Author: Marshall Schott

Ludwig Narziss, largely recognized as one of the world’s foremost brewing experts, recommends wort be separated from kettle trub prior to fermentation in order to produce the best tasting product. Using a mechanical filtration system is the only way to eliminate trub from wort, but due to how unreasonably cumbersome such a process is, brewers tend to rely on simpler methods to reduce the amount of trub in their wort such as racking to the fermentation vessel after a period of settling.

With the effort many invest in trub removal, it’s surprising how little consensus there is on how it actually impacts beer. There are those who contend the gooey gunk imparts a “yeasty” off-flavor, while others seem more concerned with its role on clarity. But ultimately, any attempt to grasp the gestalt of kettle trub hatred left me convinced the parts may not necessarily add up to a greater whole.

Indeed, there’s evidence suggesting the terror over trub may not be necessary, that it has no effect on flavor and may in fact positively contribute to healthy fermentation. Corroborating this notion are our past xBmts demonstrating higher amounts of kettle trub not only led to more vigorous fermentation with faster attenuation, but that it had little if any perceptible impact.

One thing both prior xBmts had in common is that the beers were packaged and consumed relatively soon after being brewed, causing some to wonder if the time on trub might have a greater effect. I was curious to find out!

| PURPOSE |

To evaluate the impact the amount of kettle trub during fermentation has on German Pilsner fermented cool and aged in primary for an extended period of time.

| METHODS |

The recipe I settled on for this particular xBmt was a simple one that would mark my first time using Mecca Grade Estate Malt, with Pelton making up the large majority of the grist.

Pheurton

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 31.5 IBUs 3.9 SRM 1.051 1.014 4.8 % Actuals 1.051 1.011 5.2 % Fermentables Name Amount % Pelton (Mecca Grade) 9.625 lbs 90.59 Vanora (Mecca Grade) 1 lbs 9.41 Hops Name Amount Time Use Form Alpha % Perle 12.5 g 60 min First Wort Pellet 8.3 Perle 15 g 30 min Boil Pellet 8.3 Perle 30 g 5 min Boil Pellet 8.3 Perle 30 g 3 days Dry Hop Pellet 8.3 Notes Water Profile: Ca 75 | Mg 1 | Na 10 | SO4 84 | Cl 70 | pH 5.5 Download Download this recipe's BeerXML file

Since these lagers would be fermented cool, I made a single large starter with 2 packs of Imperial Yeast L13 Global 3 days ahead of time.

After moving the fully fermented starter to my garage fridge 2 days later to cold crash, I moved on to weighing out and and milling the grain for a single 10 gallon batch.

I then collected the full volume of filtered water and adjusted it to my desired profile, after which I dropped my heat stick in, put the MLT cover in place, and set my timer to turn on a few hours before I planned to brew the following morning.

With my strike water at the right temperature the following morning, my kids helped me mash in before heading off to school.

A check of the mash temperature once the grains were fully incorporated showed I was right where I wanted to be.

I replaced the lid and let the mash rest for an hour, stirring every 20 minutes to encourage conversion, before collecting the sweet wort.

The wort was boiled for 60 minutes with hops added at the times stated in the recipe.

When the boil was finished, I quickly chilled the wort to 70°F/21°C, which was slightly warmer than my groundwater temperature at the time.

After confirming the wort hit my target 1.051 OG, I placed a piece of wood beneath the front edge of my kettle so that the hops and break material would settle toward the back.

After 15 minutes of settling, I filled the first carboy with very clear wort. Then I removed the wood and began filling the second carboy, using a sanitized spoon to coax as much trub as possible out of the kettle. Mission accomplished.

For fun, I took a time-lapse video of the worts over the course of about 20 minutes to observe the trub settling.

The carboys were placed next to each other in my chamber and allowed to finish chilling to my target fermentation temperature of 50°F/10˚C, which took about 7 hours, at which point I split the decanted starter equally between the batches. Unlike previous observations, the high kettle trub batch didn’t seem to start fermenting any sooner than the low trub beer. However, it did appear to ferment with more vigor as evidenced by more observable airlock activity and quicker falling of the kräusen.

Hydrometer measurements 2 weeks after yeast pitch revealed the low trub batch was a bit behind the high trub beer.

At this point I added the dry hop addition then let the beers remain at 50°F/10°C for another week before taking a second set of hydrometer measurements showing the high trub beer had reached FG while the low trub beer hadn’t changed much at all. Seeing as it had been 3 weeks, I raised the temperature of the chamber to 60°F/16°C in hopes of encouraging complete attenuation. After another week, 4 total since pitching the yeast, the low trub beer was sitting at the same 1.011 FG as the high trub beer.

To reduce the risk of oxidation, I kegged the beers without first cold crashing them, making note of the trub at the bottom of each carboy.

Skipping my typical gelatin fining process, the filled kegs were placed in my cool keezer on gas to carbonate. I stole some samples to satiate my curiosity a week later and noticed the beers looked quite a bit different.

I finally began collecting data 4 weeks later, 5 since packaging, and noticed time didn’t seem to have much of an impact on appearance.

| RESULTS |

A total of 20 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the low kettle trub beer and 1 sample of the high kettle trub beer in different colored opaque cups then asked to identify the unique sample. At this sample size, 11 tasters (p<0.05) would have had to identify the unique sample in order to reach statistical significance, while a total of 13 (p=0.004) made the accurate selection, indicating participants in this xBmt were able to reliably distinguish a Pilsner fermented with a lot of kettle trub from one fermented with very little kettle trub after a period of aging.

The 13 participants who made the accurate selection on the triangle test were instructed to complete a brief preference survey comparing only the beers that were different. A total of 7 reported preferring the low kettle trub beer, 2 liked the high kettle trub beer more, 3 had no preference despite noticing a difference, and 1 person reported they perceived no difference between the beers.

My Impressions: Even after 15 years, I still get excited about every batch I brew and look forward to tasting the hydrometer samples. In doing so with these beers, it was pretty obvious to me they were different, which certainly could be explained by bias. Except in a series of triangle tests served to me by others, I identified the odd-beer-out on all 7 of my attempts. I’m not sure if how to describe the aroma and flavor I perceived in the high trub beer that was absent in the low trub beer, it was just different, noticeably so. The best I could come up with was “flubber,” which I’ve never actually tasted, it’s just what I imagine it tastes like. While I definitely preferred the low trub beer, I didn’t have a problem finishing off both kegs, though I’d be inclined to not shove such a large amount of trub in my fermentor in the future.

| DISCUSSION |

In Principals of Brewing Science, George Fix explains that while the high amount of unsaturated fatty acids in kettle trub “contribute to yeast viability” and “inhibit the formation of some less pleasant acetate esters,” they also negatively impact head formation and, even worse, expedite beer staling. He goes on to say that these issues are due to how resistant these unsaturated fatty acids are to oxidation, hence they “spill over into the finished beer where they tend to produce fatty or goaty notes.”

The observations during this and prior xBmts on the same topic corroborate claims that higher amounts of kettle trub encourage more vigorous and quicker fermentation. Where this xBmt differs from those in the past is in the fact participants were capable of reliably distinguishing the high kettle trub beer from the low kettle trub beer, and most preferred the latter.

Considering the first 2 kettle trub xBmts were packaged 13 and 18 days after yeast pitch, it’s plausible the amount of time beer spends in contact with trub has an impact. If this is in fact true, then it stands to reason that the beer fermented with a high amount of kettle trub may not have developed those distinguishing characteristics had it not been in contact with the trub for as long as it was. For the third time now, we’ve demonstrated that kettle trub seems to be beneficial for fermentation, perhaps racking moderate amounts to the fermentor and packaging when fermentation is complete is the best of both worlds.

As for me and my brewing, these results haven’t motivated me to make any drastic changes, I’ll continue not worrying too much about what makes it to my fermentors without intentionally moving all the trub over, as I appreciate the impact it has on both fermentation and clarity. I am curious to explore the effect oxygenation and gelatin fining have on beers fermented with low amounts of trub. Things to come!

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

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