This Octoberfest turned out Awesome using WLP830 German Lager Yeast (2 packs) and a strong Diacetyl Rest.
After 30 days at 50 deg F and then 2-3 days at 65 deg F did the trick.
The Carboy was noticeably fermenting during the Diacetyl Rest.
On my first attempt at an IPL I believe resulted in too much Diacetyl off flavors.
On that earlier batch I used WLP940 Mexican Lager Yeast (2 packs).
My local grain supply store has been really lazy lately not stocking the yeast I need...
Surely I screwed up the Diacetyl rest on that 1st batch. The beer is drinkable.
"Diacetyl (also called 2,3-butanedione) is a chemical that has been used to give butter-like and other flavors to food products, including popcorn."