I have been on 4 month brewing hiatus. I have about 6 mason jars full of yeast of different varieties. according to Mr.Malty , I would need to pitch 700ml of 4 month old yeast into a 1.080 og. How does this translate if I am going to make starter? The calculator states 10 percent viability. So at that viability rate, could I assume about 70 ml of live yeast and just build my starter from that?
I’ll give my opinion, but I am no expert. 700mL of 10% viable yeast seems like you would be pitching a lot of dead yeast. I would take maybe two tablespoons of yeast and step it up at least twice for a 1.050 beer, probably three times for 1.080. It may be easier to just buy some new yeast. If you do decide to step it up go easy on that yeast the first round with maybe a 500mL of 1.025 wort. Also with each step, up the gravity and size of your starter for maximum growth.
Sounds to me, that at that point you might as well buy a new yeast pack. The cost of the DME you’ll be using and the time and labor you’ll be putting into it might not be worth the effort of spending $6 on new healthy, viable yeast. Your call though.
I would actually estimate your viability at approx. 25% if stored in the fridge under beer the whole time. Should be easy enough to step it up for a batch. Depending on the thickness of your slurry, I would start with 60-70ml of thick yeast and step it up from there.