Two vials of the same yeast but two different dates

[BoomersBrews]

I am about to make a starter for a DIPA using WLP001. My LHBS only had one vial left so I ordered another to be shipped from Northern Brewer. I'm assuming this second vial will have a slightly different date than the other so I am wondering if anyone has ever used two of the same yeast with two different dates, and if so, how do you go about calculating viability with the two different dates? I'm sure I'll still be fine with the 1.2L starter that I plan to use (along with a stir plate of course), but I'm curious about others' experiences with this viability issue. I tend to be a bit anal with my calculations and I like to measure things perfectly. Cheers!

 

[Qhrumphf]

One of those situations where I'd use Yeast Calc instead of Mr. Malty. Figure out the viability of each, and then add them. If one is 85% viable and one is 60% viable, enter the initial cell count (100% viable) as 145 billion cells.

 

[LLBeanJ]

One of those situations where I'd use Yeast Calc instead of Mr. Malty. Figure out the viability of each, and then add them. If one is 85% viable and one is 60% viable, enter the initial cell count (100% viable) as 145 billion cells.

^^^^ +1

Exact advice I would have given.

 

[BoomersBrews]

One of those situations where I'd use Yeast Calc instead of Mr. Malty. Figure out the viability of each, and then add them. If one is 85% viable and one is 60% viable, enter the initial cell count (100% viable) as 145 billion cells.

I've only ever used Mr. Malty so I was unaware that I could do that with Yeastcalc. I figured there had to be some way to use the mean viability of the two, but I was going to try using Mr. Malty with a date halfway between the two actual dates. Sounds like Yeastcalc will be much more accurate though. Thanks for the good advice!

 

[Qhrumphf]

Each site has its strengths and weaknesses. Yeast Calc is more customizable and has more options (including using different folk's growth curves). But it lacks repitching from slurry, which is usually what I'm doing, so I usually end up using Mr. Malty. But when you need to combine different packs, or make stepped starters, or anything more complicated, Yeast Calc is usually more useful. But for your average simple starter each one will work just fine.

Like I said, enter the date for each individually, note the viability, which assuming WLP or Wyeast packs of 100 billion cells, will conveniently tell you how many billion viables cells are in the pack (75% viable = 75 billion cells). And you can then uncheck the box to calculate by date, set the viability to 100%, and then set the cell count to the total of both packs. I've done it that way in the past. Haven't had to do it often, but it's easy to do.