Have a starter of approximately 400ml of 1.030 wort that I added the dregs of 2 bottles of rogue dead guy ale to. Approximately .5 - .75" of each bottle. It's been on the stir plate for about 48hrs with no visible indicator of yeast growth. What's the realistic longest I should leave it going before giving up the ghost and figuring theses bottles didn't have any viable yeast (poor handling,storage,old bottles,sun spots or just bad luck)?