Yeast Starter Question

[argon]

One thing i've always wondered about is viability.

Let's say i harvest some top crop, say 20mL, from an active fermenting batch then store under water for a couple of months. I grab the stored yeast out of the fridge, look at the date of a couple of months back, go to MrMalty and he tells me that it's now at 10% viability. I then step it up to 250ml, to 2.5L... what's my viability now?... surely it still couldn't be 10%. I would have thought that the viability of the yeast I have now is pretty much 100%. Am i right?

 

[Wolfy]

I grab the stored yeast out of the fridge, look at the date of a couple of months back, go to MrMalty and he tells me that it's now at 10% viability. I then step it up to 250ml, to 2.5L... what's my viability now?... surely it still couldn't be 10%. I would have thought that the viability of the yeast I have now is pretty much 100%. Am i right?

That's correct, the viability is simply a measure of how many of the total yeast cells are still alive. And it relates to the yeast you are starting with, since some of it will have died because it's been in storage for some time. However, by making a starter (and stepping them) you're essentially breeding larger number of healthy and viable yeast. As a result by the time you pitch your yeast it will be close to 100% viable (unless you then store the starter for a week or longer and the yeast cells start to die again.)

 

[cdbrown]

Given that your slurry is now more than 1-2 weeks old, it would be best to make a starter.

However, you'll need a starter size of about 4L to close to the 400billion cells they are suggesting (I assume it's a double batch?) A 2L starter, on a stir-plate will give you somewhere around 200billion cells, which is only half what BS suggested.

Since I use a stir-plate and do not use the same wort as my beer, I always let the starter fully ferment, settle, decant the spent starter beer and pitch only the yeast.

That's strange as when I use the yeast starter tool in beersmith, I select slurry, set the date to 03/08 and it says I need 0.35L of slurry. The starter volume using liquid yeast recommends 2L on a stir plate (note that this changes depending on the date of slurry so I'm assuming it's calculating the cell based on slurry and not smack packs).

Is it not possible to have more cells /L than 100B? I don't think I have anything to ferment 4L in, especially something that would go on the stir plate. Could I do a 2L starter, ferment it out, decant liquid and store majority of slurry, add more wort and ferment that out, decant liquid and use both stored slurries?

 

[mika]

As I understand you're limited by how much the yeast will grow within a given volume. ie Pitch 2L into 4L and there's so much yeast that by the time it's started to multiply, the rest of the already existing yeast has processed all the sugars. There used to be an old rule of thumb about a 5 fold increase (or was it 10 fold) required to see any significant cell growth.
So a small (~100mL) pitch from your fridge into a 2L starter is fine.
If you can't build 4L in one go, you'll need to build concurrent starters. If you do them one of the after, the first pitch will be dormant by the time the second pitch is ready to go.
Interestingly enough, on a recent Brewstrong or CYBI show, Jamil mentioned that once the starter got to be around 20% of the wort volume, he'd decant to avoid the starter wort tainting the resultant beer. So with a 4L starter (20L batch), you'd need to decant and the only way I know of doing that is to cool it right down (so everything goes to sleep) and decant the wort off the top. So in that case you wouldn't be pitching an active starter anyway.

 

[manticle]

Tenfold from my reading*

* Actually my possibly false memory of my reading

 

[argon]

Thought it was 10 for ale strains, 5 for lager.

 

[Thirsty Boy]

That's strange as when I use the yeast starter tool in beersmith, I select slurry, set the date to 03/08 and it says I need 0.35L of slurry. The starter volume using liquid yeast recommends 2L on a stir plate (note that this changes depending on the date of slurry so I'm assuming it's calculating the cell based on slurry and not smack packs).

Is it not possible to have more cells /L than 100B? I don't think I have anything to ferment 4L in, especially something that would go on the stir plate. Could I do a 2L starter, ferment it out, decant liquid and store majority of slurry, add more wort and ferment that out, decant liquid and use both stored slurries?

What wolfy is saying is that your slury is now less than optimal - not only from a number of cells point of view, but also from a yeast health point of view. So instead of pitching the slurry, with which you can probably still get enough viable cells by plugging dates into beersmith and compensating... A better course would be to simply use some of the slurry as a way to start a new starter sequence and end up with nice new, viable, vital yeast rather than sickly slurry yeast.

To get the rit amount of cells, you need the 4L starter... But the size hasn't really got anything to do with the slurry you start with.

Its easier to think about this stuff in raw cell numbers.... How many cells do you need. How much slurry gives you that many cells OR how big a starter gives you that many cells. Once you have a common ground (the actual number of cells) then the differing volumes of starters, slants, slurries etc are all just a matter of converting.

 

[jkmeldrum]

Well it looks like I've stirred things up a bit...better do some more reading myself!!

One last thing I've been wondering about though...if I step up from a small starter to a bigger active starter, then split that in half, use half in a brew now and then store the unused half in the fridge...is that still generation 1?

If so, if I continue to do this and increase my starters before each brew and always preserve some, is that a safer way of maintaining a purer strain of yeast, as opposed to taking some of yeast cake out of the bottom of the fermenter after a brew is finished (and cleaning the yeast)?

I'm mainly asking because I want to keep a viable supply of the Wyeast 1469 that I've now got for future brews.

Cheers

Molly

 

[Thirsty Boy]

Well it looks like I've stirred things up a bit...better do some more reading myself!!

One last thing I've been wondering about though...if I step up from a small starter to a bigger active starter, then split that in half, use half in a brew now and then store the unused half in the fridge...is that still generation 1?

If so, if I continue to do this and increase my starters before each brew and always preserve some, is that a safer way of maintaining a purer strain of yeast, as opposed to taking some of yeast cake out of the bottom of the fermenter after a brew is finished (and cleaning the yeast)?

I'm mainly asking because I want to keep a viable supply of the Wyeast 1469 that I've now got for future brews.

Cheers

Molly

I dont know if you would still call it generation 1 - but in my opinion, yes, that would be a better way than taking yeast from a complete fermentation. Do some searching on "yeast farming" or "yeast storage" and you will find a wealth of different techniques. A popular, and probably better IMO way to do it would be to give an amount of the yeast you currentLly have a bit of a wash/rinse in pre-boiled and cooled water, then split the clean yeast you are left with into a few containers and store them under some cooled boiled water. Each time you want to use some yeast, grow a fresh starter from one of the "splits"

If you want, you could then take the last of the splits, grow a starter out of it and re-split... But most people are probably opting to renew their supply from a fresh pack of yeast to make sure that their yeast is still performing the way the strain is supposed to.

So you could split a fresh pack (or your current yeast) into 6 jars, grow a starter from each jar for your first fermentation, directly re-pitch some slurry from the bottom of each of your generation 2 and even 3 fermentations - and thus get 12 to 18 brews out of every $10 packet of yeast without ever having serially re-pitched for more than a generation or two.

There are lots of different ways to store yeast, you kust have to find one that you are happy with that suits the amount of effort you are willing to put into saving your money.

Cheers

TB

 

[Nick JD]

With regard to maintaining yeast strains - I think people overestimate genetic mutation; and underestimate comtamination.

 

[Thirsty Boy]

i think people tend to underestimate both.

Its not so much rampant mutation and complete change thats the issue, as much a mild "drift" in the brewing properties of the yeast.

Depending on how you harvest your yeast, some strains can start to display detectable drift in flavour, performance and physical characteristics like flocculation in as little as 4-6 re-pitches. On the other hand, certain techniques and certain strains can go hundreds and maybe thousands of re-pitches and still be pretty consistant.

In general, minimising your serial pitching is the safer/more consistant course - and to address your very valid point, so is cropping your yeast for re-pitching at a point where infection has had little to no chance to become established. Which is why i think splitting a fresh pack and working off those splits for a maximum of a couple of serial re-pitches is a sort of "sweet spot" you reduce the chances of both drift and contamination.

Of course, this all assumes you have very good control of your sanitation techniques - if you aren't 100% sure of them you just shouldn't be mucking about with yeast farming at all.

 

[bcp]

i think people tend to underestimate both.

Its not so much rampant mutation and complete change thats the issue, as much a mild "drift" in the brewing properties of the yeast.

Depending on how you harvest your yeast, some strains can start to display detectable drift in flavour, performance and physical characteristics like flocculation in as little as 4-6 re-pitches. On the other hand, certain techniques and certain strains can go hundreds and maybe thousands of re-pitches and still be pretty consistant.

In general, minimising your serial pitching is the safer/more consistant course - and to address your very valid point, so is cropping your yeast for re-pitching at a point where infection has had little to no chance to become established. Which is why i think splitting a fresh pack and working off those splits for a maximum of a couple of serial re-pitches is a sort of "sweet spot" you reduce the chances of both drift and contamination.

Of course, this all assumes you have very good control of your sanitation techniques - if you aren't 100% sure of them you just shouldn't be mucking about with yeast farming at all.

But if homebrewers can get that kind of variation, then why are the big breweries and places like Wyeast any different? Why aren't the standard CUB yeasts or White Labs yeasts changing significantly over a couple of years?

 

[Thirsty Boy]

But if homebrewers can get that kind of variation, then why are the big breweries and places like Wyeast any different? Why aren't the standard CUB yeasts or White Labs yeasts changing significantly over a couple of years?

They store their master strains in yeast banks under cryogenic conditions. Culture from that onto something like slants for medium term storage.

Bigger breweries (lager breweries at any rate) are only re-pitching a quite limited number of times before growing a fresh culture from medium term storage media, and would be carefully monitoring for drift in brewing properties and re-culturing from a long or very long term master strain as required or to some specified schedule.

Things work differently with some ale brewers - their techniques and strains can handle lots of serial re-pitching. But still, even with ale brewers, these days any brewery of a larger size would have their proprietary strains stored in a yeast bank, and smaller brewers would be operating with strains they got from a bank in the first place.

Of course, there will always be some pack of mad bastards doing it completely differently and making it work, so it all depends how much of a risk taking rebel you want to be.

 

[Nick JD]

Of course, this all assumes you have very good control of your sanitation techniques - if you aren't 100% sure of them you just shouldn't be mucking about with yeast farming at all.

No one can ensure 100% unless you work in a biohazard lab.

When you open that smack pack and pour it into your first starter, how much contamination happens there? Stepped up a couple of times ... again, contamination.

Then you take the starter and liberally pour it into the open fermenter.

I'd say your bacterial and wild yeast count is now quite a bit higher than before you opened the smack pack.

Then you do this 4 more times ... stressing the yeast on quite a few occasions.

Perfect sanitisation is not a hermetically sealed lab.

 

[cdbrown]

Made a 2.5L starter this morning with one of the jars so will see how it goes. About to order a 5L flask so I guess will get that next week at which point I could step up the starter to 4L

 

[Thirsty Boy]

No one can ensure 100% unless you work in a biohazard lab.

When you open that smack pack and pour it into your first starter, how much contamination happens there? Stepped up a couple of times ... again, contamination.

Then you take the starter and liberally pour it into the open fermenter.

I'd say your bacterial and wild yeast count is now quite a bit higher than before you opened the smack pack.

Then you do this 4 more times ... stressing the yeast on quite a few occasions.

Perfect sanitisation is not a hermetically sealed lab.

Not 100% sure of the sanitation - 100% sure of your techniques.

Of course the safest way to go is to open a fresh pack of yeast each time and take the minimum risk. But if you are going to muck about with yeast farming, then you should have a good look at your sanitation processes, you should make sure they are at the top end of the spectrum and that you are actually performing them in a thorough and well practised way.

Given that, its perfectly viable to spilt, store, farm yeast at home - and it so happens that the some of the ways that best ensure you avoid contamination, are also probably the ones that are best for keeping your yeast performing the way you expect it to.

 

[cdbrown]

Starter smell question - the starter is actively fermenting on the stir plate. It has a cidery/wine/sour smell to it. I had a small taste of it and couldn't taste anything bad so starter is still going. Prior to pitching the rinsed yeast had a smell of galaxy/citra from the previous brew. 2.5L starter with 250g ldme and I guess 30ml of rinsed yeast.

For starters does the smell matter if the taste is fine especially since I'll be decanting the beer before pitching?