Yeast Viability Over Time

[Otto Von Blotto]

Hi guys,

 

I've begun doing my daily viability testing on a sample of 2000 Budvar yeast that was taken from a starter made up last week. So far up to 7 days, with some interesting results. I figured I'd start a new thread for this topic and just keep updating it periodically as the data grows.

 

These are the results of the first 7 days. All counts were done with at least 1500 total cells, most over 2000. Interestingly, the viability dropped quite a bit over the first few days then for some reason increased a little. I don't know why but it will probably make more sense once I get up to the 30-40 and more days, and can more easily work out an average drop in viability.

 

These are the percentages so far:

After 1 Day stored - 97.41

2 Days - 94.14

3 Days - 92.94

4 Days - 91.5

5 Days - 89.98

6 Days - 91.16

7 Days - 91.32

 

So far, these figures roughly line up with the yeast calculator figures, but what I'm interested in is whether that continues the longer it's stored. When I did some stain testing on cultures that had been in the fridge for 2/3/4 months (when making starters), they returned results much higher than the calculator suggested.

 

I'll update again after 14 days.

 

Cheers

 

Kelsey

 

[ChristinaS1]

Nice one Kelsey. Thanks!

 

I'll be following this thread as it goes along, for sure. I will be interested to see what happens after the two week point. IIRC, White and Zainasheff, in their book "Yeast," recommend using slurry within two weeks, which I assume means viability is pretty good until then. But you're testing samples from a starter, not slurry, so it is probably "younger" than most slurry, by ~10-14 days, nor will your yeast have been exposed to hops, the way yeast in slurry is.

 

Cheers,

 

Christina.

 

[Otto Von Blotto]

Nice one Kelsey. Thanks!

 

I'll be following this thread as it goes along' date=' for sure. I will be interested to see what happens after the two week point. IIRC, White and Zainasheff, in their book "Yeast," recommend using slurry within two weeks, which I assume means viability is pretty good until then. But you're testing samples from a starter, not slurry, so it is probably "younger" than most slurry, by ~10-14 days, nor will your yeast have been exposed to hops, the way yeast in slurry is.

 

Cheers,

 

Christina.

[/quote']I'd agree with that too Christina, the non exposure to hops is one reason I prefer my current method for harvesting and re-using yeast, as well as the lower gravity wort that it has fermented in the starter itself.

 

My only concern with this testing is that the jar containing the sample has to be swirled up every day to be able to take a drop or two of yeast for testing. I don't know whether this has any effect on it losing viability faster or not, but so far I don't have any way of taking a crapload of samples into individual containers in order to not have to swirl it up each day. I guess I'll find out when I get to the two month stage - last time I tested a yeast stored that long it came out at 88.6% viability. I don't expect this one will but you never know.

 

Cheers

 

Kelsey

[ImaginativeName]

Nice one.

 

Thanks for sharing.

[Otto Von Blotto]

The viability has stabilised over the last few days. I missed taking a sample slide at 9 days old, but since 7 days it has hovered around 91% without really moving much. Today's sample is 11 days old, and I haven't counted it yet but from the looks of the pictures it will be around the same. The 10 days sample measured 90.77%. The calculator is saying 88% so it is starting to drop away further than my testing is showing with a real life sample. I'm finding this really interesting actually, even though the picture editing/cell counting is a bit tedious .

 

Cheers

 

Kelsey

[Otto Von Blotto]

Update after 14 days stored. Viability is still hovering around 89/90%. Today's result was 89%, vs. the calculator at 86% for the same time. Not a lot of difference yet, but it is still early in the timeframe. I have been tracking it in a graph as well to give a more visual look at the rate of viability drop, this is a snap of it after 14 days of testing. After a reasonably fast drop at the start it has definitely stabilised in the past 9 or 10 days.

 

 

Cheers

 

Kelsey

[Greenyinthewestofsydney]

Looking forward to seeing what the effects are over the next 20 or so days. I was expecting more of a drop off to be honest. I have kept starters and slurry in the fridge and totally agree with Christina and yourself that the slurry goes off much much quicker than an unhopped starter.

 

By the way. What was your impression of a pilsener made with the 2000 yeast compared to the 2001?

[Otto Von Blotto]

I'm interested to see what the results are as well as the time goes on. I did do a stain test on a sample of 1272 recently which came out at 88.6%, after being in the fridge for 2 months. I can't imagine the viability of this Budvar sample staying up there for that long, but as noted I think the daily agitation of it might be affecting it a little too. That other culture simply sat in the fridge undisturbed the whole time, under more beer too. Next time I do this I'll refine the method a bit, at least in terms of how much beer the yeast is stored under. I don't really have the means to store yeast in daily testing containers.

 

Anyway, I had a glass of the pils fermented with the 2000 yeast earlier tonight and it's slightly different to the 2001 fermented batches, but still very enjoyable. Possibly a teeny bit fruitier, but otherwise pretty much the same. I'll be keeping this one going for a while yet I think.

 

Cheers

 

Kelsey

[ChristinaS1]

Looking forward to seeing what the effects are over the next 20 or so days. I was expecting more of a drop off to be honest. I have kept starters and slurry in the fridge and totally agree with Christina and yourself that the slurry goes off much much quicker than an unhopped starter.

 

I actually don't know that slurry goes off more quickly than unhopped starter or not' date=' but I suspect it does. Kelsey, I would be very interested to see you do another series on hopped slurry in the future, if you were up for it. Hope you are. Your findings would carry a lot of weight with me. [img']biggrin[/img]

 

I think those results, compared to your current ones, would be worthy of being published, that is if there is a significant difference. Maybe you could get an interview on Brew Basic Radio, or some other brewing program?

 

Cheers,

 

Christina.

[headmaster]

Great stuff Kelsey, awesome experiment.

 

Very interested to follow the results.

 

Like I have mentioned elsewhere, now that I have started to store my harvested yeast slurry almost 'as is' by not adding too much water (maintaining low PH of finished beer of around 4-4.5) I have seen great improvements in yeast viability when storing them in the fridge.

 

Christina, I think you are missing out on some flexibility by only assuming these slurries last a couple of weeks. I am finding 4 months in the fridge is no big deal, but you need to have a decent amount to start with, like 300-400ml of compacted yeast slurry if looking at those timeframes, and a pretty stable 2-3°C.

 

I have also found that when storing under 'beer' or maintaining these low ph levels, there is much much less gas produced during storage, pretty much negligble. Before, when I was adding quite a bit of boiled cooled water as per the 'harvesting for dummies' method, I was having to burp the passata jars in the fridge regularly, and they also started overflowing and going nuts when you let them warm up a bit. Possibly autolysis related. This pretty much does not happen now that I store under beer or only add very small amount of boiled water to swirl up the yeast cake.

[Otto Von Blotto]

I can certainly do another series with slurry from a fermenter Christina, I'll put it on the list. I'll be continuing this one until either 6 months old or the jar of yeast runs out, whichever comes first. It normally takes me about an hour to prepare the slide, take 10-15 pictures*, edit the pics and then count the cells, so I'm only doing one culture at a time so it doesn't take up too much of my time.

 

Today's test came out at 91.67% after spending 2-3 days around 89%. The blue trend line is in the graph for this reason, to determine an average drop over time, since some days there will be slight increases and decreases.

 

I've also noticed hardly any gassing when storing yeast under 'beer' in the jars. I still leave the lids slightly loose just in case though.

 

*I take this many pictures to give a better overall impression of the slide itself. All counts are a minimum of 1500 cells, most over 2000. I had two pictures in today's lot where the viability was vastly different in each one. One would have been over 95% viable while the other was probably somewhere around 80%. The results would be rather inconsistent day to day if I just used one photo per day. It is a bit time consuming but worth it in the end.

 

Cheers

 

Kelsey

[Greenyinthewestofsydney]

Looking forward to seeing what the effects are over the next 20 or so days. I was expecting more of a drop off to be honest. I have kept starters and slurry in the fridge and totally agree with Christina and yourself that the slurry goes off much much quicker than an unhopped starter.

 

I actually don't know that slurry goes off more quickly than unhopped starter or not' date=' but I suspect it does. Kelsey, I would be very interested to see you do another series on hopped slurry in the future, if you were up for it. Hope you are. Your findings would carry a lot of weight with me. [img']biggrin[/img]

 

I think those results, compared to your current ones, would be worthy of being published, that is if there is a significant difference. Maybe you could get an interview on Brew Basic Radio, or some other brewing program?

 

Cheers,

 

Christina.

 

I can't 100% prove it either. Only visual appearance (Slurry tends to go a darker grey quicker than an unhopped starter). And an apparent slower start when pitching for around the same amount of yeast but Id sure love Kelsey to prove or disprove the theory one day.

[ChristinaS1]

. Like I have mentioned elsewhere' date=' now that I have started to store my harvested yeast slurry almost 'as is' by not adding too much water (maintaining low PH of finished beer of around 4-4.5) I have seen great improvements in yeast viability when storing them in the fridge.

 

Christina, I think you are missing out on some flexibility by only assuming these slurries last a couple of weeks. I am finding 4 months in the fridge is no big deal, but you need to have a decent amount to start with, like 300-400ml of compacted yeast slurry if looking at those timeframes, and a pretty stable 2-3°C.

 

I have also found that when storing under 'beer' or maintaining these low ph levels, there is much much less gas produced during storage, pretty much negligble. Before, when I was adding quite a bit of boiled cooled water as per the 'harvesting for dummies' method, I was having to burp the passata jars in the fridge regularly, and they also started overflowing and going nuts when you let them warm up a bit. Possibly autolysis related. This pretty much does not happen now that I store under beer or only add very small amount of boiled water to swirl up the yeast cake. [/quote']

 

My method is pretty much the same as yours John; I just store the yeast "as is," under green beer. I am thinking about trying some 1469 liquid yeast this fall and might want to experiment with storing longer. But just some clarification please: when you say you use 300-400ml of compacted yeast slurry for those longer time frames, how much are you starting out with?

 

I find your observations of diluted slurry very interesting John. Just wondering if you can recall whether those batches where you stored the yeast under a combo of water and green beer took off quicker vs the ones you stored as is, under pure green beer? From your observations is sounds like the yeast never went dormant in the diluted slurry; the surviving yeast seemed to remain active, busy eating their dead sisters. That makes me wonder if, even though the number of viable yeast in diluted slurry might drop at a faster rate, they make up for it (to a point) with more vitality? Mind you, the diluted slurry took more care and maintenance, so that is a consideration.

 

If the above is true, I wonder what the exact pH level is that triggers the yeast to go dormant, vs remaining active? There is a big difference in acidity between pH 4.0 and pH 4.5. The pH scale is logarithmic, so a pH of 4.0 is ten times more acidic than pH 5.0. Math is not my strong point, but doesn't that mean pH 4.0 is five times more acidic than pH 4.5?

 

I have not read, "Harvesting for Dummies." Can you provide a link? Or are you talking about Antiphil's method?

 

This makes me wonder if pH is the reason that yeast saved from unhopped starter slurry seems to last longer than yeast saved from the bottom of a FV....I am sure an unhopped slurry is less acidic than that a hopped slurry. Kelsey, do you have to burp your saved starter slurry?

 

Cheers,

 

Christina.

[Beerlust]

...& I'll be there to 'pounce' & 'profiteer' after you've done all the hard work & research Kelsey.

 

Keep up the good work mate!

 

Seriously though, very interesting stuff & I personally would be interested in attrition rates & yeast behaviour patterns with yeast drawn from "clean" starters vs yeast stored from slurry under beer.

 

There's a guy down here in SA that I should put you in contact with as he would love this sorta stuff I reckon.

Pirate knows who I'm talking about too I think.

 

Cheers,

 

Lusty.

[Otto Von Blotto]

Thanks mate! Yes I'll be doing another series with slurry straight out of the FV next. To keep things simple I'll do it with the same yeast strain.

 

I will do some further testing from starters with my other two regular strains as well and see if they behave differently to the Budvar strain. I'll also compare results from this daily testing against the culture that has just sat undisturbed in the fridge, next time I use it in a batch.

 

Cheers

 

Kelsey

[Otto Von Blotto]

Update after 22 days stored, simply put the viability is still hanging around that 90% mark. I missed three days testing over the weekend and Monday due to a night out on Saturday, so Friday's testing was 90.78%, yesterday's 90.07%, and today it measured 89.94% viable. This is the first time it's been under 90% in 8 days. The calculator suggests it should be 80% at this point, so the gap is beginning to widen.

 

In some ways I'm not surprised given the results I've had from stored yeast 2-3 months old, but I would have expected there to be some drop off. Since 4 days old it has been as high as 91.67% and as low as 89%, just jumping around between those numbers, so reasonably stable. I'll update again in another week or so when it will be basically 1 month stored. The calculator suggests it should be 75% viability after a month, but I think it will be higher than that. The way it's been going it'll probably only drop another 1 or 2% in that 8-9 days.

 

Cheers

 

Kelsey

[headmaster]

Sorry about the late response Christina, have been flat out busy.... BTW I'm Mark, but thanks for having a crack at my handle in any case, you weren't far off at all :-) I shoudl sign off with my actual name more often :-)

 

But just some clarification please: when you say you use 300-400ml of compacted yeast slurry for those longer time frames' date=' how much are you starting out with? [/quote']

 

Starting out with 750ml jar filled to the top with yeast from yeastcake about an hour after racking beer off, I tend to rack most of the beer off, add about 750ml boiled cooled water to dilute the cake enough to make it liquid to then pour into the 750ml passata jar (in case you are not familiar, Passata is italian tomato sauce for pasta etc, basically tomato in a jar without skin or seeds)

 

In a fridge over a few days this settles out to almost half the jar, hence the 300 to 400ml compacted.

 

I find your observations of diluted slurry very interesting John. Just wondering if you can recall whether those batches where you stored the yeast under a combo of water and green beer took off quicker vs the ones you stored as is' date=' under pure green beer? From your observations is sounds like the yeast never went dormant in the diluted slurry; the surviving yeast seemed to remain active, busy eating their dead sisters.

 

[/quote']

 

From memory, I found the less diluted yeast to easily outperform the diluted, my notes where applicable confirm that as well.

 

I have not read' date=' "Harvesting for Dummies." Can you provide a link? Or are you talking about Antiphil's method?

[/quote']

 

 

Yes Antiphils method. I no longer endorse that method or any yeast washing really, unless you are going to adjust PH of washing water with acid, which sounds too risky (for the yeast mainly)and complicated.

 

This makes me wonder if pH is the reason that yeast saved from unhopped starter slurry seems to last longer than yeast saved from the bottom of a FV....I am sure an unhopped slurry is less acidic than that a hopped slurry. Kelsey' date=' do you have to burp your saved starter slurry?

[/quote']

 

Because I have had harvested yeast last 4 months in the fridge no worries, I reckon it's possible it may last just as long as unhopped from a starter, who knows maybe it will last longer. Will depend on variables like ABV etc of course, but consider all of those nutrients from the slurry that the yeast can snack on if they decide to wake up just a bit.. There will be more dead yeast cells in particular in the slurry harvested from the beer.

[ChristinaS1]

Sorry I got your name wrong Mark.

 

I guess we'll have to wait for Kelsey to repeat his testing with yeast harvested from a FV.

 

BTW Kelsey, it will be interesting to see if the viability over time plots out for ale vs lager yeast, since ale yeast would be further from their ideal temps than lager. Your test of that two month old sample of 1272 would seem to indicate there may not be much difference.

 

IIRC I read somewhere, might have been on Brew Kaiser site, that freezing yeast kills 50%, but so does storing yeast in the fridge for six months. The take home message was that if you are going to store yeast >6 months it is better to freeze it....I cannot recall how he was storing the yeast in the fridge, if it was hopped or un-hopped slurry, or under green beer or rinsed.

 

Cheers,

 

Christina.

[Otto Von Blotto]

Yes, I do have plans to do a series with 1272 and also 1469, so whichever of those two is next in line when I finish the FV slurry series will be the ale yeast that is first tested according to my usual storage methods.

 

I hope this little jar of yeast I'm using for my testing lasts 6 months, because it'd be interesting to see how viable it is after that time. In any case, in normal circumstances I don't store my yeast any longer than 2-3 months at a time anyway, because I'm always fermenting with each of the three strains I keep; first is lager (pils), then I do a red ale or ESB with 1469, then an APA with 1272. As a result I have no plans to get into freezing yeast for long term storage, it's just not necessary for me to do it.

 

Cheers

 

Kelsey

 

 

[Otto Von Blotto]

Hi guys,

 

I've been a bit distracted by life shit over the past week or so and haven't done any stain testing until today, so it's been a 12 day break. The last testing after 30 days stored recorded a viability of 87.95%, and today after 42 days stored I recorded a result of 83.68%. At the moment this works out to an average daily decrease of 0.39%. Hopefully I can get back to testing every day again now, or at least most days - I won't be doing any over this coming weekend with the grand final Saturday, birthday drinks Sunday and recovery day Monday .

 

The calculator suggests 68% for the same 42 day time frame.

 

Cheers

 

Kelsey

[ImaginativeName]

Great info Kelsey.

 

Cheers

 

JP