Day 205

Having an accurate idea of how many yeast cells you are pitching into your wort–and what percentage is alive–is pretty important. In Microbiology Lab today, we learned how to count yeast.

If you had to count all the yeast cells in a yeast slurry, it would take you a while, since there are usually several million yeast cells in one droplet. To make the counting job easier, the usual procedure is to dilute the slurry, then look at a very small but defined volume of it under a microscope, then do some math.

We didn’t have a yeast slurry handy, so we took a 1 mL sample of a lager fermenting in the Teaching Brewery, then added 9 mL of water, thus diluting it 1:10. By taking a 1 mL sample of that solution and adding 9 mL of water again, we ended up with a 1:100 dilution of the original beer.

In order to tell which yeast cells were viable and which were not, we added a drop of methylene blue to the final dilution. This turns dead cells blue, but yeast cells that are alive and kicking don’t allow the dye to enter their cells walls and remain clear.

Haemocytometer

A haemocytometer. The dark squares are the five used for counting. The small dots are yeast cells.

Using a very small capillary pipette, we transferred a tiny amount to a special microscopic slide called a haemocytometer.  This slide has a covered section of 25 tiny cross-hatched squares with a volume of 100 nanolitres (a millionth of a litre, or 1/10,000th of a mL). Looking through a microscope, we could clearly see live and dead yeast cells within the 25 squares.

Although counting all the yeast cells in all 25 squares would be easier than counting all the yeast cells in a droplet of original beer, it would still be tedious work. To improve the lives of lab technicians everywhere, the scientific world has developed a protocol of only counting the cells inside one-fifth of the squares–the four corner squares and the middle square–then multiplying the results by 5 to arrive at a reasonably accurate average for all 25 squares.

When I counted by this method, I tallied 19 viable yeast cells and 10 dead cells in the five sample squares. To arrive at the number of viable cells per mL of our original fermenting beer:

  1. I multiplied the 19 viable cells x 5 to arrive at the total cells in the haemocytometer = 95.
  2. Since the volume of the haemocytometer was 1/10,000 of a mL, I multiplied 95 cells x  10,000 to get the number of cells in 1 mL of our solution = 950,000 cells.
  3. Since we had diluted the original beer by 100, I multiplied 950,000 cells x 100 to arrive at a yeast cell count of 95 million yeast cells per mL of fermenting beer.

However, since we had counted 10 dead cells, our percentage of viable cells was only 66%.

On to Packaging, where we had our fourth “Fun Quiz”. Then it was on to the bottling line. Apparently fillers are fairly temperamental machines, so once you have your filler going and it is in a happy place, it’s a good idea to keep it going if possible. So if your labeller suddenly starts firing labels in every direction, a well-designed packaging line can allow the filler to continue to placidly fill bottles, which then can be accumulated in a holding pattern while you quickly adjust the labeller and get it restarted.

We also looked at dealing with broken bottles on the packaging line, and soaker/washer machines that automatically clean and sanitize bottles inside and out.

Normally fascinating stuff, I’m sure, but the Easter long weekend was calling, and when Doug Pengelly ended a few minutes early, the classroom emptied with amazing speed.

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One Comment on “Day 205”

  1. Jason Koebel Says:

    I’m living vicariously through you and your brewmaster journey. I just wanted you to know that. Keep up the good work!


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