Yeast Harvesting

When I initially started tinkering with the idea of harvesting yeast from starters, I was unable to find references to anyone else using a similar method. Since I wrote about it, I’ve heard from a number of folks who had been using a similar process, hence I take no credit for developing this method and appreciate all the feedback I’ve received.

Here is the most updated version of how I harvest yeast from starters.

STEP 1

Make your starter at least 24-36 hours before you plan to pitch, I’ve learned that older strains tend to take a bit more time than more recently harvested yeast, so plan accordingly. Using a good yeast calculator, overbuild your starter by 100 billion cells. BrewUnited’s Overbuild Harvest function makes this so incredibly easy, you can even download a spreadsheet version. Usually, the extra amount will be less than or right about 1 liter.

04

STEP 2

After at least 24 hours on the stir plate (longer if shaken or using older yeast), you can harvest the yeast. Since I like to crash and decant, I always harvest my yeast the night before I brew. To do this, sanitize an appropriately sized Mason/Ball jar using whatever sanitizer you prefer, remove your flask of starter from the stir plate, secure the stir bar using a magnet, and fill the sanitized jar with the proper amount of slurry.

I usually give the flask a good swirl before transferring to ensure homogeneity. Loosely cover the jar with a sanitized lid and place it in the fridge for 24+ hours. This is also the point I’ll move my flask to the cold ferm chamber to crash overnight.

06

STEP 3

Place the jar in the fridge and pull it out a few hours before you make your next starter. That’s basically it!

Previously, I encouraged people to replace the beer on top of the yeast with pre-boiled and chilled water if they planned to store it for longer than a couple weeks. However, I’ve recently been made aware of some fairly convincing evidence suggesting this is both unnecessary and potentially harmful to the yeast. I started leaving the starter beer on top of the harvested cake and I’ve experienced no noticeably negative impact. For these reasons, I no longer plan to replace the beer with boiled water and recommend others follow suit.

After some time in the fridge, a nice layer of creamy yeast will be sitting at the bottom of the jar.

08

F.A.Q.

How many generations of yeast can be harvested before it goes bad?
I’ve only anecdotal evidence, so keep that in mind. At the writing of this article, I have two strains of yeast, WLP090 San Diego Super Yeast and WLP002 English Ale Yeast, both have been harvested 13 times. The 12th beer each fermented tasted great with no noticeable differences compared to the original vial. I’ve used this method successfully with ale, hybrid, and lager strains.

What makes this method any better than rinsing (“washing”) yeast?
To start with, I personally think it is much easier and far less time consuming. 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. I also like that I’m only harvesting a single jar of yeast as opposed to multiple jars that would eventually end up in the trash.

How much yeast is actually being harvested using this method?
I don’t know. I wish I knew, but I’ve yet to find anyone with the know-how to do an official count. As I mentioned before, I’ve been assuming 100 billion cells, though I fully accept this number is likely way off. Still, it has worked great for me.

If you have any more questions or comments, please do not hesitate to ask. Cheers!

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343 thoughts on “Yeast Harvesting”

      1. Dave Mitchell

        I’ve been top cropping my yeast as of late. The last batch I cropped is off a 1.075 OG beer. Have you ever done an experiment on storing yeast at a higher ABV than 1.040 to see if there is an adverse effect on beer?

      2. Can you please tell me the reason for loosely covering the jar with the lid for 24 hours prior to tightening it?

      3. Marshall Schott

        Safety measure— allows gas release if fermentation happens to continue.

  1. How tightly do you monitor your temperature with your starters? Do you do them in a temp controlled ferment fridge?

    1. Marshall Schott

      I pitch yeast when my starters are ~73F and let them spin at room temp, I’ve measured with a IR thermometer the fermenting beer to get as warm as 80F, never been an issue.

  2. ChosenOneTim Leek

    I brew every 3-4 weeks. Once I transfer to secondary, and save the slurry at the bottom of primary vessel, how long do I have until I need to re-pitch into a new batch? Will it save for 4 weeks and at what temp does it need to be at?

      1. ChosenOneTim Leek

        I saved the slurry from my last batch brewed on 04/08/2017 and its in a tin foil covered mason jar in my keezer currently at 38 degrees F. The yeast has settled to the bottom and there is a 2 inch layer of brew sitting on the top. Should I remove the layer of brew from the top and also, should I “feed” it with some new work (I can whip up some wort using DME)?

      2. Bel Air Brewing

        I have used a yeast slurry that was harvested and sat in cold storage for 5 months. It was just fine.

  3. I may just be really dumb, which is a distinct possibility, but I can’t seem to figure out what size mason jar to use for storing the yeast harvest for next time. How much liquid am I supposed to take out of the flask and store for the next round?

    1. Marshall Schott

      Lately, I’ve been overbuilding by 1 quart then pouring 1 quart of the starter into a 1 quart jar. Been working good.

      1. Thanks for the response. Just for clarification. If I plugged in the numbers in the calculator listed above (the yeast starter calculator) if I wanted to overbuild by 100 billion cells with the SG set at 1.055 I would use 1.5 liters of water and 151 grams of DME. Then I’d let it go on the stir plate for at least 24 hours. After that I would pour off 1 liter (a quart is basically a liter) and add another liter to the starter. Let it go for 24 more hours, cold crash that and pitch the slurry?

  4. Regarding lager strains, have you ever had an issue storing lager yeast in the fridge? I’ve read that you are supposed to store lager strains colder than 40°, I’m curious if you’ve ever had an issue or if you treat lager strain’s differently when storing?

  5. Maybe I missed something but isn’t estimating the yeast cells as simple as using a yeast calculator to determine the cell count of your starter, figuring out what percentage the jar you’re going to pour off into is compared to your Yeast Starter, and then multiplying the cell count by that percentage?

    For example, if I have 500 billion cells in a 2000 milliliter homogenized starter and I plan on pouring off 400 milliliters, is it safe to assume I have harvested 100 billion cells?

  6. I have been using this method for maintaining a supply of Bell’s yeast initially harvested from a case of Oberon. Only a couple brews in but so far so good and I haven’t needed to buy yeast since I started. Thanks, Marshall!

  7. I have done this method a few times, I am wondering if I am over building or not. A dry packet of yeast has 200 BB cells, so do I over build by 100 BB or 200 BB? I assumed we are basically doubling the yeast (dry yeast = 200 BB) then splitting for next time.

  8. One thing I’ve never completely understood when making a starter: what state is the fermentation ideally going to be in when I harvest yeast and/or pitch my starter?

    In a perfect world, would I wait for the fermentation process to complete, the krausen to fall, and then pitch/harvest? Or is the goal to have yeast that are actively in the process of fermenting that starter wort, and harvest/pitch them in this active state?

    Thanks!

  9. Once yeast has fallen to bottom which shouldn’t take more than 24-36 hours if you OG from the starter wasn’t too high. On brew day, I usually cold crash my 5 liter erlenmeyer flask early in the morning, let white layer of yeast cells flocculate to the bottom, carefully decant 75% of the beer leaving behind only 25% or so, then I leave it set in an area that’s around 70 degrees. Usually, the starter is roughly that temp by the time I’m done brewing. Just make sure your batch of wort is within 10 degrees F of the starter before you pitch – I shoot for 70 degrees. Give the flask a good swirling around to break up any yeast clumps (if pitching in multiple vessels) and then pitch. I do 20 gallon batches using 4 each 5 gallon carboys so The swirling around is important so I break up any yeast clumps so I get an even amount of pitch per carboy. This probably doesn’t matter too much if you are pitching into one vessel. Lastly, its not imperative to wait until the starter has fully attenuated before pitching but based on my research, if you wait until the starter fully attenuates, you should have the maximum amount of cells created by your starter.

    1. Thanks for the quick reply.

      So if the goal is to let the yeast fully ferment (and then potentially cold crash to drop it out of suspension for decanting), can I assume there is no big rush to pitch the yeast immediately after making the starter?

      In other words, once I’ve followed the procedure described by Marshall and made an overbuilt starter, harvested a portion of it, cold crashed the rest, it shouldn’t matter if I cold crash for a day or a week before pitching into my fermenter, right? Most of the yeast will have dropped out of suspension and won’t be actively fermenting at that point anyways, right?

      1. I always thought one of the goals of making a starter (in addition to building up cell count) was to get your yeast active and pitch them while they are still actively fermenting in your starter to minimize the lag after pitching. This procedure doesn’t seem to aim for that goal, but I just want to be sure I’m not missing something.

        One of the challenges of yeast starters for me is timing it so that my starter is at the right point to be pitched direct from the stir plate. If I can do my starter further in advance (a couple days, a week maybe) and then just grab the flask out of the fridge on brew day and let it warm up before pitching, that would make my life a lot easier.

      2. I would pitch it into wort within the shortest time possible, while still somewhat active or shortly after (same day). Yeast viability is best during this time. When you let yeast sit, even at correct temperature, over time, yeast cells die, and then you would probably need to make a completely new starter (step) to make your yeast happy again and bump up the cell count. There is tons of research on the subject and I’ve even had some homebrew buddies claim that yeast cells become “stressed out” when there are no sugars for them to eat, but I don’t know enough to know whether that is true or not and certainly no evidence in my brews. I recently bought a smack pack of Wyeast 1056 (100 Billion cells) that had a date of July 31st stamped on it. Using the Brewers Friend calculator, when I pitched it into my starter a few days ago, The viability was at 68% which meant the calculator estimated I really only had 68 billion cells (much lower than the 100 printed on the pouch). When you go to your LBS, make sure you pull your smack packs from the back of the cooler and check the date. The shop employees may get pissed cause you are not using up their older inventory, but its the smart thing to do if you want maximum yeast cell count.But to answer your question: Id pitch the yeast right away and not store it unless you plan on making a completely new starter after a week just before you brew and pitch into your batch.

  10. Just pitched yeast that was harvested from a starter in late May. Built a 1 L starter the stepped up to 2 L. Put the yeast under the microscope with stain and very few dead cells. Pitched it a 9 PM and 9 hours later had a strong fermentation going. About 10 generations in on this yeast and it still seems to be working fine.

    1. I’m reading a book written by the founder of White Labs, Chris White, called “Yeast: The Practical Guide to Beer Fermentation”. On page 138, in the “Making a Starter” section, Chris says some brewers wait until the yeast consume all the starter wort sugars and settle out of solution (drop), decant, then pitch just the yeast into their batch of beer. He says this is advantageous when doing larger starters which he classifies as 5% or greater of the final beer volume (ie: 4 liter or more starter for 20 gallons of beer). He highly recommends settling, decanting, and pitching only yeast so as to not pitch in the beer from the starter. However, he says other brewers like to pitch their starter as soon as the growth phase is NEARLY complete and the yeast are still at the height of activity so they do not have to come up from the dormant stage again, thus ensuring quicker yeast activity in the batch of beer. However, he says if you pitch this way (during high kraeusen), its very important that the starter and batch be within 5-10 degrees F of each other so as to not stun the cells which can affect attenuation, flocculation, and increase hydrogen sulfide production affecting the flavor of your beer. Lastly, if you choose the first method and wait til the yeast drops, he says waiting an additional 12 hours allows the yeast cells to rebuild their glycogen reserves resulting in better fermentation. He doesn’t really mention preferring one over the other but storing yeast and pitching without doing a new starter seems fine as long as the yeast is healthy and contains the amount of living cells needed to ferment the beer. It just make take longer to see activity since you are pitching the yeast from a dormant state.

      1. Tim, thanks a lot for doing the digging and summarizing your findings so clearly! Everything you found makes perfect sense, and settles a bunch of open questions I was struggling to find answers for.

        Much appreciated!

    1. Yes I do, however, I’m not sure how much it actually helps. If you are pitching the right amount of yeast, I doubt it would be an issue if you didn’t. I only use it because its so cheap and I figure why not….

  11. Any idea on how long can the harvested yeast can last? I have a jar of harvested yeast that is 2 months old, which I collected using this method, but have not had time to brew, and am wondering if it is still viable.
    Thanks,
    Connor

    1. I’ve propagated harvested yeast that was 4 months old without issue, though my general rule of thumb is to toss it when the entire cake has turned brown. If it’s just a small layer on the top of the yeast, I’d use it!

    2. I think this topic is very subjective. Most material I’ve read recommends using harvested yeast within a few weeks of collection. But Ive also heard of people using it months later. With DME being so cheap, I’d recommend giving it a whirl. Make a starter using DME, cool it off, and let your harvested yeast warm up to within 5-10 degrees of the starter and pitch (maybe 72 to 74 degrees). Let the yeast do its work and once fermentation subsides and settles to the bottom, try decanting the beer off the top, pouring it into a cup, and tasting it. See if you can detect any off-flavors. If not, you should be OK stepping up the starter for brew day. If you detect any strange or foul flavors, I wouldn’t risk it. In a perfect world, one would harvest the yeast slurry from batch A and repitch immediately into batch B (brewery style). But most homebrewers dont overlap their batches like that so storage is a must. Good luck!!!

      1. One thing I forgot to mention: dead yeast cells tend to fall to the bottom of the fermentation vessel first while healthy cells remain in suspension during fermentation. Therefore, when you harvest your yeast, its best to recover the top 2/3rds of the yeast layer and discard the bottom 1/3. This way, you aren’t collecting/repitching dead cells in your next batch, which will affect flavor. Dead yeast cells go through a process called autolysis where the yeast cells’ enzymes begin eating the yeast cell itself. This produces “yeast bite” which will really screw up a good beer. Therefore, you want to prevent repitching dead cells into your next batch so its wise to discard the lower layer of yeast during collection.

  12. When I buy new yeast, I make a 4-5 liter starter, put in sanitized jars, mark the date and type of yeast and cold crash in the fridge. I’ve used these just fine up to 2 months with absolutely no problem. After 2 months, depending on my beer, I’ll make a stepped up starter to use. One pack of yeast usually gets me 6-8 beers before I start over.
    Only once did I open a jar, 4 months old that I felt it smelled off. I tasted it and it wasn’t awful, just not right so I ditched. Never had any infections or off flavors. It just works for me.
    Find what works for you and stick with it!

    1. Agreed…..you can usually tell from the taste when something isn’t right. Many brew pubs use the “tasting” method to determine when their yeast has been used too many times because they dont have the money or time to buy microscopes and other equipment to examine yeast cells (lab setup). Often times, a general beer consumer cannot fully distinguish when a yeast has been used too many times. As homebrewers, we tend to have a better taste for off flavors that we learn over time through experience. So as you mentioned, its best (and fairly inexpensive) to just taste it and see.

      1. AFTER you decant the spent beer from the jar of yeast. I certainly wouldn’t advise putting your mouth directly into the jar that contains your yeast unless you are looking for some funk in your next brew.

  13. Can anyone tell me how fast the yeast that is harvested and kept in a fridge dies? I’m trying to calculate viability in order to make a new starter from the harvested yeast. Is it approximately the same as packaged yeast?

    1. Marshall Schott

      I’ve used yeast that was harvested about 3 months prior and it has worked fine. Not sure that answers your question, but I just assume similar viability as packaged yeast.

      1. Did you have to feed it DME or anything over that 3 months? I know when my wife does a sourdough starter she feeds every 12 hours sometimes.

      2. Nope, just took it out of the fridge, decanted the supernatant, and pitched into a starter.

      3. I boil all my mason jars and lids for 10 minutes and then fill the jars with the boiled water, seal, cool and refrigerate so all I have to do when I’m ready to add yeast is open and empty the water and fill with yeast.

      4. @Paul. I do a similar thing but fill my jars with Starsan. I always seem to have some mixed Starsan around at bottling.

  14. I’m a slurry harvester and have pitched year old mason jars without issue. I pitch it all and don’t worry about the dead yeast. I have yet to notice autolysis but perhaps I’m not too aware of what that tastes like. I know autolysis is a key part to making fine champagnes so perhaps it is a bit of a boogieman because I don’t notice offensive tastes in champagne. Also dead yeast is a key component in the yeast nutrient we add. The only issue I have had is with London Ale III which after 3 generations lost some of its character. I have been top cropping this.

  15. Long time reader, first time questioner 🙂

    About sanitation: You mention sanitizing your jar that you split the slurry into, which of course makes sense. I’ve recently been reading about making jars of starter wort ahead of time so that you don’t need to boil a fresh liter of wort every time you make a new starter, but conventional wisdom says you have to sterilize via pressure cooker @ 15 psi (to reach an internal temp of 250 degrees) to insure everything is sterile. If you’re splitting a starter batch into a sanitized jar and it stays in a fridge for, lets say, a month, how come there’s no similar concern for contamination?

    1. i follow the rule of thumb that if you are storing a liquid and can sterilize it, do so. if you have inly a surface, you can sterilize or sanitize.

  16. What type of flask are you using? I’m considering upping my flask from a 2L to a 5L so that I can potentially start harvesting this way. Do you boil the starter wort in the flask?

    1. I have a 3L and 5L and use each about 50/50 depending on the strain and how much I want to keep and over build. I boil for 12 minutes in my flask and use Fermcap S so that it doesn’t boil over. You only need a slight boil anyway, no need for a hard boil.

    2. I boil directly in the flask for only 4 or 5 minutes with no issues. Like Paul said, a couple drops of Fermcap or unflavored and unscented baby gas formula is a MUST when boiling in the flask. I find a 2 liter is good for vitality starters while 5 liter is better suited for harvesting.

      1. Where did you get your 5L flask from? I currently boil in my 2L Pyrex flask with a couple drops of Fermcap and haven’t had any issues. Just want to make sure I don’t get a horror story 5L knock off somehow that explodes while boiling on the stovetop.

      2. I used to boil in my 5L flask, but I’ve broken two of them now. I bought a dedicated sauce pan and just transfer to a sanitized flask now. Seems to work fine.

  17. Marcos Junior

    What about top cropping? Hasn’t someone of you guys top cropping? I’m just thinking to do it right now the first time, but I am afraid on oxidation..because it is an IPA. On the other hand, bottom cropping in this case I will find very much hops in the slurry.

  18. How do you determine the amount of slurry to pull from the overbuilt starter? Assuming you need 200B cells and you build up to 300B cells, will you just take 1/3 of the slurry and transfer that to a small mason jar?

    1. I use dad’s calculator on brewers united, which I will set to overbuild by 200MM, it will give you the slurry split for the pitch and the over pitch. For example 3L starter, 2L pitch and 1L harvest.

  19. atupid question here. After you harvest from your starter, do you then pitch the flask into your new wort right away? or is there some time between each step.

  20. Hi Marshall,

    First up – thanks for writing this up. It’s a great resource, both this and the Yeast Starter Method article. You’ve inspired me – I’ve ordered a cheap stirplate and a 5L flash to give it a crack.

    I’ll be honest here – my main motivation is to save money. I brew once every 4-6 weeks, and generally fill two FVs at a time. With one pack of US-05 in each, that’s between $10 (if I buy online) to $17 (if I buy locally) for the yeast. I figure at that rate, I’ll make back the investment on the equipment in under a year. Plus I get to do sciency things!

    Keen to try and cultivate some different yeasts while I’m at it, including recovering some from bottle-conditioned commercial beers. But that’s more of a fun experiment vs anything else.

    At the time of publishing this you had mentioned that you had yeast that had been harvested 13 times, and was still going strong. Just curious as to how that’s going – did you eventually hit a ceiling when you had to dump the yeast and start again, or are you still going strong?

    You’re obviously doing this in a linear fashion – I’m wondering if there would be benefits to yeast longevity in running a couple of parallel streams? IE, build the first starter and split it into 2 x litre mason jars, and then alternate between them. You could then run, say, 12 generations on each one from new, getting 24 brews from a single original packet. Happy to admit that I may be overthinking this though.

    Again – thanks very much for writing this all up – it’s still very valuable years later.

    Cheers,
    Matt

  21. I had been previously following this procedure, but I stumbled on the “James bond” method, which is apparently old news, but so far has given me quicker starts within 12 to 24 hours, which it seems you guys normally hit that start time, but for some reason I haven’t been as lucky and sometime takes longer. I think it’s equivalent to the vitality method, just not sure the effects of stir vs shaken but o2 seems to be extremely important. So you might want to test out these other methods.

  22. I love this method but was thinking about one potential problem this morning…I have never tested the PH or the FG when I harvest, but if the PH isn’t yet below 4.6, it’s at risk for botulism if you put it in the fridge and stop fermentation activity. Best way to avoid this would be to leave the harvested jar at room temp a few days to finish up fermentation.

  23. I always assumed when using the yeast calculator to overbuild that the yeast you pull off for later then needed to be turned into another starter before you use it down the road. Then overbuild, save off more…etc. Are you all just pitching the saved off yeast right out of the canning jar as is?

    1. Johnny from the Block

      You can pitch the saved yeast directly for up to a month (just make sure you’ve saved enough for the correct pitch rate of the beer). After that you’re best off to re-do a starter. I’ve even saved enough to direct pitch the next batch I’m doing a month later AND still have 100b cells left over to save for the future.

      1. Johnny from the Block

        Just make sure you’re accounting for the yeast die-off as it sits in your fridge – it’s probably the same rate as the yeast calculators use for store-bought yeast packets.

  24. Johnny from the Block

    Marshall, you say you pull off a liter of the starter to save – is there any reason why I shouldn’t chill, decant off half the natant, reswirl the yeast into suspension, and then pull off half a liter in order to store it in smaller jars (save space in fridge)? This would end up with the same number of cells but half the beer on top of them. Thanks in advance

  25. exbeeriment suggestions: v old yeast that was harvested using your method vs new pack from manufacturer? (…. I have a couple of harvested starters that are about a year old that I am planning to use soon!)

    1. I just pitched a 6 month old harvest of A1, it was very sluggish. My humble recommendation would be to start the starter earlier, be prepared for second ramp up starter based on vitality.

  26. Mike Elderkin

    In order to more closely approximate 100 billion cell yeast harvest to store, why not just mix the finished starter well and take the fraction of volume in your starter that was required for your 100 billion cell overbuild. So say you needed 2.5 liter starter for your upcoming batch and you need 3 liters including the 100 billion cell overbuild, then you would mix up the starter well and quickly pour off .5 liters. I’m going to start using this technique instead of washing my yeast after fermentation. cheers!

  27. Ive used the same method harvesting some yeast from my starter, but just use a regular beer bottle and crown cap rather than mason jar, typically let starter go for 48hours so is fermented out

  28. jeff shoemaker

    Hey, peeps!
    I wonder tho, onceni have my harvestes yeast I am about to make a starter with, how do I use that with yeast calculators to make a good starter along with over building again to save more yeast for next time? Thank you!

    1. That should be pretty easy if you overbuilt your previous starter and harvested approximately 100 billion cells. I just siphon off most of starter liquid, then stir well and pour a calculated fraction of my built starter – ie if I built 800 billion cells, I pour off 1/8 volume of well stirred finished starter after siphoned liquid is removed. Now I essentially have a new 109 billion cells. Just enter this into yeast starter calculator with the date that you use this yeast to make your next starter. Couldn’t be much easier.

  29. Does anyone have a working link to the excel version of the calculator? The link on the site doesn’t work for me.

  30. This is really interesting reading! I have read through all the comments and have a question: if I recover the slurry from a 5-gal batch (that I made using MJ’s M44 in a 1l starter with 140g DME) that I have just transferred to a second FV to cold crash, how do I estimate how many billion cells I have likely harvested in the slurry? I’d like to store this yeast slurry and re-use but fear I have lost my datum on numbers of cells. Any help appreciatively received!

    1. I started with 2L, then a 3 to 5. If you make lagers, you’ll want a large one. I rarely use the 2L anymore.

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