Author: Marshall Schott
I personally think it (harvesting yeast from starters) is much easier and far less time consuming [than rinsing yeast]. Additionally, the yeast fermented a wort of ~1.040 OG that had no hops in it, so it is arguably less stressed and ultimately cleaner.
~ From the F.A.Q. section of my Yeast Harvesting page ~
I’ve tried my hand at yeast rinsing and, besides experiencing it as too time-consuming of a process, all the transfers and water additions seemed to increase the chances of picking up an unwanted infection. I wanted a way to be cheap that required less time, effort, and risk. Overbuilding and harvesting yeast from starters was my solution. It just made sense to me that this method would produce a superior pitch of yeast that was less likely to experience generational drift compared to yeast going through multiple fermentations and rinses. I reckon many would agree that it has worked great! But, it’s not the only way.
Soon after I first published the aforementioned article, I began fielding questions about other methods for harvesting and reusing yeast. One approach that regularly popped up involved racking chilled wort directly onto a yeast cake that had recently fermented another batch of beer, usually into the same fermentor, and there seemed to be quite a few homebrewers achieving great results doing this. One of the more commonly cited concerns with this method has to do with the potential for over-pitching, something I question the validity of, at least on the homebrew scale. I have tried fermenting on a used yeast cake, it worked fine, it just lacked the level of precision my neurotic mind desires. Another fairly similar option I’d heard about involved pulling off a sample of a freshly used yeast slurry and pitching that into a new batch of wort, forgoing the whole rinsing procedure. Still somewhat concerned about the impact the other junk suspended in the slurry might have on my finished beer, I was at least intrigued enough by the simplicity of this method to give it a shot.
| PURPOSE |
To investigate the differences between 2 beers fermented with the same strain of yeast, one originating from the slurry of a prior batch and the other propagated in a starter from “clean” yeast.
| METHOD |
I decided to perform this xBmt a few days before kegging the Schwarzbier batches from the fermentation temperature xBmt, as this would allow me to reuse that WLP029 yeast, which I’ve had great experience with in lager styles. I also like that the yeast was coming from a very dark beer, something I’ve heard others pooh-pooh in the past, and that I’d be pitching the slurry into fresh wort just hours after harvesting. I figured a simple German Pils would be a good beer for this xBmt, reasoning any differences would be much easier to recognize in such a light style.
German Pils
| Batch Size | Boil Time | IBU | SRM | OG | FG | ABV |
|---|---|---|---|---|---|---|
| 11 gal | 90 min | 36 | 3.4 | 1.050 SG | 1.012 SG | 5.0 % |
Fermentables
| Name | Amount | % |
|---|---|---|
| Belgian Pils Malt | 17 lbs | 94.4 |
| Gambrinus Vienna Malt | 1 lbs | 5.6 |
Hops
| Name | Amt/IBU | Time | Use | Form | Alpha % |
|---|---|---|---|---|---|
| German Perle | ~26 IBU | 60 min | Boil | Pellet | 8.6 |
| Hallertauer Mittelfrüh | 45 g/5.7 IBU | 15 min | Boil | Pellet | 6.3 |
| Tettnanger | 60 g/4.4 IBU | 2 min | Boil | Pellet | 8.9 |
Yeast
| Name | Lab | Attenuation | Ferm Temp |
|---|---|---|---|
| WLP029 German Ale/Kölsch | White Labs | 76% | 58°F |
Using a trusted yeast pitch calculator, I determined a 1L starter would lead to approximately 280 billion cells, slightly more than recommended due to the cooler fermentation temperature I prefer when using WLP029 for lager styles.
Calculating the amount of slurry required to come close to a similar cell count wasn’t terribly difficult. Assuming dense yeast slurry contains roughly 1.2 billion cells per ml (1, 2) and aiming for a total cell count of 280bil to match my starter, I ended up collecting a full pint (~473 ml) of loose slurry from the bottom of the cool fermented Schwarzbier carboy, understanding the actual yeast would ultimately compact to about half of this volume. By my calculations, this would leave me with approximately 284bil cells: (473 x 0.5)1.2 = 283.8. Perfect!
Well, maybe not perfect. Harvesting yeast is a fairly inexact science, one I wish was a bit more precise. Good enough would have to do! It was time to make some wort, which was pale as ever due to the simple grain bill of only Belgian Pils and Vienna malts.
I boiled for 90 minutes because that’s what I’ve heard I’m supposed to do to reduce the chances of DMS off-flavors when the grist consists of mostly Pilsner malt, an admitted appeal to authority (xBmt planned). I then chilled the wort to my target fermentation temp of 58°F in less than 10 minutes.
Two 6 gallon PET carboys were filled, placed in a 58°F fermentation chamber, and the yeast was pitched– decanted starter in one, slurry in the other. Visible activity was observed a mere 6 hours later.
The following morning, I noticed the krausen on the slurry batch had some darker brown spotting, something I’m guessing was caused by the fact the yeast was previously used to ferment a Schwarzbier. Would this have a noticeable impact on the finished beer?
Fermentation proceeded at about the same pace for both beers and they began to look much more similar a few days in.
By day 8, the batch pitched with a starter still had some krausen resting atop the beer, while the krausen on the slurry batch had all but disappeared.
With neither beer showing visible signs of fermentation at this point, I took a hydrometer sample and found both had attenuated to my target FG.
I let the beers sit another day before taking another FG measurement (no change), cold crashing, fining with gelatin, and kegging.
The beers were crystal clear, carbonated, and ready for evaluation just a few days later.
| RESULTS |
Similar to the recent Cal Common yeast xBmt, most of the data for this one was collected while I was in the Bay Area following my appearance on The Brewing Network’s Dr. Homebrew show. As I’ve become accustomed to doing, I sought participants at nearly every beer-related establishment my buddies and I visited including the Concord MoreBeer location and Heretic Brewing Company in Fairfield. I can’t thank the cool folks that run these places enough for allowing me access to their customers for my silly xBmts. A special shout-out to the wonderful Liz Zainasheff, wife of Jamil and co-owner of Heretic Brewing, who I’m pretty sure had to let someone from a neighboring business know that I wasn’t hawking alcohol from the trunk of my Camry… embarrassing barely begins to describe how I felt. I apologized profusely to Liz, she shrugged it off with a smile, pointed me to a more concealed area of the brewery, and encouraged me to proceed. What a rad place!
A total of 13 people participated in this xBmt, 8 of which would have to accurately select the different beer to imply statistical significance (p<0.05). Each taster was blindly provided 2 samples of the beer feremented with a yeast starter and 1 sample of the beer fermented with May The Schwarzbier With You slurry. Five participants accurately chose the slurry fermented beer as being different while the majority (8) chose either of the other 2 beers. Statistically, the null hypothesis was supported, meaning the difference between low-moderate OG beers fermented with WLP029 propagated in a starter versus yeast stolen from a used cake is not discernible by the general population.
My Impressions: I’m often swapping beer lines in my keezer since it holds 7 kegs but I’ve only 5 faucets. When I do these swaps, I rarely change the name associated with each faucet/beer on the chalkboard lid, as I know I’ll eventually re-connect that keg later on; every keg is marked, so it’s not like I lose track of what xBmt beers are in which keg, something I triple-check prior to administering the actual test. Anyway, a couple days after I’d completed data collection, I did some keg swapping, as I wanted to try a freshly kegged beer. At some point, I moved the disconnect from the yeast starter keg to the slurry keg, then moved the disconnect that was on the new keg (originally on the slurry keg) to the yeast starter keg. Follow? Basically, the faucet I thought was serving the yeast starter beer was actually serving the slurry beer, and vice versa. Okay…
I began drinking these beers about a week before data collection began, I couldn’t get enough, I thought they were so good. While not tested blindly, I did compare the beers next to each other on multiple occasions and quickly developed a preference for the one fermented with the yeast starter, I thought it tasted cleaner, crisper, and generally better. This was about a week before data collection began and any line swapping occurred (again, this only happened after the last participant completed the survey). Given my preference for the yeast starter beer, I kept pouring from that tap until the keg finally kicked. It was only when removing the empty keg from my keezer that I realized I had in fact been drinking, and preferring, the slurry fermented beer.
Bias in action.
I couldn’t help but laugh at my own self-delusion as I recalled haphazardly swapping the lines a few days prior. Duh. I’d actually convinced myself that I preferred each beer over the other at different points, assuming the preferred beer had remained the same the entire time. It stung a bit to admit to myself that I likely wanted the yeast starter beer to be better because of the energy I’ve invested in advocating for a particular yeast harvesting method. It wasn’t conscious, if so I likely would have avoided this xBmt altogether; rather, my biased preference appears to have been driven by something deeper, some motive out of my awareness. The beers, for all intents and purposes, were the same. I obviously couldn’t tell them apart.
| DISCUSSION |
While I’m not quite prepared to replace harvesting from starters with pitching “sloppy” slurry from a prior batch, it would appear the practice can in fact produce great beer, even when the slurry previously fermented was very dark beer. Of course, this is only a single data point and these results may not necessarily carryover into other situations. I’m sure there will be at least a few who, after reading these results, will suggest that I should have pitched slurry that fermented a higher OG wort or compared starter yeast to washed/rinsed yeast. Good ideas, indeed, both of which I promise to eventually get to, but that wasn’t what this xBmt was about. Rather, I was interested in comparing a sloppier approach to harvesting versus a more controlled one, and to that end, I think we done good.
If you’ve any thoughts you’d like to share about yeast harvesting methods, please share them in the comments section below. Cheers!
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61 thoughts on “exBEERiment | Yeast Slurry vs. Clean Starter In A German Pils”
Awesome! I am a sloppy slurry pitcher fan and do so when I can.
Great experiment as always. What I do is basically both methods. I’ve read in the Yeast book that you don’t want to use non-washed, harvested yeast slurry after 2 weeks. Since I don’t brew as much as you and sometimes I switch to a different yeast, but if I can plan it correctly and it’s been less than 2 weeks, I will pitch a portion of the slurry into the next beer. Never had an issue doing it that way. But if I don’t have a slurry ready or want to use a different yeast, I always make a larger starter and save a portion for reuse. So when I can, you can’t beat the simplicity of reusing slurry, but when I can’t harvesting from a starter is a great way to save a few bucks.
Awesome exBEERiment , this has been something I have wondered about. Thanks for the great write up and your passion in brewing science.. Very cool..
Good read. I’m working on a low cost session blonde and will use this to shave a few dollars off my next batch. If my aseptic technique is good, you think I would be ok to keep a quart in fridge for a few weeks?
I’ve read you don’t want to store slurry too long… but I question that. Maybe if you let it come back up to temp before pitching it’ll work fine, but I’ve never tried.
As always, excellent experiment. I store slurry in jars for months, then brew day I take them out, bring to room temp, pitch. Not very scientific, but never had a problem with them so far (I’ve probably done it 20-30 times). To harvest the yeast, on bottling day, after I bottle, I sterilize some jars, shake the slurry up, pour into jars, refrigerate. easy (note: my bottling bucket is also my fermenter).
From what I have read, if you let the slurry come back to temp before pitching, the yeast will deplete their trehalose stores and you will get a lag while they recover in the wort.
I have experienced that, so next time I will pitch it cold.
Interesting. I’ve read that it’s important to bring the yeast within 10-15˚F of the wort temp before pitching. I’m curious how you know you’ve experienced depleted trehalose?
Just tried pitching slurry for the first time this past weekend. I kept a saison 3711 slurry in the fridge for about a month, took it out the day before, and kept it in the kitchen for about 24h before pitching. I split the batch – pitched rehydrated Nottingham into the other half – and 12 hours later both hand a nice inch of Krausen. No taste test yet, but the yeast doesn’t seem to have been bothered by a month of refrigeration, or by sitting at room temperature for a day.
Very cool!
http://www.danstaryeast.com/articles/pitching-temperature-and-nutrients
Is where I started, and googling led me to read some research papers about Trehalose function in yeast.
Yes, I read the link. Very interesting – next time I’ll pitch the yeast slurry cold right from the fridge and see what the lag time is rather than letting it warm up a day or so first.
I’ve used harvested yeast after a year of storage. Just threw it in a starter but it takes 3 or 4 days to take off sometimes. I’ve never had an infection or off flavor from this method.
Yes, I’ve gone out to 2 weeks without a problem.
I did a bunch and they were fine for over a month. Somewhere over that (it may have been two months?) I pitched one of the jars and it was taking a long time so I pitched some dry yeast in to give a hand. Nothing “bad” happened but I will not aim for over a month in the future.
Pitching direct on the cake has also worked, I just am usually not ready to brew then.
Here’s what they said in “Yeast”:
“Fresh is best. Keep storage time to a minimum. Yeast stored at 33 to 36° F (1 to 2° C) and used within seven days of collection is the goal. Consider 14 days the maximum storage time. Monitor the pH of the yeast slurry while in storage. A pH rise of more than 1.0 indicates significant cell death, and you should discard the slurry. ”
I never monitor pH, but never go past 2 weeks. If I do, I’ll maybe push it a few weeks more, but I take a portion and make a starter to ensure it’s still viable.
I find this a little confusing — is slurry the same as crudely washed yeast? I’ve seen the latter used after much longer than two weeks.
No rinsing/washing at all, just collecting a measured amount of truby/sloppy yeast and pitching that directly into another batch.
Matt, I have went past two weeks about 20 times. Just do it. Unless you don’t want to.
Nice Exbeeriment, I recall discussing repitching of slurry a year or so ago via email, and was quickly dismissed about this slipshod practice and that you were a devout purist when it came to yeast. Nice that you have widened your horizons 🙂 Love the part about accidentally swapping the beer lines and how strong the power of suggestion is.
Thanks!
wilser
I was blind and now I can see!!
You discovered what I’ve known for years! 😉
I see myself using this method much more in the future, especially for lagers!
When at home, do as the pro brewers do… And repitch!
This exbeeriment would be a bit stronger if you had accurate cell counts, as it’s possible and likely your two yeast sources had different counts, since you estimated the counts for both based on online calculators. There’s nothing wrong with that from a practical homebrew standpoint, but it does raise the concern that the difference is due to pitch rate rather than the state of the yeast.
Pro brewers came to mind for me too, but question on this — i’ve visited commercial breweries that claim to simply repitch right on the yeast cake. What procedures are typically done to (1) clean trub that would be included over and over again, and (2) have any clue about cell count?
Personally, I dump half the cake out and then rack onto, this keeps the trub line reasonable in my experiences.
Seems like a solid simple plan to me.
Nice! Have you done an xBmt on sloshing wort vs using an expensive o2 wand to aerate? Have read so many conflicting theories, am curious to see how much of a difference there really is in the end product if you’re pitching a healthy aerate starter.
It’s on the list!
Hmmmm. I’ve recently started taking my immersion chiller and jouncing it up and down – my theory is more surface area contact with the chiller/wort with a byproduct of oxygenation. Furthermore, after I take my gravity reading on my cooled wort, I pitch the yeast right into my kettle and then let it flow into the carboy from there. While the transfer is taking place, I like to slosh the wort around in the kettle adding even more aeration. I’ve had solid yeast activity within 4-8 hours this way.
One thing I would like to see you add when you do clarity comparison is to place the beers in front of a white background with some writing or image directly behind the beer. That way we can easily see the difference in clarity and get a sense of the color. Otherwise I love reading your experiments!
Oddly enough I performed a similar xBmt this weekend with two batches of Lemon Drop Saison. 1 batch was pitched with a slurry of Belle Saison collected from a previous saison two weeks ago and stored in the fridge. The other was pitched with a re-hydrated Belle Saison yeast I purchased over the weekend. The big thing I noticed was the slurry took about 16-18 hours to begin active fermentation. The rehydrated yeast took only about 12 hours. I think they contained roughly equivalent cell counts but I’m not sure since I didn’t attempt to quantify the slurry. I’ll be adding in some simple syrup in a day or two to both batches to dry them out and see if they still act different.
I could take a little more time when it comes to taking pics of the finished beers. Good call.
I have been on a WLP 029 kick myself.
I’ve brewed a couple of batches from overgrown starter pitches, most recently a kolsch. On that brewday, I had issues which caused me to rack most of the trub (including hops, hot- and cold- break) into my 6.5 gal carboy, which seemed excessive. I allowed that to settle for an hour or so before pitching, then racked the clear wort to another fermenter before pitching.
At the end of the fermentation, the yeast slurry appeared to be exceptionally clean, and there was so much of it, that i decided to brew a few small test batches pitched with the slurry. Active fermentation started within 4-6 hours, and the airlock operated like clockwork for 2 days before the krausen dropped. It is now day 3 it looks like fermentation is just about complete.
Totally non-scientific, but at least this experience suggests that the slurry yeast is ready to go. I’ll have to reserve judgement for a couple more weeks until I can taste the results, but nothing leads me to believe this will be less than a stellar fermentation.
And for the future (maybe later this week), I still have about 1/2 pint of slurry in the fridge to try in something else. Just need to decide on a recipe…
I assume that your slurry would have had some gelatin content from the previous batch? I wonder how this might affect either the fermentation itself, or the resulting clarity…
It did and doesn’t seem to have had a negative impact at all.
Any amounts of gelatin will already be fully gelled and will just sink. Following on from Truby/non-Truby as well it follows that there is no real issue to be had in transferring trub/hops/break from one fermentation to the next.
Me I’ve also never understood the mantra of pitching only from lighter beer to darker beer. Any dark beer which gets carried across is going to be so far diluted that you won’t see any impact in the final beer.
Great writeup…… again. I do both methods…… I harvest off of my starters, generally, if I am going to brew a higher alcohol beer or a beer I know is going to be loaded with hops. I harvest slurry in mason jars off of lighter beers, low hopped beers, etc. (Scottish 70, blonde ales, helles, etc).
I wonder if there is any issue with harvesting a “sloppy slurry” off of a heavily hopped, dry hopped beer???
I wonder if there is a difference between a mason jar of slurry yeast that has sat in my fridge for 2-3-4 months vs. one that is 2-4 weeks old?
I often harvest slurry from my fermenters (SS brew buckets or Bottling buckets) via the spigots after transfer to kegs. I leave a bit of beer behind, swirl it all up, let it settle for a few minutes which drops some of the heavier particles out, and then take sanitized mason jars out of star san and fill them about 2/3 full.
I have some 1-2 month old slurry in my fridge already…… I might have to make a point of allowing it to become 3-4 month old slurry and do a side-by-side with a brand new starter…….
Thanks for your great experiments!
Love your reference to “drift” and Hardy/Weinberg. The science geek in me loves this site. Thank you.
Cheers!
Good stuff man. Insightful, informative and entertaining as always. Cheers!
Great experiment. One note — I just bottled a Christmas Ale. I reused the yeast but before pitching I washed it well, because a noticable amount of the spices, orange extract, and vanilla definitely stayed behind in the trub. That’s one limited case where I’d say you don’t want to just pitch on the sludge. It’s probably also true for something with a lot of peated malt. But those are obviously fairly rare exceptions to what you’ve done here.
I haven’t formally experimented with pitching yeast from a slurry that contains spices and/or other flavorings, so until then, I think I’d agree that it may be best to either toss it or rinse it.
I over build my yeast starter now because it is definitely easier and really I don’t feel like messing with it when I’ve just kegged a beer. But…. what about collecting yeast from the kraussen?
Excellent timing with this xBmt. To follow up on Nate’s comment, I recently repitched two different unwashed slurries into two different beers one week after harvesting. I removed the slurries from the refrigerator at least two hours before pitching each time, bringing them up to room temperature to avoid the temperature shock. Both beers had lag times of 24 hours, which I admit made me a bit nervous. I usually pitch clean (room temp) starters made from a new vial or rinsed yeast cake and have lag times anywhere from 6-12 hours. Both beers are still in their fermentors so it’s too soon to tell if there are any noticeable differences. If there are none over several more batches (and unless it’s confirmed that the trehalose depletion idea is a thing) I’ll probably continue to used unwashed slurries in this manner because it’s just easier.
I tested my suggestion!
My recent experience was to pitch slurry that was unwashed, cold from 24 hours in the fridge to separate the beer, into wort.
I had never seen a krausen develop so fast. It was a thing to behold.
I just pitched a cold slurry today, already seeing signs of activity a couple hours on
I have used unwashed yeast slurry several times, and I have not experienced any negative flavors from doing so. Will continue to do so until something happens to change my mind on that
Has anyone tried an oxygen infused wort using old slurry? Maybe that kickstart would help.
Okay, using a jar of two month old WLP029 slurry in (m)Oktoberfest tomorrow. Will warm to room temp during boil. (I kept a jar of San Diego from last weekend for a future brew.). If I like the results I’ll keep doing this.
Please report back! If it were me, I’d be inclined to take the yeast out of the fridge the night before.
Yes, wish I would have, it took about 60 (nail biting) hours to get going but this morning it’s starting to bubble away. Next time I would feed it a little wort first to wake it up and make sure I see activity before pitching.
Or you can pitch it cold so it warms up in the delicious wort and does not have to deplete its energy stores. 🙂
I’ve used sloppy slurry many times and always let it warm up a couple hrs. It usually starts foaming and I have lag times of 5-6 hrs. I love this method and have used slurry months old.
I’ve yet to do this but certainly plan to in the future. Cheers!
On our pilot system at the brewery I work at, we brew 1/2bbl batches into buckets or carboys. We regularly knockout fresh wort on to a full yeast cake that beer has been recently removed from via kegging.
Any issues with pressure buildup while in cold storage? I have a couple mason jars of slurry that are about a month old in my fridge and noticed one jar had “leaked” a little beer from the seal. I untwisted the lids a tad to see what had built up, and both had a fair amount of pressure to release. Any experience with this from other sloppy slurry users?
I don’t crank the lid on and haven’t had an issue.
Just a thought, could you just bottle (and cap) the slurry instead of using a mason jar? I’m going to be bottling anyway so cleaning an extra bottle or two won’t be an issue.
Indeed!
I have been using beer bottles for about 2 years now. They are easier to open than a Mason jar, more uniform in size, and hold more pressure. Typically, I don’t harvest from a carboy, I build extra on my starters.
new to brewing and on a budget, i used one packet of nottingham on four 5 litre batches, and re-used each one for four more, so 40 litres! And i still have all 4 of the yeast slurry in the fridge.