Damrite said:
Great you answered all my question, except one is the final product the same?
I'm not sure what you mean when you ask, "is the final product the same". My experience is that the yeast ferments the same as it did when I used the smack pack or vial. I only use to four generations. I'm sure if I tried to go further, things would change due to mutations in the yeast. However, I stop at four generations just to be safe.
The math and economics are:
Original yeast costs $7.
I get three canning jars of one pint each.
I make starters, so I save $7 on my next three brews for a total of $21.
Those three brews yield 9 additional one pint canning jars, saving me 9 x $7 = $63.
Those 9 jars yield me 27 one pint canning jars, saving me 27 x $7 = $189.
So, by harvesting yeast I can potentially save $263! I can buy a lot of grain and hops with $263!
If you have a house yeast, then harvesting yeast is a great option, because your using it before you have a lot of dead yeast cells. You'll also be using it quickly.
If you use different yeast strains, then it isn't as economical. You need to use harvested yeast fairly quickly. If not, you'll have a lot of dead yeast cells (see Mr. Hampton's comments in other threads about harvesting yeast and viability. If you don't use it quickly, you may have to only use a portion of the yeast in a particular canning jar to keep the dead yeast cell count down and step your starters. This gets you into using more wort to step your starters, cutting into your savings somewhat.