Pitch It, Don't Toss It! Using Yeast That's Past It's Prime

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It happens, maybe you found a pack of yeast in the back of your fridge from last summer you forgot about, or you took a break for a while and still had yeast on hand before you stopped brewing, maybe you got your ingredients from a homebrew shop that doesn't check dates. However it happened you have found yourself staring at an expired pack of yeast thinking, "can I use this?".
On a recent trip to the LHBS I was presented with the opportunity to dig through the expired yeast & see if there was anything I would like to try & revive. I picked out several different tubes of varying age & took them home to see what I could do with them. I researched as best I could on using expired yeast and came up with the following procedures that have now worked for me on several batches using yeast well past it's best by date.
For this article I will be attempting to revive one of the older vials I chose, a vial of WLP566 Belgian Saison II that expired November of 2013(a bit more than a year ago).
hbt-kyle-1-1570.jpg

To begin you will want to make a small, weak starter wort with a gravity of about 1.020 this can be achieved using 500ml of water & about 27g of DME. You want to make the wort weak to make things easy on the few remaining yeast cells you have to work with, too much alcohol in the fermented starter is not good for the yeast especially in its weakened state. It is important to make sure that the yeast has all the nutrients it needs to grow additional healthy cells to prepare for fermentation, so I would suggest adding a pinch of yeast nutrient to the starter to provide it with the nutrition it needs.
Allow the starter to ferment for a few days, don't be surprised if it takes longer than normal for signs of fermentation to appear, or if signs aren't very noticeable this is normal. Mine took off within the first 2 days, signs of fermentation were weak, however you can see co2 escaping, and some bubbles forming around the edge of the flask.
After the initial fermentation of your starter has subsided, you can chill it for about 24 hours to allow the yeast to flocculate to the bottom of the flask. Decant the liquid saving the yeast cake at the bottom. Allow your yeast to warm up to fermenting temps while you make a new starter wort.
In a separate pot prepare another small, weak starter wort in the same way as the first this time, but lets make a 1000ml starter 54 grams of DME, and a pinch of yeast nutrient for a gravity of about 1.020. Chill your starter wort in an ice bath & add it to your flask with the yeast slurry in the bottom, recover the flask & allow it to ferment. Signs of fermentation may still be weak, but should start a bit sooner than they did the first time. After signs of fermentation have subsided, (probably 2 days or so) you can once again cold crash your starter to flocculate all of your yeast to the bottom of the flask.
Once more after 24hrs or so, you can decant the liquid from the starter & allow the yeast to warm up while you make a new starter wort. This time our yeast should be a bit more viable so I am going to do a normal 1000ml starter wort with 100 grams of DME, for a gravity of about 1.037, I am also going to add a pinch of yeast nutrient again. Fermentation should be a bit more vigorous this time around, mine showed a krausen for the first time.
hbt-kyle-2-1571.jpg

At this point your yeast slurry should be quite viable, you can go ahead and use a standard pitching calculator to figure the amount of slurry you are going to need to ferment your batch of beer, and the amount of subsequent starters you may need to make to reach your cell count. All starters from this point forward should be of standard starter wort strength (between 1.030-1.040 SG)
I stepped this one up enough to pitch into a 1.072 OG beer and my "expired" yeast got it all the way down to 1.007 FG that's roughly 90% apparent attenuation!
hbt-kyle-3-1572.jpg

So, if you come across some expired yeast in your fridge at home, or on discount at the LHBS , don't be afraid to use it, It can still make great beer.
After this experiment & writing this article I was curious if the same process would work for expired dry yeast, though I have not conducted this experiment with dry yeast I did email two of the largest producers of dry brewing yeast Lallemand, & Fermentis asking if this would work. I was Informed that, yes you can, rebuild cell count using starters with dry yeast as well. Although, with the time & DME involved in making all these starters, & the price of dry yeast I would still probably say it is best to just replace expired dry yeast.
Cheers
hbt-kyle-3-1572.jpg
 

guitarpat

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I have not tried to make a starter with expired yeast, but I have pitched slurry that had been in my fridge for 6 months.
 

broadbill

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@guitarpat: I used to directly pitch slurry, until one batch where the yeast didn't take off and it ended up infected. It was the only beer I had to dump in my 15+ years of homebrewing.
My reading/research indicates that slurries are probably good for 1-2 weeks after harvest. After that viability drops off, concomittant with depletion of yeast glycogen reserves. At the 4 week mark it can be 50% or lower.
A culture that contains 50% dead yeast isn't the type of thing you want to put into your wort if you want to get a quality product on the other end, IMO.
 

itsme_timd

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Good timing on this article as I just picked up some expired vials at my LHBS and was going to try stepping them up. Thanks for the info!
 

finsfan

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@broadbill - Whats the difference between washed, ranched, or yeast slurry viability compared to a new vial of yeast? IMO, the viability will all drop off at about the same rate. I personally ranch yeast and pitch clean after a starter, and have never had an issue with keeping yeast in the fridge for 9+ months. There isnt much viable yeast left after a long period of time obviously, but that just means another step up on the starter. Even if you were to pitch a slurry without building it on a starter, I dont see how that could possibly cause infection. It might cause off flavors due to stressed yeast, but IMO your infection was due to your sanitation, not the dead yeast.
Great article BTW!
 

Fionnbharr

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Not to nitpick, but check with your editor (the person, not the WordProcessor) regarding spelling.
A 'Vial' is a small container used to hold (usually) a liquid. Some yeast producers (famously, White Labs) sell yeast in them.
Your spelling of 'vial' is most vile.
 

brewprint

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@broadbill I've done it with slurry months old and never an issue.
 

broadbill

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@finsfan
To clarify, the batch I referenced as getting infected did so because the wort sat for 3-4 days without any active fermentation. I would challenge you to let a wort sit unfermented for 3-4 days and see how your santization procedure holds up! The take-away here was that pitching a culture with low viability results in a long lag time and increased opportunity for infection.
As to your question about differences between forms of harvested yeast...yes there are differences. Harvested slurry have been through the proverbial "ringer":kept very active metabolically, and exposed to high alcohol % as well as various hop compounds. Additionally, they are exposed to large hydrostatic pressures after settling out and sitting under many gallons of beer, often for weeks at a time.
My opinion is that harvested slurry from the bottom of a fermenter is one of the WORST places to get cells for subsequent fermentation or repropagation (with some exceptions). The reason it works as well as it does is because of the sheer number of cells you can harvest.
 

broadbill

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Kyle: some questions/comments-
Do you have a reference for using the lower OG starters to step up the old vials? This is the first time I heard about it and I could see how low OG worts could stress yeast similarly to starters with high OG.
How many times did you attempt this? Your writeup suggests that this was done only once and I would caution that the method may not work with other strains or older vials.
Lastly, that 90% attenuation indicates to me that the wort was overpitched and not necessarily that your process was solid. Obviously you must have done something right as you didn't have underattenuation. However, overattenuation isn't good either is many cases (makes beers light bodied, but it is a desired trait here in your Saison).
Anecdotally, I have seen overattenuation when I pitched harvested slurry, which is another reason I got away from using them. Pitching appropriately-sized and healthy starters have worked much better for me.
 

mkyl428

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@broadbill I do not have one specifically regarding expired yeast it comes from the idea that the yeast will be in a weakened state and at a low cell count and you can build a cell count quicker with a weaker wort also there is less risk of mutation.
I can give you references on that if you like.
https://www.homebrewersassociation.org/attachments/0000/1235/MAzym07_YeastStarter.pdf
"When making starter wort, keep the starting
gravity between 1.020 and 1.040 (510 P).You do not want to make a high gravity starter to grow yeast."
http://gluttoncooking.blogspot.com/2012/03/two-hearted-ale-how-to-culture-yeast.html
"However, we need to rouse the sleepy and sickly yeast. So make up 100-200mL of wort at half strength (1.020),"
http://www.maltosefalcons.com/tech/yeast-propagation-and-maintenance-principles-and-practices
"Lower gravity starters (O.G. = 1.020) are commonly used by homebrewers and routinely produce higher concentrations of yeast but do not perform well when pitched into normal brewing worts"
from an email i had with fermentis
"The way in which we propagate is by dosing our propagation vessel with sugar and nutrient, keeping the sugar concentration around 0.5%. When yeast are in a sugar solution this low, there is no alcoholic fermentation but rather only bio mass growth. With our propagation happening this way, we can assure that the yeast has never been exposed to high osmotic pressure from high sugar concentrations and has not been exposed to alcohol, which at levels can damage the cell wall/membrane."
http://www.franklinbrew.org/wp/?page_id=124
"The composition of the wort determines yeast growth and fermentation performance. The presenter believes that the closer the starter composition is to the wort being fermented, the better. Yeast growth in OG 1.020 wort results in higher yeast masses, but is not recommended (this is used by the yeast companies)."
You will notice that many of these however do not recommend pitching from a low gravity starter that's why the last step is a standard strength starter to acclimate your now healthy starter.I'm pretty sure there are some YouTube videos I've seen addressing this too although for the life of me right now I can't remember which ones sorry...
I have done this in 5+ times now with success on all batches so far. sucsess with WLP090, WLP400, 2 WLP566, WLP002,& WLP515. I don't have the experation date in front of me for all of the vials, however they were all at least 6+ months expired except the WLP400 it wasn't quite as old.
The article was the 3rd time I tried this and I chose the oldest one I had when I wrote the article.
As for attenuation maybe I should have mentioned in the article but as you said it is desired in a Saison, and I mashed low around 147F for this particular beer it was an American IPA I fermented with Saison yeast as an experiment.(turned out amazing by the way!) Also many people report this kind of attenuation with this strain.
Cheers
-Kyle
 

FredTheNuke

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But do you pitch the entire cold crashed slurry (including the old/dead/weak/junk cells?
I recommend that on that 3rd starter where you see a krausen you pour the liquid ONLY into a 4th starter of 1.040 wort leaving the gunk on the bottom behind. Now you have isolated good cells for your future drinkable fermentation.
 

wildactbrewer

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Not to change the subject, but could the same methodology be used to cultivate a pitchable population from the dregs of a commercial beer? Or is that a different process all together?
 

mkyl428

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@wildactbrewer excellent question! Yes it can, just make sure you are sanitary in your process & don't forget to sanitize the beer bottle you are harvesting dregs from.
 

WoodlandBrew

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Nice write up! I appreciate the references you left in the comments. It's a lot of work to do these types of experiment. Thank you for taking the time to write up and share your findings. It makes me want to try some similar experiments. I would probably do it in a similar fashion as FredTheNuke suggests, and include viability at each step and cell density daily.
 

Fionnbharr

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@Holybarfly
Yeah, but I love me a bad pun. Vile yeast makes terrible beer. Vial yeast is good stuff.
Now, back to my cookbook... Wondering why my chicken is so fowl-tasting.
 

BigPicture

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When using a washed yeast that I had in the fridge for over 1 year, I had more krausen in my starter then I normally get with a brand new vial. I'm sure I had more than enough healthy yeasties.
 

stonebrewer

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For growing yeast, I never use DME for starters anymore. It is so easy to dump extra water into the mash tun once drained and get perfect wort for starters!! I usually get a gallon of 1.030-1.040 wort that I stick in the fridge until the next brew. Good write up on yet another way to save a little cash and still brew great beer. Cheers!
 

broadbill

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@stonebrewer...you left out the part where you boil those runnings so the loads of lacto on the grain don't get carried forward into your starter, right? right?
If you aren't boiling, I don't get how you aren't getting some sort of infection with that process.
 

azscoob

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My competition winning mild was made using an extremely old packet of notty, it was several years old when I pitched it into the wort. Granted my beer had a starting gravity around what a typical starter would be, it took a few days to get rolling but it turned out fantastic!
 

Wolfbayte

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@wildactbrewer
https://www.homebrewtalk.com/Harvesting-Yeast-from-commercial-bottles.html
 

BrewingSailor

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@Schreiner
+1 on the time commitment vs. value derived comment.
I have not invested the time in education or $$ in equipment to be set up to KNOW the health and count of yeast that is harvested or reconstituted. I have come to trust the manufacturers and rules of thumb for calculating new yeast viability (Mr. Malty). I brew once or twice a month on average, and this really isn't often enough to justify it for the potential cost savings. My experience has taught me that pitching the right amount of healthy yeast is so important that I am not going to risk ruining a batch by guessing with the yeast (well, I won't do it any more).
However, more power to everyone who chooses to do this to save money, or for whatever reasons you do this! If you like the beer you make, that's all that really matters. Thanks for all the experimental work and sharing your results! This will continue to be a topic of interest for me.
 

benbradford

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I believe this write up would be more appropriate for harvesting yeast from the leftover dregs of a beer to capture an obscure yeast strain. Or perhaps, if the yeast strain was one that is not currently available for sale.
When you factor the cost of the dme, even if only $2-3, plus the time, this doesn't seem appropriate for ending up with a $7 vial of saison yeast.
I place a large value on experimentation and improvisation, but, I also feel that the conflicting reports on yeast management and practices expounded on this forum are not accurate. After that one batch in five just doesn't match up to the previous, you have to wonder what is different. Yeast is often the answer.
I recommend spending the time reading a book about yeast and considering the practices implemented by the leading breweries and modeling your yeast management after what you found to be based on fact, and the recommended care of yeast.
 

andrewmaixner

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@MrSnrub Mostly because the English language often doesn't follow its own rules. How many nouns/pronouns can you think of where the possessive form lacks the apostrophe? It's not a huge deal, and it's pretty easy to figure out the meaning from its context :)
 

sakeyfour

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Excellent timing on this article. A friend just asked me to brew a kit they bought and never had the time to brew. It was over a year old. I had some hops to add to the older ones, but not the yeast. Followed the process and have very vigorous fermentation after 8 hours. Thanks
 

guitarpat

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@broadbill Oh, I wasn't suggesting saving it that long. I was just saying I did do it once and it worked. I usually don't hold it for more than two weeks :)
 

SeraW

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Found this article using the Search function. Came in handy as I revived a friend's harvest of White Labs American Farmhouse Ale yeast that was harvested an unknown number of months ago and stored in the back of my fridge that occasionally freezes back there. Starter activity is now very strong and I'm ready to brew tomorrow.
 
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