How do I know how much yeast slurry to use?

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kombat

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I've been trying to get into washing and re-using my yeast, but there's still one aspect of it that confuses me: How do I know how much yeast is in that Mason jar in the fridge?

A few weeks ago, I brewed an Oktoberfest using WLP820 (Oktoberfest/Marzen) yeast. After 9 days fermenting, I did a 4 day d-rest, then cold-crashed it. A week later, I racked it to a keg to lager (and get it off the yeast). I washed and saved the yeast in 3 Mason jars. That was 2 weeks ago.

I would like to re-use this yeast to do a Rauchbier. I would like to just decant the clear liquid, warm the slurry to room temperature, and pitch it (as opposed to doing a starter, then cold-crashing and decanting). My problem is, I have no idea how much yeast I have in these jars. I mean, I can see it obviously, and I could measure it by volume, but given that it's been in the fridge for 2 weeks, what's its viability? How much of it is trub? Heck, even if I know the volume, how do I know how many cells that represents without knowing the density of the slurry/yeast cake?

I'd be willing to do a starter if it would result in a clear answer. I basically need 400 billion cells. If I pitch all 3 jars (the entire yeast cake collected from the Oktoberfest batch), I'm pretty sure that'd be an overpitch, but that's still preferable to underpitching, isn't it? My current plan is to just pitch 2 jars, but that's still just a wild guess.

How can I improve my process here and bring some sort of accuracy to my yeast cell counts when re-using yeast like this?
 
what size mason jars? this is a cold, slow fermenting yeast so i'd use lots of yeast, not the whole cake though. there are yeast calculators that will give you an estimate of how much yeast is in the slurry, it's a lot of yeast. the whole point of saving yeast for me is to avoid making a starter and 2 weeks in the fridge is nothing, i've used jars of yeast that were months old and they started fermenting without unusual lag times.
 
Without a microscope, you really are never going to know.

What you can do is estimate. Calculators can do that. You can also do that with your own knowledge.

eg if you are used to making starters, you should know about how much space x number of cells take up in your flask. If you use a calculator to get you in the ballpark and then rely on your experience with your equipment, you should be able to get relatively close to your target.
 
I've been trying to get into washing and re-using my yeast, but there's still one aspect of it that confuses me: How do I know how much yeast is in that Mason jar in the fridge?

..... I washed and saved the yeast in 3 Mason jars. That was 2 weeks ago.

I would like to re-use this yeast to do a Rauchbier. I would like to just decant the clear liquid, warm the slurry to room temperature, and pitch it (as opposed to doing a starter, then cold-crashing and decanting). My problem is, I have no idea how much yeast I have in these jars. I mean, I can see it obviously, and I could measure it by volume, but given that it's been in the fridge for 2 weeks, what's its viability? How much of it is trub? Heck, even if I know the volume, how do I know how many cells that represents without knowing the density of the slurry/yeast cake?

I'd be willing to do a starter if it would result in a clear answer. I basically need 400 billion cells. If I pitch all 3 jars (the entire yeast cake collected from the Oktoberfest batch), I'm pretty sure that'd be an overpitch, but that's still preferable to underpitching, isn't it? My current plan is to just pitch 2 jars, but that's still just a wild guess.

How can I improve my process here and bring some sort of accuracy to my yeast cell counts when re-using yeast like this?

You can estimate the volume of yeast you have in a jar by putting same amount of liquid in another like jar and then measuring it.
Depending on how effectively you have rinsed the yeast it is likely you will have around 2 - 3 bn cells per ml of compacted yeast in the jar.

So for example if you washed the yeast very well and had 50ml of yeast then you could estimate you have around 50 x 3bn = 150bn cells.
If you were less careful and the sample shows some discoloration from trub then go for a lesser density of around 2bn per ml (50ml x 2bn = 100bn cells)

Now how many of those cells are viable depends on age since fermentation was completed. When you input the harvest date for the yeast into Yeastcalc it will estimate how many viable cells you have and guide you to making a starter if required.
 
If you were less careful and the sample shows some discoloration from trub then go for a lesser density of around 2bn per ml (50ml x 2bn = 100bn cells)
Or if you can tell that you have roughly 50% yeast and 50% trub, then just multiply that times the 2-3 billion cells/ml to tell you how much yeast you have.

So if you have 100 ml total, but you can tell it's only 50% yeast, then you'd have 50 ml of yeast.
 
Or if you can tell that you have roughly 50% yeast and 50% trub, then just multiply that times the 2-3 billion cells/ml to tell you how much yeast you have.

So if you have 100 ml total, but you can tell it's only 50% yeast, then you'd have 50 ml of yeast.

Wyeast has an explanation about harvesting yeast on their website. This is basically what they say, too. They say that if you have 40-60% solids, then there are ~1.2 billion cells per ml.

But I assume that is with fresh yeast, and it degrades over time. They also say to use it within 2 weeks, and I know others say it will keep longer. Yeastcalc includes the date in its calculations.

Seems like you should underestimate the viability, since it seems generally worse to underpitch than to overpitch?
 
Wyeast has an explanation about harvesting yeast on their website. This is basically what they say, too. They say that if you have 40-60% solids, then there are ~1.2 billion cells per ml.

Wyeast figures seem to give some credence to my estimate of 2-3 bn cells per ml which is based on the solids only and assumes the yeast has been carefully washed fairly clean of impurities.
The overall number of cells in the jar will not diminish with age but the number of viable (live) cells will. That is where Yeastcalc will estimate how many good cells you still have.

Most of my reading supports what has been already stated that it is better to err on the side of over-pitching a little rather than under-pitching.
 
Sorry I don't know the answer to that. There is conflicting information out there. I've been using the 0.7% reduction in viability because I'd rather over pitch than under pitch.
 
To be sure I understand, viability isn't a big deal in a month?

There are differing views on rate of viability decline with aging and that is to be expected I guess when dealing with so many variables. I would expect different yeast strains would exhibit differing rates of viability decline.

I think the easiest is to settle on some formula or calculator and always use that to estimate number of viable cells for you. I shall continue to put my faith in Yeastcalc until it can be shown to be unreliable.
 
what size mason jars? this is a cold, slow fermenting yeast so i'd use lots of yeast, not the whole cake though. there are yeast calculators that will give you an estimate of how much yeast is in the slurry, it's a lot of yeast. the whole point of saving yeast for me is to avoid making a starter and 2 weeks in the fridge is nothing, i've used jars of yeast that were months old and they started fermenting without unusual lag times.

So many people on here harp on doing a starter esp if re-pitching, but this is a pain in my arse...you may have just pushed me over the edge to not doing a starter with my washed yeast next time!! Do you overpitch due to no starter? And is your technique to just let it warm to room temp prior to pitching? Do you let it warm in its native "juices" then decant and pitch, or decant and let warm then pitch?
 
I usually top crop over wash, so it's usually no trub and all yeast. That being said, i've direct pitched jars of top cropped yeast that are within a month old with no problems all the time. I recently just scooped some slurry into a sanitized jar, stuck it in the fridge, pulled it out on brew day and pitched that directly into my fermentor. Had activity within hours. That was with 2 week old slurry!
 
So many people on here harp on doing a starter esp if re-pitching, but this is a pain in my arse...you may have just pushed me over the edge to not doing a starter with my washed yeast next time!! Do you overpitch due to no starter? And is your technique to just let it warm to room temp prior to pitching? Do you let it warm in its native "juices" then decant and pitch, or decant and let warm then pitch?

most of the beer i brew is in the 4-5% ABV and on my system i know that 10lb of grain will get me an OG of 1.050-1.055. over time i've settled on 1/4 cup of unwashed slurry as the sweet spot. i do let it warm to room temp before pouring into a sanitized measuring 1/4 cup. the yeast left in the jar i throw away since the beer i just pitched will provide yeast for subsequent batches. i used to keep lots of jars of yeast around but i only keep 1 or 2 of any one kind.
 
I don't bother washing, no starters, just jar it up and use about half a quart mason jar per 5 gallon batch. I have used several month old yeast with no issues other than an extra day to start really cooking along. I keep my own yeast bank of everything I brew with.
 
Same as a few other here, I dont wash the yeast but jar the whole yeast cake and stick it in the fridge. When brewing a new batch I pitch half of the previous cake, works fine and the beer tastes great which is all that matters in the end right?
 
I only have one jar of each yeast I use. From that, I propagate a starter for each batch. My method may not be right, but it works for me and I can keep my batches consistent this way. I use this calculator as a starting point: http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

For the most part, I brew approximately 4.5 g batches around 1.055 OG. Assuming that each step maxes out at 6x yeast multiplication. I start with 1/4 tsp of yeast (approximately 1.2 billion) and 9 oz of starter for the first step. Second step is 1.25 qts of starter. When this second step slurry is ready, I decant, and pitch 2-3 liters of the wort into the starter. My fresh wort goes into the fridge to chill overnight. The next afternoon, I will pull the wort from the fridge and let it warm towards room temp. When the wort hits 60 degrees, I pitch the whole starter.

This is only an estimate, but I assume I'm pitching at a rate of .75 ml/*P. It works great. Sometimes if the next batch is using the same yeast, I'll pitch the new wort right on top of the last cake without washing.
 
I only have one jar of each yeast I use. From that, I propagate a starter for each batch. My method may not be right, but it works for me and I can keep my batches consistent this way. I use this calculator as a starting point: http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

For the most part, I brew approximately 4.5 g batches around 1.055 OG. Assuming that each step maxes out at 6x yeast multiplication. I start with 1/4 tsp of yeast (approximately 1.2 billion) and 9 oz of starter for the first step. Second step is 1.25 qts of starter. When this second step slurry is ready, I decant, and pitch 2-3 liters of the wort into the starter. My fresh wort goes into the fridge to chill overnight. The next afternoon, I will pull the wort from the fridge and let it warm towards room temp. When the wort hits 60 degrees, I pitch the whole starter.

This is only an estimate, but I assume I'm pitching at a rate of .75 ml/*P. It works great. Sometimes if the next batch is using the same yeast, I'll pitch the new wort right on top of the last cake without washing.

that's a lot of steps but if it works that's great. i would not expect that pitching on a whole yeast cake would make the best beer, in fact i'm pretty sure it wouldn't.
 
Would it, though?

Wouldn't I still have to know how much yeast I was pitching into the starter in order to have any idea how much I'll get out of it?

Im a server at a large brewery and when I use their yeast, I use about a cup per 5 gallon batch. Thats with it being 99% viable. And your not going to know how viable your slurry is unless you dilute it and count the yeast cells, like the big boys do for each batch.

But you dont have to be exact. The pro brewers tell me that unless you severely underpitch, or severely over pitch (more than 3x), you won't have off flavors.
 
that's a lot of steps but if it works that's great. i would not expect that pitching on a whole yeast cake would make the best beer, in fact i'm pretty sure it wouldn't.
Yes, it is a lot of steps, but I always have the same amount consistent to each batch. This way I know I have a lot of viable yeast. If I use only slurry, it may not be enough viable cells.

I only "sometimes" pitch on the last cake. The last batch I did this was a porter on top of an IPA. It had a little bit of tartness that I think came from the large dose of hops. I won't do that again for different batches. Several others in this thread also said they pitch on the old cake with no problems.
 
When I buy a new strain I make 2x the starter I need and hold back half. So I start every batch from a 12oz jar with 1/4" of yeast sediment on the bottom and step it up to 1L over 3-4 days.
I've had luck with this technique so far and been able to use WY1028 that's been stored under boiled water in the fridge for 8-9 months.
I'll probably have to get a new vial eventually but I'm 3-4 batches in and the yeast seem happy.
 
You can estimate the volume of yeast you have in a jar by putting same amount of liquid in another like jar and then measuring it.
Depending on how effectively you have rinsed the yeast it is likely you will have around 2 - 3 bn cells per ml of compacted yeast in the jar.

So for example if you washed the yeast very well and had 50ml of yeast then you could estimate you have around 50 x 3bn = 150bn cells.
If you were less careful and the sample shows some discoloration from trub then go for a lesser density of around 2bn per ml (50ml x 2bn = 100bn cells)

Now how many of those cells are viable depends on age since fermentation was completed. When you input the harvest date for the yeast into Yeastcalc it will estimate how many viable cells you have and guide you to making a starter if required.
Following this advise I filled a jar with an amount of water that was close to the amour of yeast in same size jar. Turned out it was 10ml of water. I think my yeast is washed pretty well so assuming 10ml of yeast, am I'm looking at only 20-30 billion cells in that jar before factoring in harvest date?
 
Buy a microscope.
Buy a hemacytometer (slide that is used for counting cells).
Figure out your ratio of viable cells to volume of fluid in the sample (literally by counting under the microscope).
Utilize any one of the numerous free pitching rate calculators available online which typically only require you to put in a few basic pieces of data you should already be logging every time you brew as well as have logged ahead of time on your brew sheets.
Do some basic math to figure out what volume of your slurry you need using the total number of cells needed based off the pitching rate calculator in relation to the average number of living/viable cells you found doing the cell count in your new microscope.

Without a microscope there are way too many variables to know exactly how many viable cells you have in one of your jars of slurry. If you do not wish to or are unable to for any reason purchase a microscope then you have two options:
1. Email your local community college. I bet they have a lab and a student would be happy to do a quick cell count for you (maybe offer them a sixer of homebrew for their time, if they are 21+ of course).
2. Drastically over pitch. Its better then under pitching, doesn't require you to buy a microscope, and will have no negative impact on your final beer.

I have a lot of commercial brewing experience and the general rule of thumb (for facilities without a proper lab of course) is "when in doubt, over pitch"

I also am fully convinced that autolysis does not exist. I worked at a brewery that left a belgian dark strong ale, at around 9% abv, on a 5th or 6th generation repitch of wyeast 1762 belgian abbey II for over 3 months at 70f (no, none of that was a typo) and that was the cleanest belgian style ale that ever came out of that facility.
 
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