Viable Cells: dry vs liquid

[Blitzkrieg]

So I keep reading this on HBT that it seems to be common knowledge that an 11.5g pack of dry yeast has approximately double the viable cells of a vial or pack of liquid yeast. Where does this come from? A pack of US-05 (arguably one of the most popular dry yeast strains) ships from the lab with just 69 billion cells. Now I realize that the dry yeast will store better and stay closer to that 69 billion than a liquid would, but when I do my starter calculations with reasonably fresh yeast I always have more than 69 billion viable cells to start. Are we assuming that liquid yeast is always months old and therefore less than 34 billion cells? I'm intrigued...

 

[mtnagel]

Good question. MrMalty.com will tell you there is about 220 billion cells per 11.5 g packet, but you are right, when you look up the specs on the fermentis website, there are in fact only 69 billion cells.

 

[Beezer94]

The amounts listed are minimum number of viable cells at packaging. If you look hard enough you can find the resources where people used microscopes to count cells and found significantly more than the minimum.

 

[mtnagel]

Not saying you are wrong, but are you sure about the minimum part? This says typical analysis.

 

[boydster]

Yes, I am sure that 69 billion is a minimum. Fermentis claims the packets are packaged with an average of 150 billion viable cells, and state that 69 billion is a minimum guarantee. The packets say > (greater than) 69 billion cells. It is a guaranteed minimum, so if you have a packet stored at room temp that is about to expire, you still have a baseline that you can expect. Seen experiments with US-05 viability by Sean Terrill for confirmation.

 

[BigFloyd]

An 11g packet of dry yeast, according to microscopic counts, contains somewhere around 220+ billion cells.

From the Q&A on Danstar's website -

Question:
2) Setting aside viability, what is the typical actual total cell count per gram Nottingham?

I did a count some time ago, and though my methods are very crude and homemade (using estimates drop volumes), and may give errors, I arrived at a much higher count, around 20 billion/g. It did only one count, so there may have been error, but I am doubtful that my error is that large, or if the numbers you guarantee are rather on the low side to be safe? I never repeated the experiment so I could have been in error, but it would be nice if you can confirm what is the excepted actual total cell count, rather than the minimum guaranteed viable cell count)

Answer:
The viabilities mentioned on the technical data sheets are minimum viable cells per gram that we guarantee determined by plate count on YPD-agar. Usually the viability is higher. There is a slight difference in how resistant the different strains are to drying and rehydration. Usually ale yeast strains are more resistant than lager yeast strains.

You might also consider that you will find much higher cell numbers under the microscope than by plate count, even if you have 100 % viability because you do not always have a single cell forming a colony but rather two or more cells. For Nottingham yeast the average cell count under the microscope is around 20 to 30 billion cells per gram dry yeast.