Qtde of yeast

Hi,

I have a doubt about the qtde of yeast (number of dry yeast packs).

Supposing that:
Ale with OG 1,085. - 50 liters
Fermentis S-33 - have 69 billion cell by pack

In the "yeast cell needed" recommend 760,9 billion cells, but on "dry yeast recommendation" is 4 pkgs.

To have 760,9 billion cells, I need of 13 pkgs.
If I use only 4 pkgs (as recommended by BS I will have 276 billion cells.

Why I have this difference? What of this values is more effective (yeast cell needed or dry yeast recommendation")?
'
I think that I need to disconsider the "number of pkgs recomended" and use the "yeast cell needed" to calculate the pkgs that I need. 

I searched about my doubts and I have some points to discuss ...

The pack doesn't have exactly 69 billion cells. This number is the minimum cells in the pack in low conditions. I read a lot of diferents numbers of billion cell/g (12, 15, 20). I will use the conservative value 10 billion cells/g.

The difference between yeast cell needed and dry yeast recommendations, because BS use a default value to bi/g by each yeast pack.


Ok, but after some hours reading about pitch rating I have some doubts ...

On brewersfriend calculator, I read about the manufacturing pitching recommended.

"In their defense, the product does contain extremely healthy first generation yeast. One justification might be that the 0.75 rate really applies to pro brewers – who repitch. That re-pitched yeast contains some trub, dead yeast, and other junk, so the 0.75 rate is not as pure as the 0.35 manufacturer’s rate. Repithched yeast can’t be 50% gunk, probably closer to just 10% after washing."

I understood that fresh yeast is good. But if I use a low pichting rate (underpitching) the yeast will longer time to reproduce and can be "stressed"? Why first generation can be used as "underpitching"?

I'm thinking to consider 0.75 or 1.00 as pitch rating (ales below 1.060), it are good values? I think that if use a biggest pitch rating my fermentation will finish quicly and health ... It is right? Or these pitch rating not be consider to first generation?

The items that are going to most affect BeerSmith's calculator are the cell count and the packaging date. After that is the Type choice, then the format (liquid, dry, etc.).

robocop said:

I understood that fresh yeast is good. But if I use a low pitching rate (underpitching) the yeast will longer time to reproduce and can be "stressed"? Why first generation can be used as "underpitching"?

Click to expand...

Simply, yeast is at it's purest and healthiest when it comes directly from the manufacturer. This means no trub or any other source of contamination plus the yeast is very well fed.

Now, that said, it doesn't meant there is always enough cells to get fermentation complete and clean. This means either a starter or buying more yeast. Underpitching isn't an absolute issue. Brewers have so much other control over the health and viability of the yeast in the wort that a little underpitching is fine.

The #1 control that a brewer has is fermentation temperature. Both temperature and pitching rate play a role with esters, fusels, attenuation and a wide range of other flavors.

The second best control is oxygenation of the cool wort. Oxygen has a large role in yeast growth, health, esters, attenuation, fermentation speed and even flocculation.

There's a lot of value in the yeast calculators, but they shouldn't be more than a guideline.  Fundamentally, a brewer should look to pitch a healthy, viable population that needs no more than 3 doublings to be at the optimal rate of 2 million cells per milliliter per degree plato. Anywhere inside that number and you're fine. Most of the calculators are getting you to about 1 million c/ml/P, so that only 1 doubling is needed. Below that number and you're still going to make good beer as long as you have good sanitation.

Repithched yeast can’t be 50% gunk, probably closer to just 10% after washing."

Click to expand...

Brewers Friend is a great site, and I have read this before too.  But it seems like a very weak argument against mfr suggested pitching rates, which is the context.