Overbuilding / Top Cropping - How to Measure?

[Berube05734]

Good Morning,

I'm sure that this has been asked/discussed before, but I've searched and am coming up empty handed.

How do you know how much yeast you have made (overbuilding) or harvested (top cropping)?

For example, over the weekend I overbuilt a starter by about 50%. I'm relatively confident that I'm in the ball-park in my estimation because I was working off from the information on the yeast packet (Imperial A38) and used a yeast calculator. I provided the cell count and estimated age of the yeast and the calculator did the rest.

However, going forward and continuing with this (I'd also like to try top cropping), I'm now on my own in as far as estimating cell count because I have no way of verifying the actual number of cells I've harvested.

Should I be digging out my microscope and looking for a cell count slide...or is there an easier way? I'd hate to unknowingly and ignorantly grossly under pitch or over pitch the next batch.

Thx,

Pam

 

[VikeMan]

C&Pd from one of my posts on a different forum:

If you know the amount of cells you want to pitch, you can figure out how much slurry to use by estimating a couple things:

- Slurry Density
- Slurry Solids Non-Yeast %

Slurry Density: This is the 'thickness' of your Slurry. A very thick, compacted slurry would be about 4.5 Billion cells per milliliter. An average density might be about 2.4 Billion cells per milliliter. A thin slurry might be about 1 Billion cells per Milliliter. Factors that can affect the density include how long the slurry has been settling (and at what temperature) and the flocculation tendency of the yeast strain. This parameter estimates cells as if the slurry consists only of liquid and yeast. The accompanying parameter (non-yeast percent) accounts for the fact that there are other solids in any harvested slurry.

Slurry Solids Non-Yeast %: This is the percentage of your harvested yeast slurry solids that are something other than live yeast (such as hop particles, lipids, dead yeast, etc.) An average recommended value for this parameter is 15%. If you rinse your yeast, your value may be closer to 0. If you are pitching directly onto a yeast cake, your value might be closer to 25% or even 50%. This percentage is use to reduce the cell density specified in the accompanying parameter (Slurry Density).

Tedious example follows:

Let's say you want to pitch 300B viable cells.

And, let's say you judged the yeast cake to be of average density and you have a liter of it. So figure 2.4 Billion cells/ml x 1000 ml = 2,400 Billion Cells

And let's say the yeast cake hasn't been washed or rinsed, but looks relatively clean, so you estimate that the non-yeast % was 25% at the end of fermentation (i.e. before sitting around in the fridge).

2,400 Billion Cells x (1 - 25%) = 1,800 Billion Live Cells in the (un-aged) cake

You had decided you need 300B cells. So 300B/1,800B = 3/18 of the yeast cake. And since the cake was 1000 ml, that's 3/18 x 1000 = ~167 ml of slurry needed.

Of course, if the slurry has been sitting around, you'd want to also estimate what percentage of the end-of-fermentation live cells are still viable and throw that factor in.

It sounds complicated, but BrewCipher supports slurry re-pitching and has the parameters discussed above.

 

[hottpeper13]

Holy wow Vike, Here's what I do.
1- use brewdads calculator
2- I input the date and cell count of original pouch,and find out how much yeast I have to make.
3- So I need a 1l starter so I make a 1250 ml and save 250 ml for another starter. The calculator will tell you the final cell count,just do the math to find out how many cells are in the 250 one and put that on the cap with the date. When making the next starter use that for inputting the specs.
4- Now make a second step on the calculator at 20l and it will give you a cell count. All you have to do is save it and write the count on the container or divide it into containers that match the count you need for the next pitch.

All pretty simple math and yes I sniffed this out after I got the lab set up to count and stain.

 

[Berube05734]

Ok, so say that I'm using "yeastcalculator.com" and input my initial yeast calculation, i.e. initial cell count / production date = viable cell count to begin with.

Initial yeast propagation:

• Fermentation type / Batch Volume / OG = 211B
• Imperial A38 - cell count = 200B
• Production Date = 8/1/22
• Viable Cell Count = 178B
• 2L starter - total cells at finish = 428 B (178B + 250B new cells generated)
• I just need 211B, so I'll retain approx. 50% of the yeast (211*100/428=49%)

Second yeast propagation:

• My retained cell count is approx. 217B
• Production Date = 10/1/22
• Viable Cell count = 193B
• 2L starter provides me with 447B cells
• I take what I need and retain the remaining

and so on and so on...

Is it reasonable to assume that if I agitate the starter into a slurry that I can accurately measure how much to pitch and retain just by separation of volume or liquid weight?

And, I'll just need to be mindful of always keeping track of my remaining number of cells each time.

thx,

 

[Berube05734]

Ok, so say that I'm using "yeastcalculator.com" and input my initial yeast calculation, i.e. initial cell count / production date = viable cell count to begin with.

Initial yeast propagation:

• Fermentation type / Batch Volume / OG = 211B
• Imperial A38 - cell count = 200B
• Production Date = 8/1/22
• Viable Cell Count = 178B
• 2L starter - total cells at finish = 428 B (178B + 250B new cells generated)
• I just need 211B, so I'll retain approx. 50% of the yeast (211*100/428=49%)

Second yeast propagation:

• My retained cell count is approx. 217B
• Production Date = 10/1/22
• Viable Cell count = 193B
• 2L starter provides me with 447B cells
• I take what I need and retain the remaining

and so on and so on...

Is it reasonable to assume that if I agitate the starter into a slurry that I can accurately measure how much to pitch and retain just by separation of volume or liquid weight?

And, I'll just need to be mindful of always keeping track of my remaining number of cells each time.

thx,

VikeMan's method of determining # of cells based on the thickness of the slurry would definitely be applicable (and likely the only way unless you had a mini-lab set up) to estimate the number of viable cells if the beginning number of yeast cells wasn't known.

 

[hottpeper13]

I think as long as you only decant clear(I mean read thru clear) beer off the overbuild you should have very close to what you put in there from the whole.
Let me just say that my method gives me 4 hr lag times and clean tasty beer.

 

[InspectorJon]

Let’s complicate this a bit. I have yeast slurry in the refrigerator that is a year old. The calculators say it’s dead . I don’t believe that because I have resurrected “dead” yeast. If it’s really old I start with a 250 ml, 1.020 small starter step to get it going. Then pitch that into a 1 liter, 1.040 starter. Is there a theoretical maximum yeast density/count for that 1 liter starter?

Using this method is it reasonable to assume that the 1 liter starter would have the same or at least a similar number of cells no matter if I start with 5k, 50k, 500k or 5 million cells in the small first starter?

 

[SanPancho]

the problem with following vikeman's slurry method is twofold. its not like sach are uniform throughout the wine/beer world. the cell sizes vary, and therefore making an assumption on slurry density is really making two assumptions: assuming your strain's size is the "average" size, and then assuming you're making the right estimation on how dense your slurry has gotten.

the second problem gets easier once you've used the strain a few times, and you can see its compacted as much as it will go.

the first problem isnt easy. especially on homebrew level. because the way its done correctly is cell counting. the next best is weighing it. the yeast labs can tell you the density and/or the weight you should be pitching. when you're filling a 1/2bbl keg its easy. but with homebrew level amounts of yeast im not sure that would be practical.

 

[lablover]

I go with a much simpler count. I scoop a half a ziploc sandwich bag of yeast off the top of my nice healthy fermentations about day two. I repeat for about four generations then I use a new pack or two of dry yeast. But, I'm a simpleton for sure....

 

[hottpeper13]

When working with old saved overbuilds I use a sterilized loop to snag some from the middle and put in 15 ml sterilized 1.030 wort screw top tubes. Shake every so often and in 3 days or so sediment will form and foam on top. Pitch into 150 ml of 1.030-1.040 wort,when done pitch enough wort to get to 1500 ml,pitch this into 5 gal of wort. I have no idea of the cell count but the fermentations take off and make great beer.