I believe in the 4 - 7 rule. After propagating yeast from slants for years with out a good idea of the number of cells I was pitching, I finally invested in the equipment to count cells. I was not only surprised by the number of cell being cultured but the difference the fold increase made in the yield factor. Below are the data from an increase from a slant to a 4000ml culture. I began by dilution streaking onto an wort-agar plate and selecting 5 good size colonies to inoculate the 10ml culture. The next steps are outlined below. The volume for each step is a total of the wort plus the inoculum from the previous step. For example the 100ml culture was 90ml of wort with the 10ml culture added. You will notice the first step was 10 fold, the next step was 5 fold, and the final step was 8 fold. Also note the yield factor for each step and how the 5 fold increase achieved the greatest yield factor with only a small drop in the 8 fold increase. You may also conjecture from these data that when making a 2 liter starter from liquid yeast we are making 5 or 6 fold increase as the 500 ml culture produced 1.4 billion cells. Please keep in mind there is an error factor (amount unknown to me) when counting with a hemocytometer. So there may not be a significant difference in say 40.7 million and 37.7 million, thereby the yield factor 30.85 may not be significantly different from 33.60. I would guess the other yield factors are different. Sorry about the table format, I could not make the insert button work. I hope it comes through readable.
Culture Cells/ml Total Cells Cell/ml Total Cells Yield Factor
(ml) at Pitch at Pitch at Finish at Finish
10 10,075,000 100,750,000 144,000,000 1,440,000,000 16.75
100 14,400,000 1,440,000,000 194,000,000 19,400,000,000 22.45
500 40,740,000 20,370,000,000 287,500,000 143,750,000,000 30.85
4000 37,734,375 150,937,500,000 306,500,000 1,226,000,000,000 33.60