I have used New Belgium's Abbey ale to grow up
a beer starter. It makes good beer. Started by adding
a little unfermented 1.030 wert (like a teaspoon spoon) back
to the carefully poured bottle of commercial beer...then
allowing that time to ferment and begin doubling up wert
additions to pitch volumes....step 2 becomes 2 tbl spoons.
Step three becomes 4...et al...