Initial population in a yeast starter

[mayflychucker]

Can someone please explain to me the difference between the populations of yeast in two starters if the original (pitched) populations are different?
Example:
In order to save a little money on yeast, I'll sometimes use a smackpack to make a 1L starter for Batch 1 and immediately after pitching, I'll use the 'dregs' left in my starter vessel to get another 1L starter going for Batch 2. I try to eyeball the amount of leftover 'dregs' yeast so it'll be close to the volume in the original smackpack but, of course, this is imprecise at best.
Anyway, I'm wondering if it matters how much yeast you start a starter with. My understanding is that they'll build their population to capacity no matter how many yeast cells were in the original population. Is this true? If so, are there stressors that will affect their viability if under/over pitched in the starter vessel?
Thanks.

 

[Pappers_]

My understanding is that they'll build their population to capacity no matter how many yeast cells were in the original population. Is this true?

No, it is not true. The number of cells grown is dependent upon the ratio of the amount of yeast pitched into the starter to the volume of the wort used in the starter.

There is a section in the Yeast book by Chris White and Jamil Z. about this, with charts that show the exact ratios and relationships between amount of yeast pitched, starter wort volume, and amount of new cells grown. I don't know them off the top of my head, but do remember that if you pitch A number of cells into 1 liter of wort and 2(A) number of cells into 1 liter of wort, the latter will produce more new cells. But not twice as many.

 

[mayflychucker]

Hmmm.
Sounds like I need a new book.
Thanks a ton.

 

[marcycaulkins]

I've come across a similar chart in the Palmer book, and my sticking point is this... if I'm using washed yeast from a mason jar, how do I know how much yeast I'm starting with? Any thoughts?

 

[MachineShopBrewing]

I've come across a similar chart in the Palmer book, and my sticking point is this... if I'm using washed yeast from a mason jar, how do I know how much yeast I'm starting with? Any thoughts?

Estimation and experience, or get a microscope and a hemocytometer. IIRC a white labs vial is 35 ml and contains roughly 100B cells. Use the size of that slurry to estimate what you have in the jar. Be sure to take into account that your slurry is most likely not as pure and compacted as the WL slurry.

 

[rjwhite41]

I've come across a similar chart in the Palmer book, and my sticking point is this... if I'm using washed yeast from a mason jar, how do I know how much yeast I'm starting with? Any thoughts?

Without a microscope you don't really know but you can use the age of the washed yeast and the mrmalty calculator to get a rough estimate. Your yeast is not near as pure or viable (depending on the age of your washed yeast and the vial) as a white labs vial.