Wyeast MFg Date July 1st

Ingredients
1

Hello

I just got one Wyeast Yeast and it says Mfg July 1st 2020.

How much percentage is lost per month? is there a calculator for this?  PLease note its a Smack Pack.

Thanks

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3

what does it mean Mfg + 0.5 ??

so the viability of my yeast is 64% only! 54 days old :frowning:

4

I used to get all hung up on viability numbers (predicted by brewing software) with various yeasts that I have used.  I don’t worry about that anymore.  Obviously I try to use it by the manufacturer’s “best by date” as a precaution.  However, if you make a starter, you will be fine.  I have had some yeast that was almost three months old, made a starter, and had active fermentation in about 4-6 hours.  Denny posted a while back that he made a beer with a yeast that was 2.5 years old just to see what would happen and it came out fine.
With dry yeast they can be a year or so old and they will still be fine.  And no, I do not rehydrate them

5

Not enough to worry about in that short time.

6

Like Mark has pointed out many times, it’s about yeast health, not cell count.

7

I used a 6-7 month old smack pack of WY1450 that the calculators told me had 0% viability.  It fermented just fine.

I would say that if you smack the pack and it blows up, your’e good to go.

8

Yep.  That’s the purpose of a smack pack.

9

I just fermented a mild with Munton’s yeast dated 11/16 that turned out fine. I didn’t rehydrate or aerate.

10

I use the starter calculator in Beersmith.  I understand that this calculator uses a combination of the following to calculate the needed starter size:

  • Mfg date of of the liquid yeast.
    -Brew date
    -OG
  • May be some other factors

I believe that the software estimates that the viable yeast cells diminish by about 20% per month.

I plan ahead so my LHBS can have available Wyeast packs that have been manufactured within 2 months of my brew day.  So far, this has worked well for me.

11

Please throw the yeast cell calculators out with the trash, as they are next to worthless. There is absolutely no way to calculate the viability of a yeast culture and anyone who tells you that you can does not know what he/she is talking about. Yeast cultures are a heck of a lot more robust than most brewers believe. My whole beef with brewing software is that it attempts to achieve a level of precision that does represent reality. The only way to determine viability is to count viable cells using a microscope and a hemocytometer.

In practice, it is never a good idea to pitch a liquid culture that is more than a week or two old without first making a starter. Making a starter is not so much about increasing cell count, as it is about increasing cell health. The yeast biomass grows at a rate of 2^n, where the symbol “^” denotes raised to power of; therefore, it does not take very long for for a small number of yeast cells to become a very large number of yeast cells. What is important is sanitation because bacteria also grows exponentially and its replication period is 1/3rd that of yeast; therefore, the bacteria biomass grows by a factor of 8 every time the yeast cell count doubles.