How is starter size calculated?

I've seen the calculators and such, but I'm trying to figure out how they come up with the volume they do. I understand the first part of wanting to pitch proportionally to the density of sugars and the volume the yeast will be spread through and that the 0.75 constant for ales and 1.5 constant for lagers represents the ideal workload for each cell.

I don't understand how to go from the number of cells you want and the number you have in your packet, to the volume of starter needed. I'm guessing that since your starter gravity is optimized at 1.040 or so, you choose the volume that gives the yeast enough sugar to divide the appropriate number of times and then restock its reserves for dormancy. But how much sugar per cell per division does that take?

 

I can't really say. I know JZ did a lot of work on his calculator and worked with Chris White in doing so. You could probably figure from his numbers something reasonable. He also has some calculations on his site. In general you want to get within 20% of optimal yeast count so you have a large margin of error that will still yield excellent results. If you want more accurate data you might post this on the science thread to get the attention of the more technically minded folks.

 

I'll give that a try. Thanks for the suggestion.

 

look no further than mr. malty for your calc needs: http://www.mrmalty.com/calc/calc.html

 

Well I don't know what JZ or Pallmer uses to compute pitching rates, or what their cult followers may beleve. I've never read or lstened to their stuff. But I do know what American craft brewers consider as an appropriate pitching rate: 1 million cells per ml per degree plato. European brewers think that is too high, but it seems to work for Americans. They seem to sell a bunch of good beer. Here's an example: Suppose your wort was say 1.060, or approx. 15 plato. Then you need 1 million x 15 = 15 million cells per ml. Since 5 gallon is about 19,000 ml, you now need (15 x 10^6 ) x (19 x 10^3) = 285 x 10^9 cells. Since one ml of good slurry has about 1x 10^9 cells (this is an approximation given by White), then you need about 285 ml of good slurry. That is about 1/3 quart of thick yeast. I only get about half that from a 4 liter starter, but it seems to do the job. Maybe the Europens are right, the Americans are overpitching. Anyway, that's how you compute pitching rates. Easy-Peasy...

 

Instead of throwing insults across peoples' bow based off admitted ignorance maybe take a minute to see what folks are doing. JZ's calculator goes off .75 million cells per ml per degree plato. JZ did a good job with that tool, had expert advice, worked hard and tested it extensively...that is why many people use it.

 

Sorry you perceived my response as an insult to anyone. I simply said ( in so many words) it is so easy to figure pitch rates "a caveman could do it". And personally, I'd just as soon remain ignorant of what JZ and JP are doing because I really don't care one way or another....

 

That's just the Sudsy charm we've all come to know and love...

 

Thanks. No reason you have to listen to them, but no reason to disrespect the amount of work they have done to help others out. I appreciate anyone taking the time to put good information forward. I have gained from your and many others' posts here on TBN through the years along with JZ, countless scientific journals, books, etc...if its good info, I'm all ears personally.

 

I think I will throw some poop in the game. Do you propagate your yeast aerobically or anaerobically, and how do you do it. What is the Crabtree Effect? ---bobz

 

billybrew.com recently did a nice piece on stepping up starters. He developed a nice chart from JZ's "Yeast" to show the # of cells in a 1 - 5 L starter. The graph is for starters without a stirbar as that creates a larger number of cells.

http://billybrew.com/stepping-up-a-yeast-starter