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Thread: Dry yeast cell count (US-05)

  1. #1
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    Dry yeast cell count (US-05)

    There seems to be much disagreement on the number of yeast cells in dry yeast. Mrmalty claims it is as high as 20 billion cells/gram, while other resources suggests it is only half the amount. Manufacturers stay on the safe side, and states that it is +6 billions cells/gram. I use 10 billion cells/gram in my calculations, but if 20 is correct, i could use half the amount of yeast. Are there any recent studies to support that it is as high as 20 billion cells/gram? I use Safale US-05 as my house yeast.

  2. #2
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    I've never used dry yeast commercially, but I prefer it over liquid yeast for homebrewing when appropriate strains are available. Back when I was brewing at home a lot more often, assuming 20 billion viable cells per gram gave me inconsistent fermentations. I then read somewhere (and don't remember where) that dry yeast is often in the ballpark of 20 billion cells at 70% viability. Once I switched my assumption to 14 billion viable cells per gram, my fermentations became very reliable. The manufacturer values are guaranteed minimums, so the actual counts should be higher than 6 billion.

    Hopefully someone who's actually done a bunch of cell counts and viability tests on dry yeasts will chime in. If I ever remember to do it when things aren't crazy at the brewery, I'll report back.

  3. #3
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    Dry Yeast Cell Counting

    Quote Originally Posted by jwalts View Post
    I've never used dry yeast commercially, but I prefer it over liquid yeast for homebrewing when appropriate strains are available. Back when I was brewing at home a lot more often, assuming 20 billion viable cells per gram gave me inconsistent fermentations. I then read somewhere (and don't remember where) that dry yeast is often in the ballpark of 20 billion cells at 70% viability. Once I switched my assumption to 14 billion viable cells per gram, my fermentations became very reliable. The manufacturer values are guaranteed minimums, so the actual counts should be higher than 6 billion.

    Hopefully someone who's actually done a bunch of cell counts and viability tests on dry yeasts will chime in. If I ever remember to do it when things aren't crazy at the brewery, I'll report back.
    Hey jwalts, have you had a chance to revisit this?

    I am looking very closely at my yeast now that I have started counting cells and this question is one I’m trying to find answers to.

    Have you tried dry yeast in your brewery yet?
    Last edited by A-Frame Brewing; 12-14-2019 at 08:15 PM. Reason: Grammar

  4. #4
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    This thread is almost three years old...there is plenty of information on the cell counts of dry yeasts available from the yeast manufacturers. Dry yeast is commonly used in commercial operations, as is liquid yeast cultures. Pitch rates vary on a number of factors. Counts will vary by strain sometimes, and viability can be affected by hydration methods among other factors. Liquid has more strain variations available but dry is usually cheaper. They both produce award winning quality products when used properly.

    Homogenization of samples is the main reason for discrepancies. You are taking a drop from a tank and extrapolating it out (and that’s after a serial dilution). The propensity for variance is huge. The cell count data needs to be used in conjunction with other information to make proper determinations on yeast activity.

  5. #5
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    For the sake of closing the loop, no, I haven't looked into this any deeper. I've used dry yeast commercially for seltzers (don't judge me; not my call), but it was a wine yeast, and I started with the manufacturer's recommended lb/bbl and adjusted from there in the same unit. It would be easy to figure out the corresponding pitch rate in million cells/mL/P by diluting a given weight of dry yeast and counting the viable cells - and doing it a bunch of times to gauge the consistency - but you may have guessed by now that my heart isn't into the seltzer thing. I agree wholeheartedly with UnFermentable that sampling is a major issue, but that has more to do with repitching than pitching yeast from their purchased packages - which are much easier to homogenize.

  6. #6
    Join Date
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    I can speak to this from a yeast manufacturer's perspective.

    Counting viable cells for dry yeast is actually not a trivial task. The yeast must be rehydrated prior to counting, so the cell wall undergoes a transition from gel to liquid crystal phase. Typical staining methods can give falsely low readings since the cell wall is more permeable during this time. Automated cell counters can be unreliable since freshly rehydrated cells do not necessarily look like typical yeast cells for which the software was optimized. Plating on nutrient agar is a reasonable alternative, but you must assume that each colony corresponds to a single cell. If cells clump together, it will also result in falsely low viability counts. You can reduce clumping by sonication or a quick turn in a blender, but these methods can also reduce viability...

    I have never seen cell counts as high as 20 billion per gram for any dry brewing yeast (Lallemand or otherwise), I would be curious to see the methods used to achieve this. You might see these numbers for baking or wine yeasts where the cells are typically smaller (therefore more per gram), but not for a typical brewing yeast, which is typically 5-10 billion viable cells per gram.

    In the end, I would encourage people to not count cells at all when using dry yeast. Simply pitch by measuring the weight of the yeast, 50-100g/hL for most Lallemand ale strains. Pitch rate calculators designed for liquid yeast using a typical 1 million cells/ml/'P do not work very well for dry yeast and usually result in significant overpitching (3-6x the recommended pitch rate for dry yeast). I have a best practice document available for dry yeast viability and pitch rates, send me a PM and I can send it to you.

    Or check out the Lallemand Pitch Rate Calculator optimized for dry yeast. These pitch rates are validated by test fermentation after each production to assess lag phase, attenuation, total fermentation time and flavor.

    https://www.lallemandbrewing.com/en/...te-calculator/
    Lallemand is a global leader in the development, production and marketing of yeast, bacteria and specialty ingredients.

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