Yeast Slurry Viability Check

I've got a Wyeast 1056 Slurry from a Porter I brewed at the beginning of last month and I want to check the viability to use in a Stout this weekend.

I've been doing some reading, and, according to Mr. Malty's Yeast Pitching Calculator, I need 391 ml of yeast slurry to pitch for a target OG of 1.070. This comes out to roughly 6 oz and I've decided to make a starter to test this yeast out. I took 1/2 lb of DME and boiled it in 1/2 Gallon of water, then added ~ 6oz of the slurry to it when I got it down to 80 degrees F.

If the yeast seems to be active after a day or so, should I double my starter by decanting the liquid and yeast in suspension into another 1/2 gallon of wort?

I'll be buying a backup smackpack just in case

Any pointers are appreciated.
vinsonizer

 

In my experience, yeast slurry starts really fast and lasts a long time as long as it's pretty watery.

One time I tried a 0.5 gallon starter for a batch instead of a vial. Didn't notice any difference. It was 4 gallons, about 1070 OG.

 

I would suggest you RDWHAHB. You're repitching a proofed yeast slurry after a month. Probably fresher than your smackpack, even!

 

I think it is safe to say that the yeast is still plenty healthy. It was bubbling 2 hours after I pitched the slurry into the starter, so RDWHAHB seems to be perfect advice.