How to tell how much yeast has grown?

[h-bar]

Is there a way to visually "guess" how much yeast has grown in a starter? I have a friend who works in a biochem lab who has counted cells for me in the past, but she's busy and I'd prefer to not take time away from her research.

I am also interested in growing excess yeast that could be stored for later use. If anyone has any insight on this, I would greatly appreciate it.

 

[TAK]

I use yeastcalc to estimate growth bases on viability. You can roughly get an idea of growth if you take the numbers you expect from the calculator and couple that with the volume of the yeast cake after cold crashing. I'm not sure how accurate this is, but the yeast cake definitely increases when you step up.

I'd be interested to hear what others say though. I know roughly what to expect from my starters, but I don't really know what the yeast cake volume would look like straight out of a smack pack.

 

[LLBeanJ]

As long as you have reconciled the fact that it is just a guess, then yes. If you have a decent estimate of your starting count, say by buying a new yeast vial or smack pack, then making a starter from that, you can use yeastcalc.com to come up with an estimate of how much you will have after the starter has completed.

As an example, say you make a 1L starter from a fresh vial. According to yeastcalc, based on the viability date on the vial and the fact that you assume that you're starting with 100B cells, let's say that you should have 200B cells when the starter completes. Now, maybe you need 160B to pitch in your beer and you want to save the rest for a future starter. So, you're pitching 80% and keeping 20%.

A 1L starter + the 100ml or so of yeast and liquid in a vial of yeast means that you should have a total volume in your starter of about 1100ml. 20% of 1100 = 220ml. It just so happens that an 8 oz = 218ml, so you swirl up the starter to get all the yeast into suspension and fill up a sanitized 8 oz mason jar with liquid. It's a reasonable guess at this point to assume that your jar has about 40B cells in it and there are about 160B remaining in the starter flask... give or take. Label the jar with the quantity and date the starter finished and save it for next time.

After a day or two in the fridge, that 40B cells in the jar will settle and you'll be able to see what about 40B looks like, volumewise, in an 8 oz mason jar. After doing this a few times, you'll be able to take fairly educated guesses on how much a particular amount of yeast represents in billions of cells. Many times I've looked at a jar and thought to myself: "there's about 1/2" of yeast, so I'm guessing that's about 100B cells right there", then used that number as a starting point for yeastcalc. Is it really? Probably not, but it's close enough to get the job done.

That's what I do and it's served me well, as far as I can tell. I don't worry about being off, cuz if I did I'd drive myself insane.

 

[h-bar]

That's extremely helpful. I'll definitely be using yeastcalc and LLBeanJ's method in the future when starting from a vial. However, what I'm working with at the moment is yeast that came from a Westmalle Dubbel bottle (I liked the beer so much I decided I wanted to make a clone, and what better yeast to use than the yeast it came with!). After one week, I had about 1/4" of sediment in the bottom of a half gallon growler. I decided to take out about 75% of the volume and replace it with fresh DME solution. After four days, I have about an inch of sediment. Smells healthy, looks good.

Ideally, I want to save half for later, perhaps to use in a different beer altogether, and use the other half for my clone. Right now, I'm trying to decide if I have enough to divide into two containers, or if I need to refresh the solution again. I know the information I'm giving probably isn't very helpful, but it's all I have to go on. Thank you for the advice so far, I really appreciate it.

 

[LLBeanJ]

I believe there are about 4.5B cells per ml of clean yeast cake. If you have a smallish container that's graduated in ml's, you can use that to come up with an estimated cell count. For example, 80ml x 4.5 = 360B cells. Close enough for a ballpark guess.

 

[h-bar]

Using that, I have an estimate of about 400B! Thank you thank you!

 

[LLBeanJ]

Using that, I have an estimate of about 400B! Thank you thank you!

Also check out mrmalty.com. It's a great tool for working with slurry.

http://www.mrmalty.com/calc/calc.html

 

[h-bar]

Some unfortunate news. When I was about to transfer the yeast into some mason jars, I noticed an odd smell. Before, I was smelling near the airlock and it seemed fine. I tasted a bit of the starter, and sure enough, it was sour. Dang it! I guess this is a bit off topic now, but is the glass container I was using ruined? I know sour beers can "ruin" equipment.

 

[LLBeanJ]

No, just give it a good cleaning and sanitizing. That's one of the benefits of glass.

... and sorry to hear about your yeast.

 

[bob3000]

Starters are nearly always sour. It is nothing to worry about. Its because of the lack of hops.

 

[LLBeanJ]

My experience is both yes and no on that. Starter beer should be somewhat malty sweet due to the lack of hops. But, the yeast itself can add some sourness to the beer depending on how much is in suspension. I don't generally make it a habit to taste my starter beer, but on the few occasions where I have, it wasn't what I would describe as sour.

 

[h-bar]

The last time I grew yeast, I didn't taste the starter, but I didn't smell anything off either. I somewhat suspect that the contamination happened when I added fresh DME to it. It smelled fine before I did that.

 

[LLBeanJ]

Did you boil the DME before you added it?

I agree that a funky smell is a bad sign. Of course, some strains do have an inherent funkiness to them, so it's not always a reliable indicator that something is off.

 

[h-bar]

Yep, boiled it for 15 minutes.

 

[TAK]

I'd agree that a funky starter is not necessarily a sign of trouble. When I first began making starters I smelled and tasted them. Some were clean, but others were just off. Nonetheless, never carried through to the beer. I think the fact that it's unhopped, is riddled with yeast, and if you're on a stir plate, highly oxidized, it's not surprising that the starter is off. Doesn't imply it's an infection. If you took reasonable sanitation steps, you're fine.

RDWHAHB

 

[h-bar]

I'd agree that a funky starter is not necessarily a sign of trouble. When I first began making starters I smelled and tasted them. Some were clean, but others were just off. Nonetheless, never carried through to the beer. I think the fact that it's unhopped, is riddled with yeast, and if you're on a stir plate, highly oxidized, it's not surprising that the starter is off. Doesn't imply it's an infection. If you took reasonable sanitation steps, you're fine.

RDWHAHB

Good to know for the future. If sourness isn't necessarily an indicator of infection, what is? I mean, other than mold fuzz or anything glaringly obvious like that. I'd really prefer to avoid souring any equipment that I don't want to use for wild beer only.

 

[LLBeanJ]

I'd say sourness or a foul smell is a pretty good indicator, but they are subjective. Unless you have experience with a particular strain, in terms of how it should smell or taste, you have nothing to compare it to. Bottom line is that if you're not comfortable with it and are not willing to accept that it might ruin your batch, then don't use it. If you don't care, then throw caution to the wind and brew with it. If you're not sure, but would rather test it first, try fermenting a mini batch, say a 1g batch of wort with hops, which would be an easy stovetop process. If it turns out all right, you can then feel comfortable brewing the main batch and add the mini batch to it at time of bottling/kegging if you're so inclined. There may be easier ways to test (e.g., using a microscope, but you need to know what you're looking for), but without some lab equipment, a trial run seems like it would be a simple way to confirm your yeast health one way or the other.