Author: Marshall Schott

Harvesting yeast directly from the bottom of a fermentor was something I’d been afraid to try for years, fearing flavor carryover, yeast autolysis, and even overpitching, despite knowing of many trusted sources who swore by the method. Then I performed the first sloppy slurry xBmt that demonstrated tasters were unable to reliably distinguish a beer fermented with unrinsed slurry from one fermented with a fresh vial. What a simple and cheap trick– steal a pint or so of yeast from the bottom of a fermentor, toss it into a new batch of wort, and you’re good to go!

Sometime after publishing that article, I was contacted by a dude who shared with me something he’d heard– that unrinsed slurry has a significantly reduced shelf life compared to fresh or even rinsed yeast. This didn’t make much sense to me, so I did some poking around. Predictably, what I discovered was heaps of random and contradictory anecdotal evidence ranging from “it worked perfect” to “it fucking sucked,” leaving me with only one obvious option– test it for myself!

| PURPOSE |

To evaluate the differences between a split batch of the same wort fermented with either a 3rd generation of unrinsed yeast harvested from a prior batch and propagated in a starter or a fresh pitch of hydrated dry yeast.

Quick point of clarification: I intentionally chose to compare fresh yeast to a starter of previously harvested yeast in an attempt to equate viability. We absolutely plan to repeat this xBmt sans starter, I promise.

| METHOD |

In an attempt to hone my Vienna Lager recipe in order to kick the asses of Derek and Dan, I chose to brew a new version for this xBmt.

Vienna Lager #3

Batch Size Boil Time IBU SRM OG FG ABV 11 gal 60 min 23.8 11 1.050 1.010 5.2 %

Fermentables

Name Amount % Gambrinus Vienna Malt 7.5 lbs 40% Gambrinus Munich 10 Malt 7.5 lbs 40% Belgian Pils Malt 3 lbs 16% CaraPils 6 oz 2% Melanoidin Malt 3 oz 1% Midnight Wheat 3 oz 1%

Hops

Name Amt/IBU Time Use Form Alpha % Tettnanger ~21 IBU (44 g) FWH Boil Pellet 5.8% Tettnanger 30 g/2.6 IBU 15 min Boil Pellet 5.8%

Yeast

Name Lab Attenuation Ferm Temp SafLager W-34/70 Fermentis 80% 50°F

Water Profile

Ca Mg Na SO4 Cl HCO3 pH 78 ppm 1 ppm 10 ppm 88 ppm 73 ppm 33 ppm 5.3

Based on the approximate amount of dense slurry (~12 oz), the age of the yeast (14 weeks), and the OG of the wort, I determined the starter starter size using my preferred calculator and got it spinning 2 days ahead of time. The starter behaved much different than any I’ve ever made, which was disconcerting, I wondered if perhaps it had kicked the bucket… brewers never say die!

I woke up bright and early a few days later and got the flame going on the strike water I’d collected the night before. Once to temp, I mashed in, stirred for about a minute to fully incorporate the grist, confirmed I hit my target mash temp, then closed the lid.

I allowed the grains to mash for an hour, giving them a couple hasty stirs every 20 minutes or so.

I collected the first runnings, admiring the gorgeous amber color and rich aroma of Gambrinus’ remarkable Vienna malt.

I proceeded to boil the wort for an hour, adding hops along the way, then it came time to chill– 212°F to 76°F (6°F above groundwater) in under 12 minutes.

Once cool, the wort was split evenly between two 6 gallon PET carboys, stirring gently to ensure equal distribution of kettle trub.

I placed both full carboys in a fermentation chamber controlled to my target fermentation temperature of 50°F, it took about 6 hours for them to chill completely, at which point I pitched the decanted sloppy old slurry starter into one and the rehydrated fresh yeast into the other.

It didn’t take long for my fears to be assuaged, as the sloppy old slurry batch was rocking less than 24 hours post-pitch. Ahhh.

I’ve come to expect relatively long lag times when pitching fresh packs of dry yeast, which is exactly what happened in this case– at 2 days in, the fresh pack batch appeared completely inactive.

It was until 3 days after pitching that I noticed any signs of activity in the fresh pack batch, and even them it was scant.

Just as the fresh pack batch really started kicking, the sloppy old slurry batch began to slow down, which led me to change the fermentation schedule I typically use with traditional lager strains.

I figured it’d be most prudent to wait until the fresh pack batch dropped in activity before raising the temps, which took another 3 days, at which point I ramped for a 5 day diacetyl rest.

I took an initial FG measurement at 2 weeks in followed by a confirmatory reading 3 days later.

Both beers finished at my 1.010 SG target and were free of any detectable diacetyl, so I cold crashed, fined with gelatin, racked to kegs, then put them in my keezer to carbonate. By serving time, both beers had cleared up nicely.

| RESULTS |

The participant pool for this xBmt consisted of 18 people including BJCP judges, experienced homebrewers, and dedicated craft beer drinkers. Each person was blindly served 3 samples, 2 fermented with a starter of sloppy old 34/70 slurry and 1 fermented with fresh yeast, then asked to select the one they believed was unique from the others.

In order to achieve statistical significance, 10 (p<0.05) participants would have had to correctly identify the fresh yeast beer as being different, though only 9 (p=0.067) were capable of doing so.

That’s pretty damn close, at least enough to cause some to wonder if perhaps the difference is palpable, if fermenting with unrinsed old yeast that previously fermented a couple batches produces a beer qualitatively different than a beer fermented with fresh yeast. Of course, it’s possible a larger sample size would have pushed this into the realm of statistical significance, though the opposite is also possible. Regardless, given how close this one was, sharing the comparative evaluation data of those who were correct in the triangle test seems the most prudent approach, just please interpret with caution.

The 9 folks who correctly identified the odd-beer-out in the triangle test were then asked to compare only the 2 different beers, still unaware of the nature of the xBmt.

AROMA

Only 1 taster experienced the aroma of the beers to be not at all similar and the other 8 thought they were somewhat similar; the sloppy old slurry beer was described as being more bready with a richer and sweeter malt character, while one taster noted the fresh yeast beer to have “noticeable diacetyl.” Twice as many tasters (6) preferred the aroma of the beer fermented with the starter of sloppy old slurry as did the fresh yeast batch (3).

FLAVOR

All 9 participants noted the beers to be somewhat similar in regards to flavor with 2 tasters commenting that the fresh yeast beer had a “more complex malt profile” and a “much stronger malt flavor,” while the sloppy old slurry beer was described as having a “sharper finish.” Preference was split with 5 and 4 endorsing the sloppy old slurry beer and fresh yeast beers, respectively.

MOUTHFEEL

Two tasters felt the mouthfeel of the beers was exactly the same, 5 thought they were somewhat similar, and 2 perceived them as being not at all similar. Of the 7 who noted some similarities, 5 preferred the mouthfeel of the sloppy old slurry batch.

As far as overall preference, 5 of the 9 tasters selected the sloppy old slurry beer and 4 preferred the fresh yeast beer. Once the nature of the xBmt was revealed, tasters were asked to guess which one they believed was fermented with fresh yeast– 4 chose correctly.

My Impressions: I only triangle tested myself once with this batch, and I was right, though I’m compelled to believe a part of my ability to distinguish between the beers had to do with my knowledge of the variable being tested along with my experience drinking these beers daily. Similar to some of the comments, I perceived the fresh yeast batch as being ever so slightly more malty with subtly more melanoidin character, almost Märzen-like, while I experience the sloppy old slurry beer as being crisper, as if it had attenuated more despite finishing at the same SG. Really though, they are remarkably similar.

So, how was the beer?

It’s good, not quite there yet, but tasty and easy-drinking. This 3rd iteration is definitely closer to my ideal Vienna Lager, just slightly too malty rich, likely from the large percentage of Munich malt used. For my next batch, I plan to replace the Munich malt with mostly German Pils and maybe a touch more Vienna, add a touch of Victory Malt for a subtle biscuit character, and ferment with a different yeast… or 2 🙂

| DISCUSSION |

The fact we failed to reach statistical significance might lead some to conclude unrinsed old yeast propagated in a starter works just as well as fresh yeast, which sort of misses the actual purpose of the xBmt. Rather, this data only serves to support the notion that in this particular incidence, sloppy old yeast produced a beer similar enough to a fresh pack of the same strain that a significant portion of tasters we unable to reliably distinguish between them. But it was pretty close. Having compared these beers multiple times, I’m comfortable saying the difference wasn’t stark enough that, if served one after the other, I wouldn’t notice the switch. Even if significance had been reached, it’d speak nothing to the quality of the beers, that’s up to each individual drinker to decide for themselves.

While I’m hesitant to say anything that might remotely come across as a recommendation, these results combined with those from the first slurry xBmt have served to weaken my conviction that “clean” yeast is necessary for good beer, I certainly plan to continue pitching unrinsed slurry, not for any flavor or aroma impact, but because it’s easy. I’d personally opine that, given good sanitation practices, fermenting with sloppy yeast harvested from the bottom of a carboy will not impart off-flavors, which feels slightly odd to admit since I’ve been an advocate for harvesting clean yeast from starters for so long.

I absolutely plan to continue playing with this variable and am particularly interested to see how things end up when I reuse yeast from a highly dry hopped batch, as well as yeast harvested from the trub of a high OG beer. Until then, feel free to share your experiences in the comments section below.

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| Read More |

18 Ideas to Help Simplify Your Brew Day

7 Considerations for Making Better Homebrew

List of completed exBEERiments

How-to: Harvest yeast from starters

How-to: Make a lager in less than a month

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