Need some input on yeast cake starting with lower og to higher og

[eluterio]

My intention are to use a yeast cake but need some more info to convince me why I cant dump fresh wort on this specific yeast cake.

I want to brew a batch of low gravity beer starting at 1.030-1.035 and about 3.5-4 gallons. Making the yeast a second generational yeast. From here I want to drop 5.5 gallons of 1.50-1.055 wort onto the yeast cake without washing or rinsing. Here is my dilemma:

1.030 of 4 gallons of wort needs 86 billion cells no need for a starter.
1.035 of 4 gallons of wort needs 100 billions cells potentially no starter.
I read somewhere on here that 1 ml of yeast slury contains about 4.5 billions yeast cells, homebrewtalk forum.

With this said, how many ml are in the yeast cake on average? Also on this forum i have read ther is 4.5 billion yeast cells per 1ml of yeast slury. If there are 100 ml you will have 450 billion cells that is way too much for a starting gravity beer that is 1050-1056. Yet it works with bigger beers as noted below.
So i have recently brewed a lager which takes more then 200 billion cells. Both examples are 5.5 gallons batches and I use Brewersfriend.com yeast calculator to figure all my yeast starters. for a 1.050 lager it requires 387 bill cells. I used this yeast cake for a bigger beer with a starting gravity of 1.066. A 1.066 requires 504 bill cells. Even with the calculation I noted before 1 ml = 450 billion cells. If this is the case and there are 200-300 I would have a estimation of 900-1350 billion cells and would be considered OVER PITCHING. The beer turned out just fine.

Again all these numbers ive pulled off of estimations from brewersfriend and homebrewtalk forums.

Now my questions will I be successful if I use the lower gravity beer to use as a starter and dumped another on top of the yeast cake at a higher starting gravity? I just need some more input any would be appreciated.

 

[1975brewer]

I'm a bit of a haphazard brewer so I'm only giving you my own experience over the last year. To save a little on yeast & for convenience I have been pitching on yeast cakes a lot this year. I have been brewing enough this year that I often have something ready to be racked to a secondary fermenter on the day I'm brewing. I have not had a bad experience yet & the last 1 I did was American ale on top of a yeast cake from a high gravity holiday ale. There was a little hint of the holiday spices in that when I racked that 1 to the secondary but now it is kegged I can no longer taste them. Its not scientific advice but I would do it.

I really like getting 2 beers & only scrubbing the fermenter 1 time.

 

[eluterio]

Thanks 1975brewer!

 

[05m50dan]

So your process is basically correct but there's a few assumptions that you have wrong. The first assumption that you have wrong is that there will be 4.5 billion cells in 1 milliliter of yeast slurry. The yeast density will be different from one strain of yeast to another. Another problem you have you never know how much trub is in any given slurry. Even if you use the same recipe and the same yeast the amount of trub will be different from basketball match at least slightly enough to throw off your calculations. Whoever said there was 4.5 billion yeast cells per ml of slurry didn't really know what they were talking about.
The other issue you have is that you are severely over pitching in your second batch. During the growth phase of yeast the yeast kick out a lot chemical compounds that contribute to beer flavor. When you over pitch with yeast they do not go through the growth phase and you lose all those compounds that would contribute to your beer.
A better process is to use smaller amounts of your yeast slurry in your second batch, and any further batches. What I typically do is to make a 2 to 3 gallon batch of beer that Falls in the1.040-1.050 range. I rack beer off the cake leaving a little beer behind to loosen up the cake. I'll swirl around this remaining beer and pitch 1 cup of this loose slurry into about 5 gallons of regular strength beer. If I'm going to a big beer like barley wine or double IPA or Russian Imperial Stout then I'll use about half of the slurry. Or if I'm going to make a 10 gallon batch I'll use all of it.
Hopefully this helps. This is not to say that you won't make good beer, or even great beer the way you planned to, but this is a better practice.

 

[eluterio]

So your process is basically correct but there's a few assumptions that you have wrong. The first assumption that you have wrong is that there will be 4.5 billion cells in 1 milliliter of yeast slurry. The yeast density will be different from one strain of yeast to another. Another problem you have you never know how much trub is in any given slurry. Even if you use the same recipe and the same yeast the amount of trub will be different from basketball match at least slightly enough to throw off your calculations. Whoever said there was 4.5 billion yeast cells per ml of slurry didn't really know what they were talking about.
The other issue you have is that you are severely over pitching in your second batch. During the growth phase of yeast the yeast kick out a lot chemical compounds that contribute to beer flavor. When you over pitch with yeast they do not go through the growth phase and you lose all those compounds that would contribute to your beer.
A better process is to use smaller amounts of your yeast slurry in your second batch, and any further batches. What I typically do is to make a 2 to 3 gallon batch of beer that Falls in the1.040-1.050 range. I rack beer off the cake leaving a little beer behind to loosen up the cake. I'll swirl around this remaining beer and pitch 1 cup of this loose slurry into about 5 gallons of regular strength beer. If I'm going to a big beer like barley wine or double IPA or Russian Imperial Stout then I'll use about half of the slurry. Or if I'm going to make a 10 gallon batch I'll use all of it.
Hopefully this helps. This is not to say that you won't make good beer, or even great beer the way you planned to, but this is a better practice.

Thank you for the clarification. I used some of the facts from this website to build my assumption.

From what I here you saying about over pitching on second batch I understand now.

Overall it seems i may have to invest into more Carboys.

 

[eluterio]

So your process is basically correct but there's a few assumptions that you have wrong. The first assumption that you have wrong is that there will be 4.5 billion cells in 1 milliliter of yeast slurry. The yeast density will be different from one strain of yeast to another. Another problem you have you never know how much trub is in any given slurry. Even if you use the same recipe and the same yeast the amount of trub will be different from basketball match at least slightly enough to throw off your calculations. Whoever said there was 4.5 billion yeast cells per ml of slurry didn't really know what they were talking about.
The other issue you have is that you are severely over pitching in your second batch. During the growth phase of yeast the yeast kick out a lot chemical compounds that contribute to beer flavor. When you over pitch with yeast they do not go through the growth phase and you lose all those compounds that would contribute to your beer.
A better process is to use smaller amounts of your yeast slurry in your second batch, and any further batches. What I typically do is to make a 2 to 3 gallon batch of beer that Falls in the1.040-1.050 range. I rack beer off the cake leaving a little beer behind to loosen up the cake. I'll swirl around this remaining beer and pitch 1 cup of this loose slurry into about 5 gallons of regular strength beer. If I'm going to a big beer like barley wine or double IPA or Russian Imperial Stout then I'll use about half of the slurry. Or if I'm going to make a 10 gallon batch I'll use all of it.
Hopefully this helps. This is not to say that you won't make good beer, or even great beer the way you planned to, but this is a better practice.

Thank you for the clarification. I used some of the facts from this website to build my assumption.

From what I here you saying about over pitching on second batch I understand now.

Overall it seems i may have to invest into more Carboys.