Author: Jake Huolihan

Of the many esoteric brewing practices, one of the least approachable to homebrewers is top cropping, which involves skimming kräusen from the top of the fermenting beer. Primarily practiced by some traditional German and English breweries, the main reason for top cropping is to harvest fresh, viable, and vital yeast for reuse in subsequent batches. However, another benefit proposed by some has to do with the actual removal of the kräusen from the beer, as some claim it can impart harsh or astringent flavors to the finished beer.

In addition to healthy yeast cells, kräusen also contains some dead cells along with excess wort proteins, hop derived compounds, and other fermentation byproducts. As anyone who has ever been curious enough to taste kräusen knows, it’s rather unpleasant stuff, very bitter, nothing like the beer that rests beneath it. As such, it makes practical sense that removing it might reduce the chances of those flavors carrying over into the finished product.

Outside of a select few modern commercial breweries, top cropping appears to be a fairly unpopular practice, and it seems even less favorable among homebrewers. Not only does the method necessitate a fermentation vessel that allows ample access to the beer it contains, but the level of attention and involvement required by the brewer is pretty high, which may be unappealing to some. But for those committed to making the best beer possible, kräusen removal may very well play a contributing factor. Possessing both a love for German lager and just enough masochism, I decided to put it to the test!

| PURPOSE |

To evaluate the differences between a beer that had the kräusen regularly skimmed during fermentation and one that was fermented with the kräusen intact.

| METHODS |

I designed a simple Helles for this xBmt, as I thought it would make an excellent tableau to explore this potentially subtle flavor altering practice.

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Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 43.9 IBUs 4.5 SRM 1.051 1.015 4.8 % Actuals 1.051 1.011 5.3 % Fermentables Name Amount % Odyssey Pilsner 11.5 lbs 96.84 Carahell (Weyermann) 4 oz 2.11 Melanoidin (Weyermann) 2 oz 1.05 Hops Name Amount Time Use Form Alpha % Loral 23 g 60 min Boil Pellet 10.3 Loral 15 g 30 min Boil Pellet 10.3 Yeast Name Lab Attenuation Temperature Harvest (L17) Imperial Yeast 72% 50°F - 60°F Notes Water Profile: Ca 49 | Mg 0 | Na 8 | SO4 38 | Cl 61 Download Download this recipe's BeerXML file

After collecting my grains the night before brewing, I prepared the water by adjusting it to my desired profile then scheduled my heat stick to turn on a few hours before I planned to start the next day. I started off the following morning by milling the grain.

With the water properly heated, I incorporated the grist then checked to make sure it was at my target mash temperature.

The mash was left to rest for 60 minutes during which I stirred every 15 minutes with my large whisk .

With the mash rest complete, I transferred the sweet wort from the MLT to the kettle.

The wort was then boiled for 60 minutes, during which the hops were added at the times stated in the recipe.

Once the boil was complete, I quickly chilled the wort.

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

Equal amounts of wort were then transferred to a pair of identical fermentation vessels that got connected to my glycol rig set to 52°F/11°C. The worts were chilled after just a few minutes, so I direct pitch a pouch of Imperial Yeast L17 Harvest into each batch.

With the beers bubbling away the next morning, I removed both lids to keep things as equal as possible then skimmed the kräusen of one of them, a process I repeated every 12 hours over 3 days.

By the final skimming, the differences in kräusen appearance were easily observed.

I stopped skimming the kräusen when I noticed fermentation dying down in order to reduce the risk of oxidation. After a week, I took hydrometer measurements confirming both beers had reached the same FG.

I let the beers sit a few more days before confirming no change in FG and proceeding with packaging.

The filled kegs were placed in my keezer where they were burst carbonated overnight before I reduced the gas to serving pressure and left them alone for a lagering period. The first samples taken after 3 weeks revealed a rather noticeable difference in appearance.

Following a couple more weeks of lagering, the beers were equally carbonated and had taken on a more similar appearance.

| RESULTS |

A total of 21 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of the skimmed kräusen beer and 2 samples of the beer with the kräusen left intact in different colored opaque cups then asked to identify the unique sample. While 12 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, only 10 (p=0.12) did, indicating participants in this xBmt were unable to reliably distinguish a pale lager that had the kräusen removed during fermentation from one where the kräusen remained throughout fermentation.

My Impressions: Out of the 5 triangle tests I attempted, I identified the odd-beer-out every time, which was surprising. To me, both beers had the same aroma and flavor, the only thing I perceived as being different was a slight bitterness on the back of my tongue in the non-skimmed batch. While this wasn’t particularly unpleasant, I did somewhat prefer the skimmed batch, though they were so similar, I’m not sure I would have been able to tell them apart if I was going in blind.

| DISCUSSION |

Whereas some brewers aim to produce the best beer with the least effort possible, others are willing to engage in more arduous methods on the hope it’ll have some positive effect. The current paucity of talk surrounding the process of skimming kräusen during fermentation, particularly as a means of improved beer quality, seems to indicate it may not have much of a perceptible impact, which is supported by the results from this xBmt showing tasters could not reliably tell apart beers made with and without the kräusen skimmed.

There’s no denying kräusen contains dead yeast cells, hop compounds, and other perceptible compounds, though considering the results of this xBmt, it would seem it mostly gets left behind in the trub. Seeing as I was somehow able to consistently tell these beers apart, I’m left wondering if perhaps the some people may be more sensitive to the flavor impact of kräusen than others. Regardless, I have no plans to integrate this method into my normal brewing process, as the differences I perceived were slight and definitely not worth the extra effort.

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

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