Cold Crashing - Amount of Yeast in Suspension

[Bottoms_Up]

After making a yeast starter, one option is to cold crash the starter, decant and pitch. There seems to be little agreement on how long the starter should be "cold crashed", which also depends on the size of the starter. For a typical 2-liter starter, I've seen recommendations to "cold crash" from overnight to approximately two days. I know from experience, that the starter is still cloudy for up to about 15 days in the fridge.

My questions is: for a typical, say, 2-liter starter, is there any data available as to approximately how much yeast (%) is still in suspension for periods of time (say by each half-day or day) after the starter has been refrigerated?

I'm trying to determine generally what the optimum amount of time in the refrigerator would be best for cold crashing.

 

[ram5ey]

You will be able to tell visually as the liquid on top will be clear. For ales I just pitch the whole thing if it's less than 1500ml.

 

[Gameface]

After making a yeast starter, one option is to cold crash the starter, decant and pitch. There seems to be little agreement on how long the starter should be "cold crashed", which also depends on the size of the starter. For a typical 2-liter starter, I've seen recommendations to "cold crash" from overnight to approximately two days. I know from experience, that the starter is still cloudy for up to about 15 days in the fridge.

My questions is: for a typical, say, 2-liter starter, is there any data available as to approximately how much yeast (%) is still in suspension for periods of time (say by each half-day or day) after the starter has been refrigerated?

I'm trying to determine generally what the optimum amount of time in the refrigerator would be best for cold crashing.

I doubt anyone has the number you're looking for referenced and ready to go.

One thing I have heard is that the yeast still remaining after most have settled out are the yeast that don't flocculate well and will not clear well in your finished beer, so best dump them out anyway. Don't need them reproducing.

I wonder at what point the viability of the yeast already at the bottom decreases faster than new viable yeast settle out?

 

[Bottoms_Up]

You will be able to tell visually as the liquid on top will be clear. For ales I just pitch the whole thing if it's less than 1500ml.

The problem is that the liquid on top is not completely clear until it has been in the fridge for about 15 days, even though it looks relatively clear after a day or two. The amount of yeast in suspension decreases rapidly at first, and then slows down at a declining rate. I was wondering, by percentage, how much yeast is still in suspension, say after a half day, a day, two days, etc.

 

[ram5ey]

Not enough to notice I'm sure

 

[Bottoms_Up]

I doubt anyone has the number you're looking for referenced and ready to go.

One thing I have heard is that the yeast still remaining after most have settled out are the yeast that don't flocculate well and will not clear well in your finished beer, so best dump them out anyway. Don't need them reproducing.

I wonder at what point the viability of the yeast already at the bottom decreases faster than new viable yeast settle out?

Good points, and I have yet to see solid arguments for what the optimal time in the fridge would be. I suspect that leaving the starter in the fridge only overnight would result in a significant amount of yeast still in suspension, which could affect the calculated amount of yeast needed, especially with lagers. I have never seen this reduction of yeast cells mentioned when calculating optimum yeast counts in a starter needed for a specific beer.

Out of curiosity, how long would you leave the starter in the fridge before decanting?

 

[Gameface]

Good points, and I have yet to see solid arguments for what the optimal time in the fridge would be. I suspect that leaving the starter in the fridge only overnight would result in a significant amount of yeast still in suspension, which could affect the calculated amount of yeast needed, especially with lagers. I have never seen this reduction of yeast cells mentioned when calculating optimum yeast counts in a starter needed for a specific beer.

Out of curiosity, how long would you leave the starter in the fridge before decanting?

I leave the starter in the fridge anywhere from 24hrs to three weeks.

I'd suggest not focusing too much on the minutia. Starter size calculations are estimates based on estimates based on estimates. I say get a good number, aim a little high and relax. If all other variables are good (aeration, ferm temp, etc) then you're golden even if you're optimal cell count and what you pitched is a few billion yeast cells different.

 

[Bottoms_Up]

I'd suggest not focusing too much on the minutia. Starter size calculations are estimates based on estimates based on estimates. I say get a good number, aim a little high and relax. If all other variables are good (aeration, ferm temp, etc) then you're golden even if you're optimal cell count and what you pitched is a few billion yeast cells different.

True, I'm not too worried about the results (negligible differences), but the other thing about brewing that interests me tremendously is the math behind it all. I have never purchased a brewing program, preferring to write all my own formulas for most of the process. That way I know a little more about the science behind it all. Maximizing results mathematically/statistically, and adjusting by observation is a real passion that, for me, adds greatly to the hobby.

 

[Gameface]

True, I'm not too worried about the results (negligible differences), but the other thing about brewing that interests me tremendously is the math behind it all. I have never purchased a brewing program, preferring to write all my own formulas for most of the process. That way I know a little more about the science behind it all. Maximizing results mathematically/statistically, and adjusting by observation is a real passion that, for me, adds greatly to the hobby.

In that case I'd suggest getting a microscope and doing cell counts and you will be able to inform all of us how many yeast cells are in suspension given a certain amount of time. There are a select few around here who truly do scientific experiments that answer these questions. We can use as many as we can get.

 

[Yooper]

It is yeast strain dependent. I'm surprised your starters are cloudy for 15 days(!) as even a lager yeast should drop out pretty well by then, but some strains (like Wyeast 1007) are almost non-flocculant and the beer won't clear well without filtration. Of course, hefeweizen yeast strains are the same way.

Most American ale yeast strains are medium in flocculation, while most English strains are highly flocculant, and those should clear in about 3 days or so after finishing up and being kept cold (34-40 degrees) without moving.

 

[Bottoms_Up]

In that case I'd suggest getting a microscope and doing cell counts and you will be able to inform all of us how many yeast cells are in suspension given a certain amount of time. There are a select few around here who truly do scientific experiments that answer these questions. We can use as many as we can get.

I've been considering that possibility. It should be quite instructional.

 

[Bottoms_Up]

It is yeast strain dependent. I'm surprised your starters are cloudy for 15 days(!) as even a lager yeast should drop out pretty well by then, but some strains (like Wyeast 1007) are almost non-flocculant and the beer won't clear well without filtration. Of course, hefeweizen yeast strains are the same way.

Most American ale yeast strains are medium in flocculation, while most English strains are highly flocculant, and those should clear in about 3 days or so after finishing up and being kept cold (34-40 degrees) without moving.

Perhaps "cloudy" is not the best adjective to use. The starter can look quite clear after a few days, but if you compare a 3-day starter directly to a 15-day starter, you will see a significant difference in clarity.