Starter method to grow/store yeast

I have a smack pack of Rogue Pacman that is about 4 months old.

I want to use it in an IPA (1.070) and save some of the yeast for a future batch. Here's what I was thinking of doing...does this violate any of the yeast rules/methods?

Method:
2 Liter starter on stir plate....then chill decant most of beer and pour some of the yeast into a sanitized whitelab vial for storage.

then...remainder of yeast in 1 liter starter on stirplate...chill...decant and do a 2 liter starter on the stirplate.

Is this a workable approach?

That would work, but sounds needlessly complicated. I would probably just make one starter, then follow normal yeast washing procedure when fermentation is complete to save some for future batches.

I thought washing yeast from a 1.060 or greater beer (in this case 1.070) was a bad idea due to the yeast being stressed and possibly mutated for future batches?

I do something similar to what you suggested in the OP. I'll make a 2L starter and let it go for three days on a stir plate until I've built up a healthy population of yeast. Then put it in the fridge overnight and decant most all the beer the next day. I'll pour about 4 oz. of the slurry in a sanitized vial or jar to save for next time and pitch the rest of the starter on brew day. If I'm making a bigger beer, like 1.070 or higher, then I might step up with another liter beforehand but not necessarily and depending on what yeast I'm using (for example, I might step up off the slurry for a DIPA using a CA Ale strain, but I wouldn't worry about it using a French Saison yeast since it's such an attenuative beast).

Personally, I like harvesting yeast for future batches from the starter flask much more than the carboy for several reasons: it's easier to pour some yeast out of a flask than it is a big carboy; the yeast is cleaner (not much trub or hop matter) in the starter; and if you use 1.040-1.050 starter wort, then you have less to worry about with regard to yeast mutations (even though, I'mm less concerned about this last part).

I honestly don't think there's much of a benefit between what the OP is proposing vs. washing the yeast after fermentation. Unless he's using Pacman again within a week or two of racking of the yeast cake, he'll still need (or should at least) to make a starter. So, 2 starters vs. 2 starters... Not seeing how one way is better. Personally, I like propagating multiple cultures out of one initial pack of yeast if I'm planning on brewing a higher gravity beer, so I'd go with what the OP's plan. Now if he was brewing something with a gravity of 1.035, I'd recommend just going ahead and washing the yeast from there. And still make a starter with that washed yeast.

Yeah, phenry, there's not much difference between the two approaches. For me, it's easier to pour some yeast from the starter to save for another day, than it is to go through the yeast washing procedure. Generally speaking, with healthy yeast, a 2L starter is big enough to pull off a White Lab's vial worth for a future brew without having to step up and add another liter of starter wort. Pacman strain tends to be a workhorse, too, although for my palette I think it's better suited for the maltier recipes than the hoppy ones...

After making your first 2L starter, your yeast is going to be in high gear. I would suggest that you pour off half or more of your slurry for storage, and then just do another 2L starter (skip the intermediate 1L). I did this recently (2L and 2L) and had my first ever starter overflow. The 2nd starter completely fermented out in < 24 hours.

If you were to pour off from the starter to store instead of washing, would you need to add pre boiled/cooled water to the jar to keep headspace at a minimum? I'm new to starters but I'm all about cutting costs.

Voodoo Child, I figure that keeping headspace down to a minimum is a good idea but I use small enough containers where I don't have to add water. The White Lab vials are great to reuse but the glass baby food jars are also awesome (if you have access to them) because they can also be boiled to sanitize them before use. Mason jars with ring lids are a good choice, too, but then you;ll likely need to step up with another 2L as airving mentioned to be sure you have enough yeast to ferment your batch.

Keeping your own yeast is a great way to save money. I haven't bought yeast in a some time, and you can build a surprising collection from stepping up bottle-conditioned beers--actually, that's how I got my first strain of Pacman going...