Too much yeast? Calc discrepancies

[KYT]

I'm making a small batch imperial red ale: 6 liters OG 1.088
I'm using WLP001 pkg date 03.17.14
I designed the recipe in BeerSmith2
It's in one of those small white buckets, I think it's 2gal-ish.
Stored in the basement at a pretty consistent 18°C
As you may have guessed, I had to replace the airlock twice yesterday and again this morning before work.
BS2 said viability was 95.25% 95.25B cells, and that I should make a 0.48 liter starter or pitch 2 vials.
Today I checked JZ's prc, it says viability is 67% and I should pitch 1.4 vials or make a 1 liter starter.

I'm not opposed to a good, active fermentation, and I don't mind having to replace the airlocks; it's much less work than cleaning sticky from my baseboards. I was planning on letting it sit in the basement for 10days, then bringing it upstairs for the last 4 days for the diacetyl rest (2 weeks total in primary).
What does concern me is, detriment to the finished product from too much yeast, and how much volume am I going to lose to yeast cake?

[Ozwald]

The viability numbers are just wild estimations. There's a lot of variables that neither one of those calcs are taking into account. That being said, JZ's pitching amounts are much more accurate in this case.

As far as the amount of yeast, whether you pitch 1 vial or 3, there's going to be a very similarly sized yeast cake when you're finished. The growth rate will be wildly different which is going to affect the fermentation & the final product. Since the cake is going to be roughly the same size, you're going to lose roughly the same volume either way, which can suck in those smaller batches (proportionally you're losing the same percentage as a larger batch, but smaller units count more in smaller batches - 12 oz is nothing in a 1bbl batch, but is a huge loss in a 1g batch). The best thing you can do to minimize your losses is to tilt your fermenter to let everything settle to a corner & siphon off the opposite corner.

[Afterlab]

I wouldn't worry about a loss of volume from having too much yeast during fermentation. When the yeast settles out it typically creates a pretty tightly packed layer at the bottom of the vessel. If for some reason volume loss does become a problem just start your fermentation with an extra 0.5-1 gallons in a larger vessel so that you're assured of having at least 5 gallons of finished beer to package.

I would always rather have too much healthy yeast than not enough. The main thing I would look out for would be to ensure that there's a proper supply of nutrient for that entire population of yeast. It doesn't do any good if you have a large population of yeast and there are only enough nutrients to supply half of them. The other concern, if you could really even call it that, would be the loss of isomerized alpha acids that attach to the yeast cell walls. The larger the population of yeast, the larger cumulative surface area of yeast cell walls and the larger the percentage of isomerized alpha acid loss. Not the biggest concern for a home brewer but those are the only things I can think of.

[KYT]

The viability numbers are just wild estimations. There's a lot of variables that neither one of those calcs are taking into account. That being said, JZ's pitching amounts are much more accurate in this case.

As far as the amount of yeast, whether you pitch 1 vial or 3, there's going to be a very similarly sized yeast cake when you're finished. The growth rate will be wildly different which is going to affect the fermentation & the final product. Since the cake is going to be roughly the same size, you're going to lose roughly the same volume either way, which can suck in those smaller batches (proportionally you're losing the same percentage as a larger batch, but smaller units count more in smaller batches - 12 oz is nothing in a 1bbl batch, but is a huge loss in a 1g batch). The best thing you can do to minimize your losses is to tilt your fermenter to let everything settle to a corner & siphon off the opposite corner.

WOW I just wouldn't expect the vials to lose 33% viability in just a month. If that's more accurate, then Brad Smith needs to update BS2.
I might be able to adjust viability on it, I'll have to look.

Tilting seems like a good idea. Would I need to stir up the sediment a little for the diacetyl rest and let it resettled tilted? or tilt it now?
Might help with the overfoam if I tilted it now, away from the airlock. Of course now that I've considered that, it'll probably be fine when I get home lol

[KYT]

In BeerSmith2 the default Liquid Age Rate is 21% with a starting viability of 96%
If I use the Yeast Starter tool, it produces a result MUCH closed to JZ's
Viability 68.48% but still 0.54 L starter, not 1 L like JZ's says.
I also found that somehow the package date was set to Apr 25 2014, which was the date I brewed.
I changed it to Mar 17 and the viability dropped to 70%.
It assumes 100 billion cell count, and suggests a 0.69 L starter lol

I'm glad I didn't make JZ's 1L starter, as my 500ml seems to have been way more than enough.

[BeeNtard]

I'm using WLP001 pkg date 03.17.14

Is this the date on the package, or are you taking the date on the package and subtracting 4 months and calling it the packaging date?

[KYT]

Subtracting 4 months. Date stamp says 07.17.14

[Ozwald]

I don't pay attention to those viability numbers at all. They're a wild estimation & could be off by a lot. You're more interested in growth. The only time when it's going to be a major concern is when you're trying to bring back some zombie yeast that has an extremely, extremely low estimated viability.

It's better in most cases to slightly overpitch than to slightly underpitch. A 1L starter is correct, a 500mL starter isn't going to give you much growth at all, even though it looks like you're adding a lot of volume to the fermenter. If you were worried about the extra volume, I would've done a 1L starter, let it finish, decanted off the liquid & pitched the slurry only.

Regarding the tilting, treat it just like any other batch. It's settling into a smaller area, but not by that much, not to mention there's still plenty of yeast in solution that hasn't flocced out yet to take care of diacetyl. Pitch your yeast, use a blowoff tube instead of an airlock, tilt it right away & forget about it until dryhop or bottling day.