Decanted yeast stater analysis

[Jordan Penard]

Hi Guys,
I have been doing yeast starters for a while now, and I recently started banking yeast in the freezer requiring a further level of decanting.
My process is as follow, make a starter, leave it on stir plate for 12h, leave it at room temp stir plate off for 12h, move it to the fridge for 24h, remove most of the liquid keeping only the decanted yeast with a little liquid, stir the remain and transfer to a smaller container, decant a further couple of hours, use a seringue to remove as much liquid as possible to be left with just the deposited yeast ready for banking.

Now, my question relates to my second decanting step, after an hour I can see darker residue at the bottom of the jar, with a thin lighter in colour layer starting to build up. I have attached a picture of that.

What do you think the darker and lighter colour means ? This is from a fresh and healthy starter made from 5ml of healthy yeast pitched into 0.5L of water with 500g of light DME.


Thanks

 

[HighVoltageMan!]

The bottom layer is trub and forms fairly quickly. Healthy yeast is a pinkish tan color, dead yeast is a greyish color. If you see a grey layer on top of the healthy yeast, it's usually from an older package of liquid yeast. If you do a starter from dry yeast, you rarely see that. Typically the bottom layer is trub, the next layer is yeast, the grey layer forms last.

It looks like most of your heathy yeast is still in suspension.

 

[Jordan Penard]

Interesting, so it looks like I have a lot of dead yeast cells in there then. Do you expect that from a starter that fresh ? What's for sure is that those dead cells didn't come from the yeast I pitched into my starter because I pitched only 5ml, and there's something like 20ml of dead cells here, and very little healthy yeast.

What could be the reason for such a high ratio of dead cells ? Can it be that I left the starter too long out and it went through fermentation of the starter rather than stopping at the end of the growth phase ?

 

[HighVoltageMan!]

Interesting, so it looks like I have a lot of dead yeast cells in there then. Do you expect that from a starter that fresh ? What's for sure is that those dead cells didn't come from the yeast I pitched into my starter because I pitched only 5ml, and there's something like 20ml of dead cells here, and very little healthy yeast.

What could be the reason for such a high ratio of dead cells ? Can it be that I left the starter too long out and it went through fermentation of the starter rather than stopping at the end of the growth phase ?

I didn't see any dead cells in the picture. The darker layer on the bottom (brown color) is trub, sometimes called cold break. This is mostly proteins that are formed during the boiling of wort. Dead cells will drop last and form a thin grey layer on top of the tan/pink layer. Heathy yeast will flocculate (drop out) before dead cells. The dead cells are harmless and I've only gotten that layer when the liquid yeast is getting old.

 

[Jordan Penard]

Ok got it, in this case I should probably change my process to get rid of the trub then. I though that trub was only present when using grains, I didn't know it was the result of proteins break down. I guess I should decant my sanitised wort before pitching then.

Thanks

 

[HighVoltageMan!]

The trub is harmless, it just gets in the way of measuring yeast.

 

[Hawkbox]

Don't worry about the trub at all.

 

[Jordan Penard]

The trub is harmless, it just gets in the way of measuring yeast.

Correct, in this instance I want to put 5ml of yeast into a tube that I'm going to top-up with 5ml of a 25% glycerine solution for freezing

 

[Mark Farrall]

Correct, in this instance I want to put 5ml of yeast into a tube that I'm going to top-up with 5ml of a 25% glycerine solution for freezing

I wouldn't worry about the trub in your process. I'd be using the syringe to draw up 5 mL of the yeast layer to mix with the glycerine and then put in the freezer. You can then discard the remaining slurry, or use it as a starter.

I'd be interested to know how it goes if you ever build back up from the frozen yeast. It's something I keep telling myself I have to get around to as I've got a few strains I can't get commercially.

 

[Jordan Penard]

It goes really smoothly, but after some time in the freezer the yest starter takes a bit longer than usual to properly develop. The last starter I made was with a vial that has been in my freezer for around a year, and it seems that the yeast was deeply asleep as it took a good 3 days for the starter to fully mature. I haven't taken a FG reading of the beer I made with that starter yet as I haven't bottled yet, but my home made tilt Hydrometer is telling me that I have reached my target FG, so all seems good to me so far.

 

[Mark Farrall]

Awesome. What was the volume of that first starter you made?

 

[Jordan Penard]

My rule of thumb at the moment is 5ml of flocculated yeast into a 0.5L starter (500ml of water and 50g of DME) to feed a 5 to 6L batch of beer.
I did some research at the time on yeast cell concentration, propagation and grows ratio and also considering that in the 5ml of yeast at the start a good portion might be dead as it comes from my frozen bank, and I was happy with my guestimations and have been having good results so far.
If you want to put that into a 20L (5 galon) batch you might need to step up the 0.5L starter though, or use more than 5ml to start with into a bigger starter.

And about the creation of the frozen yeast bank, I do a yeast pack (Whyte Lab or Wyeastl) into a 0.5L starter, put most of it in vials to freeze, that's by generation 1, and keep 5ml to do a second starter and freeze the result as my generation 2.
When I want to make a beer I use a generation 2 vial, when I run out of gen2 vials I make a new starter with a gen1 vial to freeze a new batch of gen2 vials.
For more details on that I recommend the following article : http://www.homebrewnotes.com/making-a-frozen-stock-yeast-bank/

 

[Hawkbox]

That's largely how I've done it. I kind of went overboard freezing starters, I don't feel it's really worth the effort to freeze a 34/70 starter for example considering how cheap the yeast pack is.

 

[Jordan Penard]

Yeah I agree, in general dry yeast will cost less to buy than the price of freezing it (cost of a sterile vial plus glycerin).
Also you can easily throw a few pack of dry yeast in the freezer as they are so you always have some ready for when you need them.

In my case I didn't start freezing liquid yeast to save money, I did it to always have supply for when I need them. But cost is of course also a big factor.

 

[Hawkbox]

It was a little of both for me, I ended up doing it to have hard to get ones and then did it for everything I had. Which was a bit excessive. I have barely used the frozen yeast.