Author: Marshall Schott

Back when Northshore was still a junior high and had an offensive mascot, us students were required to participate in a weekly “Wednesday Run” where we had about 30 minutes to complete a 1.25 mile/2 km course around the school. I was unfortunate enough to have PE 5th period, the second to last class of the day, which not only meant my 6th period classmates had to deal the consequences of my insecurity-derived avoidance of group showers, but it was after lunch where I usually spent 20 minutes sprinting my chubby ass up and down a basketball court pretending to be the next Gary Payton. Needless to say, when it came time to run, I was already exhausted and often resorted to walking the track with a curiously entertaining group of other kids.

This experience is what comes to mind when I consider the commonly recommended method for reusing yeast. The claim goes that it’s best to pitch slurry from a lower OG beer into a higher OG beer because going in the opposite direction can lead to off-flavors caused by stressed, or exhausted, yeast. In essence, we want our yeast running the track, not walking it with a bunch of other lazy cells.

I realized my opportunity to finally test this variable out while I was kegging a Barleywine I recently brewed. At 1.099 OG, it’s safe to say the yeasts worked their tails off to ferment that beer, so I harvested some slurry and prepared for my next xBmt!

| PURPOSE |

To evaluate the differences between Blonde Ales fermented with either a fresh pitch of yeast or slurry of the same strain that was previously used to ferment a 1.099 OG Barlewine.

| METHODS |

Wanting to make sure any impact of the variable wasn’t hidden by other ingredients, I designed a simple Blonde Ale with a moderate OG and minimal hop additions.

Leister

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 30 min 21.7 IBUs 5.8 SRM 1.048 1.011 4.9 % Actuals 1.048 1.007 5.4 % Fermentables Name Amount % Lamonta (Mecca Grade) 9 lbs 85.71 Metolius (Mecca Grade) 1.5 lbs 14.29 Hops Name Amount Time Use Form Alpha % Centennial 7 g 30 min First Wort Pellet 9 Simcoe 7 g 20 min Boil Pellet 13.1 Centennial 7 g 10 min Boil Pellet 9 Simcoe 7 g 10 min Boil Pellet 13.1 Centennial 4 g 5 min Boil Pellet 9 Simcoe 4 g 5 min Boil Pellet 13.1 Yeast Name Lab Attenuation Temperature Flagship (A07) Imperial Yeast 75% 60°F - 72°F Notes Water Profile: Ca 75 | Mg 1 | Na 10 | SO4 114 | Cl 49 Download Download this recipe's BeerXML file

While the Barleywine was being transferred to a keg, I hit the internet and found I’d need approximately 400 mL of dense yeast slurry to match the 200 billion cells in a pack of Imperial Yeast. Once the keg was filled, I swirled the remnant beer in the fermentor then filled a 1 quart mason jar with the loose slurry and put it in the fridge. The following day, I found the slurry had compacted to almost exactly 400 mL– nice!

Later that evening, I collected my water for the following morning’s brew.

While the water was slowly running through the filter, I weighed out and milled the grains.

After adjusting the water to my desired profile, I dropped my heat stick in and set it on a timer to turn on a couple hours before I woke up the next day.

Greeting me the following morning was hot strike water, which I gently added the milled grain to.

The temperature ended up settling just a hair below my target due my impatience, nothing I was concerned over.

I stole a small sample of wort about 15 minutes into the mash and chilled it down before taking a pH reading showing things were right on track.

Toward the end of the mash rest, I measured out the small amount of hops that would be used in this batch.

At the end of the 60 minute mash, I collected the sweet wort in a graduated bucket then transferred it to my kettle.

I lit the burner then moved on to cleaning my mash tun while the wort was heating up.

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

Once the boil was complete, I quickly chilled the wort to slightly warmer than my groundwater temperature.

A refractometer reading showed I hit my target 1.048 OG.

I then filled separate Brew Buckets with identical amounts of wort.

The fermentors were placed in my temperature controlled chamber to finish chilling, at which point I split 1000 mL of leftover wort between a couple growlers, pitching the fresh pack of Imperial Yeast A07 Flagship into one and the slurry into the other.

I returned 4 hours later and found both worts had stabilized at my target fermentation temperature of 66°F/19°C, so I pitched the vitality starters and connected my CO2 harvesters.

I heard bubbling coming from my chamber later that evening and decided to take a peak under the hood. I found the slurry pitched beer had already developed a solid kräusen while the fresh yeast batch was just getting going. Pretty impressive for just 8 hours post-pitch.

I raised the temperature of the chamber to 72°F/22°C 4 days into fermentation to encourage complete attenuation. After another 3 days, I took hydrometer measurements confirming both beers had reached FG.

I cold crashed the beers and fined them gelatin before proceeding with transferring them to CO2 purged kegs.

The filled kegs were placed in my cool keezer and burst carbonated. After a day at 50 psi, I reduced the gas to serving pressure and let the beers cold condition for 6 days before moving forward with data collection.

| RESULTS |

A total of 21 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of the beer fermented with fresh yeast and 2 samples of the beer fermented with slurry previously used to ferment a high OG batch 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 exactly how many were able to do so (p=0.021), indicating participants in this xBmt could reliably distinguish a Blonde Ale fermented with a fresh pitch of Imperial A07 Flagship yeast from one fermented with the same strain previously used to ferment a 1.099 OG Barleywine.

The 12 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 tasters reported preferring the beer fermented with fresh yeast, 4 said they liked the beer fermented with the high OG slurry, and 1 taster reported perceiving no difference.

My Impressions: When tasting they FG hydrometer samples for these beers, I was pretty sure I could detect a difference, though it was slight enough that I assumed it’d disappear after a period of cold conditioning. Nope. Out of the 8 semi-blind triangle tests I attempted, I accurately identified the unique sample 6 times, and in each case I made my determination primarily based on aroma. Whereas the beer fermented with fresh yeast smelled like a pretty standard pub-style Blonde Ale, the one pitched with high OG slurry had a sort of rubbery thing going on. It certainly wasn’t overwhelming, the beers were way more alike than they were different, but the aromatic difference was at least noticeable. As far as flavor goes, the beers tasted nearly identical to me– clean and malt forward with just a hint of American hop character.

| DISCUSSION |

With most commercial yeast labs providing limited cell counts, one approach to ensuring adequate pitch rates involves reusing yeast from one batch to ferment another batch, which also happens to be pretty cheap. Given the stress put on yeast during the fermentation process, a common recommendation is to only repitch slurry that was used to ferment a beer with a lower OG than the new batch in order to prevent off-flavors. Blonde Ale to IPA to Barleywine. Something like that.

I generally trust science more than hunches, though I’ve occasionally questioned the logic of this recommendation and wondered just what could come from pitching a proper amount of slurry from a big beer into another batch. It seemed to my microbiologically ignorant mind that any byproducts of stressed yeast would present in the original beer, and if they weren’t there, the yeast would do fine in the less stressful environment of a lower OG beer. Shining a light on my naïveté, tasters in this xBmt were indeed capable of distinguishing a Blonde Ale fermented with Barleywine yeast slurry from one fermented with fresh yeast.

In considering the implications of these results, I can’t help but think of the fact the aforementioned advice is provided as a way to avoid producing crappy beer. Thing is, the differences between the samples were really subtle, and while the fresh yeast version won the preference of more tasters, the beer fermented with Barleywine slurry was in no way bad. I say this not as advocacy for the practice, I’ll likely never do it again, but in a pinch, I think it’s a decent approach that will likely produce a perfectly fine beer.

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

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