlikely given both rely on the same CO2 gas and principle of dissolving under pressure. It could also be that spunded beer has a lower risk of oxidation since it’s kegged during active fermentation, giving the yeast time to scrub any oxygen introduced during the transfer. On the other hand, the more common approach uses these days involves packaging beer that is done fermenting, which is a major vector for oxygen ingress, then hitting it with gas to carbonate.

The preference data showing most people liked the force carbonated beer more than the spunded beer suggests either neither beer was oxidized or that people enjoy the flavors of oxidized beer. I’ve tasted many oxidized beers and while the honey character I perceived in the force carbonated beer is something some associate with oxidation, the fact is it was still very good, even 2 months after packaging.

Spunding does involve a bit more work than force carbonation, which may be unappealing to some, though I see it as a useful option in certain situations. I won’t be be adopting this method for every batch I make, but certainly for beers I plan to age for awhile, especially lagers, mostly because it’s easy insurance.

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

Support Brülosophy In Style!

All designs are available in various colors and sizes on Amazon!

Follow Brülosophy on:

If you enjoy this stuff and feel compelled to support Brulosophy.com, please check out the Support page for details on how you can very easily do so. Thanks!

Advertisements

Share this: Facebook

Twitter

Pinterest

Tumblr

Email



Like this: Like Loading...