Dr. Fischborn and Dr. Waldrop: Some time ago I was counting cells and then looked at the datasheets for Windsor and Nottingham and it says (among other things) :

Nottingham contains >= 5 billion viable cells / g(dw)
Windsor contains >= 7 billion viable cells / g(dw)

This got me curious. I have come up with two interpretations of this, either that the Nottingham cells are simply bigger and you only get so many into a gram, or the Nottingham strain are more sensitive to the drying process in the sense that you get a little bit more dead cells per gram.

1) Can you explain why there are more Windsor cells/g than Nottingham cells?
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)

3) I have tried to determine the glycogen contents of yeast slurry, by means of taking a digital picture of the iodine stained cells, and then translate the colour scale into a relative glycogen value (0-100%). Just looking at the colour resolution I think it might be realistic to resolve the glycogen level to maybe 4 intervals, 0-25%, 25-50%, 50-75%, 75-100%.

What do you think about this? Is the correlation between intensity of the staining and glycogen level good? These are one of the few the relatively simple methods that does seem practical for any homebrewer with a microscope and interest since you don't need any hard-to-get chemicals or other lab equipment. The question is, is it reliable for ballpark estimates of glycogen? (provide the camera exponation settings are the same)

In my firsts tests the glycogen drop I arrived at seemed to make sense. It dropped from the 75-100% range to the 25-50% in two days starving at room temp in a closed bottle (noO2). Does this make sense to you?

The pics are actually from a way outdated pack of Windsor that I had saved for experiments. The low glycogen, left is the outdate pack. The right picture is how the outdated pack looks like after

getting a little bit of sugar to eat. Once the sugar finished and two days later at room temp (still on under the beer) the level had dropped significantly judging from the colour.

- Fredrik

RESPONSE:

Fredrik- Yes, Nottingham yeast has usually larger cells than Windsor yeast and Lager yeast has even larger cells than the Nottingham. 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.

As for the glycogen pictures you showed, this is quite interesting and there have been attempts in the past to use image analysis in such a way. Using the level of glycogen in this manner is quite simple but perhaps the scale you are using may be a bit confusing or misleading. I believe you may want to recalibrate your scale. Glycogen can be analyzed in the yeast but I would guess you could reduce your scale by a factor of 2.5 and you may not be too far off. Certainly brewing yeast have been known to accumulate up to 40% glycogen.

Regards,
Forbes & Tobias