exBEERiment | Impact Including Roasted Grains In The Decoction Has On A Czech Dark Lager

Author: Jordan Folks

When most people think of dark beer, it’s likely styles like Porter and Stout come to mind, both of which are known for their assertive roast flavors. Dark lagers, on the other hand, are typically supposed to present with a more delicate and smooth roast character that’s free from any acridity. For lagers that are traditionally decocted, like Czech Dark Lager, it’s often recommended to withhold the roasted grains until any decoction steps are complete.

In addition to the fact roasted grains have already had their starches broken down and hence don’t require mashing, the boiling that occurs during a decoction can extract tannins, leading to astringency in the finished beer, while also increasing the chances of burnt flavors. It’s said that adding these grains post-decoction avoids these characteristics while imparting a similar color and desirable roast profile.

While decoction seems to have fallen out of favor among many brewers, I continue to employ this traditional method when making certain lager styles. As it pertains to Czech Dark Lager, I’ve always withheld the roasted grains until after the decoction. However, I was curious about claims that decocting roasted grains leads to harsh roast character, so I designed an xBmt to test it out for myself.

| PURPOSE |

To evaluate the differences between a Czech Dark Lager where the roasted grains withheld until after the decoction step was complete and one where the roasted grains were included during the decoction step.

| METHODS |

For this xBmt, I designed a simple Czech Dark Lager recipe that I felt would allow any differences to shine through. Big thanks to F.H. Steinbart for hooking me up with the malt for this batch!

Burn The Witch

After collecting the full volume of water for two 5 gallon/19 liter batches, adjusting each to the same mineral profile, and getting them heating up, I milled the grain, making sure to withhold the roasted grains from both.

With each batch of water properly heated, I incorporated the grains and set the controllers to maintain the same 144°F/62°C initial mash temperature.

During the mash rests, I weighed out the kettle hop additions.

After the 60 minute saccharification rests, I pulled 1/3 of the mash from each batch for the decoction step, adding the roasted grains to one while the other was left alone.

When the 10 minute decoctions were complete, I returned them to their respective main mashes then added the roasted grains to the other batch.

The mashes were held at 160°F/71°C for 10 minutes, after which the grains were removed and the worts were boiled for 60 minutes before being chilled with my JaDeD Brewing SS Coil Hydra IC. Refractometer readings showed a slight difference in OG.

After transferring the same volume of wort from either batch to sanitized fermentation kegs, I pitched identical amounts of Imperial Yeast L29 Lookr slurry into each one.

Following a week of fermenting at 50°F/10°, I gradually raised the temperature of the beers to 62°F/17°C for a 2 day diacetyl rest. Hydrometer measurements showed the beers were at the same FG.

Next, I reduced the temperature to 31°F/0.5°C then pressure transferred the beers to CO2 purged serving kegs that were placed on gas in my keezer. After 4 weeks of lagering, they were carbonated, clear, and ready for evaluation.

| RESULTS |

A total of 18 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of beer where roasted grains were added after the decoction and 2 samples of the beer where roasted grains were included in the decoction in different colored opaque cups then asked to identify the unique sample. In order to reach statistical significance, 10 tasters (p<0.05) would have had to accurately identify the unique sample, thought ultimately only 4 did (p=0.90), indicating participants in this xBmt were unable to reliably distinguish a Czech Dark where the roasted grains were added post-decoction from one where the roasted grains were included in the decoction.

My Impressions: Out of the 5 semi-blind triangle tests I attempted, I correctly identified the odd-beer-out just twice, indicating my general inability to tell these beers apart. While I thought I perceived the beer where the roasted grains were included in the decoction as being a bit harsher prior to lagering, once both beers were ready, any perceptible differences had vanished, and neither possessed any acrid flavors.

| DISCUSSION |

One of the more common concerns when it comes to dark lagers is ensuring they possess the desirable roast flavors without tasting acrid, ashy, or burnt. Most brewers accept that these unwanted characteristics are largely a function of heat, hence the recommendation to withhold roasted grains until after any decoction steps are complete, which typically involves adding them toward the end of mash step. Interestingly, tasters in this xBmt were unable to reliably distinguish a Czech Dark where the roasted grains were added post-decoction from one where the roasted grains were included in the decoction.

The fear of acridity from boiling roasted grains stems from the idea that doing so causes pyrolysis; however, the temperature at which this process occurs is north of 550°F/300°C, far above the boiling point of water and wort. It should also be noted that darker mashes have a fairly high buffering capacity that helps keep the mash pH from getting into the range where tannin extraction occurs. It’s also possible the use of dehusked Carafa Special helps explain why the beers were as similar as they were.

I enjoy employing traditional brewing processes, in part because it’s just fun, but I also tend to believe it contributes something positive to my beers. The idea that boiling roasted grains during a decoction would lead to a harsher roast character was one that made sense to me, and hence the fact neither tasters nor I could distinguish these beers was a bit of a surprise. While I’m not ready to abandon the practice of withholding roasted grains from decoctions, this experience has left me feeling at least somewhat less concerned should I forget to do so in the future.

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

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