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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How-to: Harvest yeast from starters
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30 thoughts on “exBEERiment | Impact Using Old Yeast Slurry Has On A Vienna Lager”
I recently went back to pitching sloppy slurry after my erlenmeyer flask cracked. I was able to rationalize it because I harvested yeast from low gravity and lightly hopped beers like an English Mild and Hefeweizen.
The convention with yeast harvesting has been that it is ideal to harvest yeast that hasn’t been stressed in an overly boozy or hoppy wort. An interesting experiment would be to harvest sloppy slurry from an IPA and compare it to fresh yeast to see if there is a noticeable difference.
Totally on the list!
In the basicbrewingradio podcast prior to the latest one you did with them, they interviewed Vinnie from Russian River and he mentioned that at about the 3rd harvest is when Pilsners are best. Wonder if this would be the same for your lager. He said they first build the fresh yeast with a steam beer, then take that “starter” and put it in the pilsner.
I still haven’t began reusing yeast, but I want to start soon. Cheers
I took note of Vinnie’s observation and absolutely plan to play around with it in upcoming xBmts. Cheers!
Flavor aside, wouldn’t “fresh” yeast be “less risky”, viability-wise?
I’m not sure that’s exactly the case since viability has only to do with the amount of live (ready to ferment) cells, which is arguably greater in a slug of harvested yeast than a small amount of “fresh” (or new) yeast.
Hey Brü,
how many packs of dry yeast did you use? As for Fermentis, they specifically state 2-3g/L for starting at temperatures around 9-10 °C. So for your batch that would be 3.7-5.4 packs. Maybe that was the reason for the big lag?
I purposefully used one pack since that’s what many homebrewers I talk to do and it works fine, it has many times for me in the past. Cheers!
Thanks for the info :). But wouldn’t it be more meaningful using the Fermentis guidelines for dry yeast when you even made a starter out of the slurry? In terms of comparability.
Some might think so, this time around I chose the more “popular” method. I believe I pitched 2 in the first slurry xBmt, fwiw.
I really like your blog and I try to perform some experiment like this myself. Thank you to take the time for all the brewers that follows your blog. But within the last year, I don’t recall experiments that shows major difference between 2 batches. I believe that youre brewing technics are so perfect, that when you try to modify one aspect of it, it’s not that significant on the final result. I know that’s a perfect way to address brewing dogma, to modify one thing at the time, but how come “regular” homebrewer always see major improvement when the start to control the fermentation step and when you do it’s always minor or nothing ? I’m wondering if your experiments are not only displaying the difference between a really good beer and a realy realy good beer ? So the judges can’t make the difference because some judges prefer beer more like this and the other more like that… Maybe the experiments results should be the difference between a bad beer and a realy realy bad one ? The difference would be stunning for the judges ? What do you think ?
I’m more inclined to believe bad beer is the result of multiple “poor practices” rather than a single variable… those xBmts are coming!
Are you planning to integrate 2 variables (or more) into one experiment ?
You better believe it! Just trying knock out some single variables first.
I have been having similar thoughts about these well run experiments. The big factors that could contribute to bad beer have all been dealt with already. I am thinking good quality, well modified malts, known good yeasts, fermentation temperature control, cleanliness, a good powerful boil and the use of dependable packaging process. I have a book that got me started in the brewing hobby many years ago that I enjoy reading as it reminds me how much homebrewing technology, equipment and ingredients have improved in the last 20 years. There is always room for improvement however so please continue with the fine work.
Hi Marshal,
Another interesting Beerexperiment.
I’ve noticed that one participant noticed diacetyl aroma in the dry yeast sample.
The pitch rates where quite different between the samples, as well as the diacetyl rest time.
Question:
1. At what temperature did you rehydrated the dry yeast?
2. At what temperature the dry yeast was when you pitched it in the cooled wort?
Congratulations for another good experiment,
Cheers,
Luis
Thanks!
1. Rehydrated at 85F for 15 min.
2. I placed it in chamber while hydrating, it was around 58F at pitch.
Hi,
Another nice exbeeriment. I have a few questions:
When you say 12 oz of dense slurry is all of you recollected ( slurry with his beer)?
Can you explain a little more about the calculations? Are 1.2 billion cels for ml and assume the half are no yeast material (how the other yeast slurry exbeeriment)?
I have fermented some batches that are good for me with slurry without starter using all the yeast slurry or 2/3 from the month ago batch ( maybe a big overpitching) (I would like to claculate the number of cells). Do you agree if use a more quantity of stored slurry is a good idea to avoid starter?
Thanks
From my understanding based on what I’ve read from authorities on the subject, dense slurry has ~1.2 bil cells per mL including all the trub material. I’m certainly no expert, but that calculation has been working fine for me.
I personally don’t think overpitching is something homebrewers have to worry about, I’ve got some xBmts planned to test it out. I’ve also got plans to test out using stored slurry without a starter, but at this point, I’ve never done it, so I can’t comment on it with any validity. Cheers!
Thanks for clarifying, I was going to ask about how you determined the initial cell count using the calculator that you linked to in the intro (or method?).
In terms of over pitching yeast, I am currently concerned about it, given that I mainly brew IPAs and it seems that yeast cells/membranes may act to bind with and scrub hop aroma oils (per the Janish research summary you have linked to elsewhere).
So if you end up doing an xbmt on over pitching, I would love to see it done with hoppy beer, since that may be where its effect shows up greatest. Thanks in advance for any additional thoughts on the matter!
As in REALLY overpitching? 😀
Hey Marshall – what about repitching a sloppy slurry that’s been hit with gelatin? Have you tried this? Just wondering since i have a 029 cake right now that i did a kolsch followed by a mocktoberfest on that cake. I did not pitch gelatin on the kolsch cake, but I did get lazy and pitch it on the mocktoberfest cake vs doing it in the keg like I did with the kolsch. Wondering if I should toss that cake since it’s been ‘gelatinized’, or if it would still be viable.
-R
I’ve only ever used sloppy slurry from beers previously fined with gelatin, it’s never been an issue!
I was wondering, was the sloppy slurry taken from a primary fermentation vessel or secondary? I’ve pretty much gone away from secondary fermentation but know there’s a lot more trub left with the yeast afterward. Don’t really care for rinsing the yeast either though. I have noticed in the past that when using harvested yeast from a higher gravity beer my percentage of attenuation went up. I believe that this may be caused because only the more alcohol resistant yeast cells survive, although it took a lot longer for fermentation to start. I am no expert about yeast at all though. I just like to brew beer, so it was just a thought. It would be interesting to test out in a more controlled atmosphere. Love the page, been following for about 6 months now.
The slurry was taken from primary, I never secondary. Thanks for the support!
Hi,
I’m a little confused; was your slurry 14 weeks old?
I have a sloppy slurry of WLP820 from a batch of Oktoberfest that I got from the primary (trub and all) sitting in my refrigerator that I plan to use for a Vienna lager and I’m wondering if it will be ok (or at least comparable to what you did here).
To be clear; I bought 4 vials of WLP820 and made a 3L starter and then pitched that into 9.5 gallons of Oktoberfest. I took no great pains to avoid transferring trub to primary (although the small amount of hops I did use were kept in a nylon bag during the boil). After primary fermentation was complete I moved it to secondary for a traditional lager (I know, I will definitely try the fast lager method). Then I took the entire contents from the bottom of my two primary fermenters and transferred to a sanitized 3L bottle and into the fridge.
I plan on “waking up” this sloppy slurry by first decanting the liquid on top and replacing it with about 1L of fresh starter wort (followed by several hours of stirring) prior to pitching into a Vienna Lager. The total time the sloppy slurry will have sat in my fridge is around 8 weeks.
Any advice would be greatly welcomed. I love this site!
Thanks.
Ken
That’s basically what undid and it worked great!
Great, can’t wait to make that Vienna lager and start saving sweet moolah on yeast!
Is it possible that the more attenuated feel from the slurry yeast is part in due with the yeast being more spent and looking for other nutrients in the wort to get proper and good fermentation?
I’d be interested in reading whether the same results apply to a batch fermented from a slurry with a proper addition of yeast nutrient compared to fresh yeast.
Cheers! As always, thanks for the read.
I mean, the beers were statistically indistinguishable, my impression could have been a function of bias. But perhaps that’s what it was.