Wednesday, January 9, 2013

How Many Cells Are In A Package?

White Labs and Wyeast advertise 100 billion cells per container.  Fermentlist advertises a minimum of 6 billion cells per gram (69 billion total cells) at time of packaging.

To better understand the yeast pitched, over the last several weeks I have been doing cell counts on yeast purchased from the local home brew store.

Viable cell count
Brettanomyces Bruxellensis
102 billion
Cry Havoc
93 billion
American Ale
77 billion *
153 billion **

* rehydrated in cold water for about 5 minutes, then stirred in.
** rehydrated in 77°F water for 30 minutes, then stirred in.

These three yeast cover a very wide range of yeasts: both liquid and dry,  brewers and wild strains.  There was very little actual content in the WLP650 vial compared to what you might expect with a typical brewers strain.  Microscope examination showed that the cellar morphology of these two are very different.  The WLP862 looks like a typical brewers yeast: spherical and 15-20 micrometers in diameter.  The WLP650 was football shaped, although there was some variation in cell shape.  They also appear to be much smaller at  about 7 microns in diameter and about 10 microns long.

The US-05 looks like typical brewers yeast.  I was surprised that the viability was so low.  This might be due to the rehydration method deviating from the manufactures recommendations.  Although this is not a problem as the viable cell count is high enough.


  1. How did you rehydate the packet of US05, and how old was the packet? I've often heard that US04 and US05 packets contain roughly 200-220billion cells. Your numbers seem to be much more in line with the low-end number that Fermentis lists.

    These numbers will definitely influence my use of dry yeast.

    1. Yes, I was surprised by how low it was as well.

      The packet of yeast was marked "use by 04 2014" so the yeast has over a year before the shelf life expires. To rehydrate the yeast it was sprinkled on top of tap water which was about 60 degrees. The water temperature was low and I mixed the yeast into the water after about 5-10 minutes instead of waiting.

      I'm actually going to be re-hydrating some dry yeast (T-58) this afternoon. This time I'm going to use 150ml of sterile wort at 80 degrees F and leave it for 30 minutes as recommended on the data sheet.

    2. Ya, that is pretty surprising. I've heard re-hydration temperature can have an impact on viability; I know the oft-cited temp range is around 90-105F. Please share the results from the higher temp rehydration!

      Excellent post by the way.

    3. Thanks! Good idea. I'll do four different temperatures by mixing cool and warm wort. I'll shoot for 70, 80, 90 and 100.

    4. It looks more like 150 billion cells and 70% viability when re hydrated closer to the manufactures specifications. I'll write it up in a whole post later, but I would recommend using approximately 90 degree water as the temperature will drop over the 30 minutes.

    5. Wow, big difference. 100% more viability from 30* higher temp. That's much less foolproof than dry yeast get credit for

  2. I'm not certain that the higher viability was entirely the result of the higher temperature, it may have also been influenced by the time the yeast was floating. I'm still looking at the data, and not sure if it will be conclusive. However, the best results were from using a container with a large surface area, such as a cereal bowl. This allows the yeast to float for longer before it absorbs enough water to sink. Also, if you pre heat the container with hot water for 10-15 minutes it will hold temperature better. Then add 90 degree water and sprinkle the yeast on top. Let it sit for 30 minutes before stirring it in.

  3. Thank you for conducting these experiments and sharing your results.

    Just one question: Are you sprinkling the yeast onto 90 degree water, or onto 90 degree sterile wort?

    1. Good question, that could use to be clarified. In one of the replies above I mentioned wort, but I opted to use water instead as water seems to be more common.