[trentmark]

I don't use dry yeast very much, and am using it for an apple ale this weekend- using s-04.

seems like much variability in consensus of cell count per gram of dry yeast. for my 1.050 apple ale, target pitch is 185BB. 2 packs of s-04 at 6BB (manufacturer count) would require me to pitch 31g or almost 3 packs.

are the  manufacturers estimates solid or should i use higher average cell count per gram?

Here's a link that explains the difference in counts:http://www.danstaryeast.com/articles/cell-count-and-glycogen

To summarize, Danstar (and perhaps other dry yeast companies) use plate counts to determine the number of  live cells. Plate counts are reliable to determine live cells because dead cell won't grow. The problem is that it is impossible to plate single cells consistently because they tend to stick together. So when counting what appears to be colonies formed from a single cell, often two or more cells formed that colony. According to Danstar, "For Nottingham yeast the average cell count under the microscope is around 20 to 30 billion cells per gram dry yeast." That leaves it to us to determine viability.

[S. cerevisiae]

One term that one will hear/read in discussions involving plating for single-cell isolates is morphology.   Morphology refers to the shape of a colony.  It's usually fairly easy to determine if colony was formed by more than one cell.  A multicell colony goes out-of-round fairly early in the growth process. 

[archstanton]

I don't use dry yeast very much, and am using it for an apple ale this weekend- using s-04.

seems like much variability in consensus of cell count per gram of dry yeast. for my 1.050 apple ale, target pitch is 185BB. 2 packs of s-04 at 6BB (manufacturer count) would require me to pitch 31g or almost 3 packs.

are the  manufacturers estimates solid or should i use higher average cell count per gram?

Here's a link that explains the difference in counts:http://www.danstaryeast.com/articles/cell-count-and-glycogen

To summarize, Danstar (and perhaps other dry yeast companies) use plate counts to determine the number of  live cells. Plate counts are reliable to determine live cells because dead cell won't grow. The problem is that it is impossible to plate single cells consistently because they tend to stick together. So when counting what appears to be colonies formed from a single cell, often two or more cells formed that colony. According to Danstar, "For Nottingham yeast the average cell count under the microscope is around 20 to 30 billion cells per gram dry yeast." That leaves it to us to determine viability.

Nice find. So the manufacturers numbers are based on a far more accurate means of counting cells. While they agree with what is seen under a microscope, it is not an accurate representation of the actual number of viable cells, rather far from it.