How long does a yeast slurry remain viable?

[Happy Chappies]

Hi all,

For a while now I've been trying to save a few pennies and resources by reusing my yeast 2 or 3 times before pitching a fresh pack. That's been great so far, but has resulted in me brewing 2-3 of the same style before changing to the next style.

I'm wanting to change it up and maybe rotate 3 different yeasts, which means storing them for longer periods. While I've looked into yeast rinsing, I can't really be bothered with the faff involved and if a slurry would keep long enough would rather just do that.

In your experience, how long does a slurry last and remain respectably viable? And are there ways to improve long-term storage?

(and also, does champagne yeast store just as well as an beer yeast? I have a hard lemonade coming out of the FV this weekend and would like to store the yeast for a ginger beer down the track....)

 

Thanks.

[Otto Von Blotto]

Not sure about slurry from a fermenter but yeast harvested from starters I observed had a viability still up around 80% after two months, using a microscope and trypan blue staining of samples. I'd expect the slurry would lose viability a bit quicker than that simply because it contains more shit than yeast that comes from a starter, maybe 70% after two months but I've yet to test it. It's on the to do list though. 

If you leave it for months you may need to build it back up in a starter, but that also depends how much you take from the fermenter. If you take half to two thirds of the cake then you should be able to simply pitch it next time around as there would still be a good amount of viable cells in it.

I keep three strains in storage all the time and rotate them brewing a different style each batch. My harvest method is described in another thread, using starters rather than fermenter trub.

 Cheers

Kelsey 

[Happy Chappies]

Thanks Kelsey - that's encouraging to hear. I'm only pitching into 10l volumes, so it sounds like my rough plan of storing a 740ml bottle of slurry and then repitching about a quarter or half of that, potentially via a starter, a couple of months later isn't going to pose any major problems. Thanks!

[headmaster]

G'day Happy,

I have been doing what you have described for at least three years now, and have managed to run some for well over ten generations, and only using a new pack because I thought I'd better, rather than risk mutation. 

As I have posted in other threads, I have found the yeasties last better in the acidic environment that they create for themselves, so at PH of around 4 to 4.5. 

When I was rinsing (with boiled cooled water) I found that the viability would decline a lot faster than simply storing the yeast cake as you find it after fermentation. The yeast seem to be happy in beer, or only mildly diluted beer. Details will be in the very long 'harvesting yeast for dummies' thread. 

I have actually managed to pitch harvested slurry some 7 months after harvest and have had a sluggish start but it did ferment out just fine. I would not recommend this however. 

The two month timeframe that Kelsey mentioned is more like what you should be looking at, before making a starter, if you are using approx 400ml of compacted yeast slurry. 

I have found one important caveat here, if you lager a beer for a while on the yeast cake, you need to factor this in to the yeast age, so best to start the clock for that two month window, from pretty much the end of active fermentation, rather than harvest date, which might be 2 to 3 weeks later if you end up lagering for a while. 

I too share your motivation for re-using the yeast, 1, I hate to tip stuff down the drain when it is perfectly good freshly incarnated yeast cells that you happen to have made yourself, and then go and pay someone up to $16 (if using liquid yeast) for a tiny amount more of what you have just tipped down the drain, when you could be making 23 litres of quality beer (AG) for around that much money. 

 

[Beerlust]

It is said that yeast viability diminishes over time. The longer you leave it in storage the lower the viability & supposed cell count for re-use. As far as a shelf life goes, they do have a long shelf life if stored correctly.

As an example of that, I recently made a starter with some yeast I've had in storage for almost 12 months (linky). As you can see from the pic, it is certainly alive & well. 

The only problem that exists from re-using yeast from slurry is you have no idea of the volume of viable yeast you have collected. Depending on the pitching rate you used on the previous brew, along with the gravity of the wort it had to ferment along with other factors can affect the final state of the yeast that remains after that brew is fermented out.

Although Kelsey's starter method is not entirely accurate either, it has a more consistent process that ultimately delivers a more consistent outcome of healthy yeast cells in good numbers for re-use over & over again. Once I purchase my stir plate, I'll be switching to this method for yeast cultivation & re-use.

Coz I wannabe a better yeast daddy! 

Cheers,

Lusty.

[Greenyinthewestofsydney]

Had a 2L starter (US05) which i decanted off and into a jar and left for 3 months when i was overseas. When i got back i made a pale ale and used it in the batch. After no activity for 2 days i panicked and made a dash to the home brew store for a new packet. The SG of the batch was 1045 and really a 1L starter would have been enough to do start in a respectable amount of time and finish. That tells me it probably lost more than 50% viability in that 3 months. From now on anything more than a month and i will make a new starter. Just to many variables regarding viability rates IMO. 

[Otto Von Blotto]

It isn't just said that yeast viability drops over time, it's an observed fact. However, I observed it to drop more slowly than the calculators would suggest when I did my stain testing. That was using yeast harvested from a starter though, perhaps the calculators are based on observations of yeast harvested from fermenter trub. I've yet to test this but I am planning to. I'll probably wait until we move house though because everything is a jumble in the current place.

[Greenyinthewestofsydney]

What yeast did you use Kelsey in the experiment? One thing i have noticed in my yeast bank which consists of vials of yeast in the refrigerator is that ale yeast tends to go off quicker than the lager yeast.

[Otto Von Blotto]

The main experiment used Budvar Lager yeast but stopped testing it after about 45 days*. At that stage its viability was observed at around 85%.  However I did some one off stain testing on one or both of the ale strains I had (and am still using) after they'd been sitting in the fridge for about two months using dregs from the jar after tipping it into a fresh starter, and observed viability around 78-80%. I know I did one on the 1272, but can't remember if I tested the 1469 or not.

*I was doing daily tests and it became a pita. I am planning to do it again but testing weekly instead. Hopefully that will result in a longer period, hoping to test up to 6 months.

Cheers

Kelsey

[Beerlust]

Hi Greeny.

11 hours ago, Greeny1525229549 said:

Had a 2L starter (US05) which i decanted off and into a jar and left for 3 months when i was overseas. When i got back i made a pale ale and used it in the batch. After no activity for 2 days i panicked and made a dash to the home brew store for a new packet. The SG of the batch was 1045 and really a 1L starter would have been enough to do start in a respectable amount of time and finish. That tells me it probably lost more than 50% viability in that 3 months. From now on anything more than a month and i will make a new starter. Just to many variables regarding viability rates IMO. 

Would I be correct in assuming this 2L starter was formed by yeast derived from trub off of a previous brew, as opposed to a freshly sourced sachet of yeast? I'm guessing it was sourced from a previous brew. 

Did you pitch the decanted yeast into a starter before pitching it into the "pale ale" brew? I'm guessing you didn't. 

The reason you had no activity for 2 days is because you never tested the viability of your stored yeast to begin with by introducing it into a starter prior to pitching it into a full volume brew wort. I'm guessing the viability was low based on the previous brew it was sourced from (hypothetically).

When re-using yeast from trub I feel it is foolhardy to "blind pitch" it into a new brew & believe everything will work out OK every time. The starter method prior to pitching liquid based yeast (either first point sourced or home grown) appears to be an important step to go through for numerous reasons including a viability test, a growth of cell count, & placing the yeast into an active state prior to pitching.

Any liquid yeast(s) I have stored go into a starter before I look to pitch it into any main brew wort of mine.

Just my 2 cents.

Lusty.

[Greenyinthewestofsydney]

Hey lusty

It was a starter from a stored yeast which was kept from an overmade starter using a new packet of US05. So no slurry/trub influence in there. And only 2nd generation. 

No i didn't make a new starter based on my assumption that the 2L starter after 3 months would probably have enough viability to do the job. But appears that it lost more viability than i expected.

I do agree that it is good practice to make a new starter everytime. Takes away the blind faith aspect. 

Cheers.

[Beerlust]

1 minute ago, Greeny1525229549 said:

No i didn't make a new starter based on my assumption that the 2L starter after 3 months would probably have enough viability to do the job. But appears that it lost more viability than i expected.

Never assume. It makes an ass out of you & me, as the saying goes. 

Interesting choice of words there. What do you class as "overmade" when talking about a starter?

I'm not pickin' on ya mate. I've been the victim of my own mistakes that very much mirror what you have done here. I just learned from them & don't risk it anymore.

Any stored yeast you've harvested, throw it in a starter & smell it before you pitch it into any full brew wort you wish to use it on (IMHO).

Cheers,

Lusty.

[ben 10]

I've pitched over 3 months old without issue

[Otto Von Blotto]

I'd guess overmade means like what I do with mine - make them bigger than necessary for the batch and harvest the excess.

[Greenyinthewestofsydney]

Yep. I overmake starters too. And usually try to overmake so that i can get two starter makers harvested so each generation gives me two starters not one. So 10 generations will give me 20 starters etc..

[Titan]

Kelsey, where do you get the trypan blue? Looked internet and cant see supplier.

[Otto Von Blotto]

I got it off Amazon in the US, was about $100 (most of that was shipping, not sure why so expensive). Had a bit of a fiasco getting it in actually because the company name had Bio in it and the customs here thought it contained biological matter. Had to get the company to send a declaration that it didn't. 

Apparently it's used in blue fountain pen ink which I have but I've yet to actually do a stain testing with ink. Be interesting to see if it yields the same results. 

Methylene blue can be used as well although it's apparently less accurate at lower viabilities.

[Titan]

Thanks mate i will try and source some here. Have also heard malachite green can be used and is used in aquarium fish medicine. Might have a look at this also.

[Otto Von Blotto]

I had a look here first as well but didn't really have much luck. The places I looked at seemed to only sell it to commercial customers. Hope you have better luck, should be cheaper if you can get it here. Mind you, the amount used in a stain test is bugger all so it would last ages.