I set out to prepare the yeast starter for this brew as usual, boiling up and then chilling DME 2.5 days before the brew day, but I couldn’t get the magnetic stir bar to operate consistently and found that it wanted to jump out toward the edge of the flask all the time, leaving the starter inanimate.
1.5 days after pitching I decided to make another starter in my second flask, this time picking a different stir bar on the basis that my usual go-to bar may have become differently magnetised or otherwise worn out. I did note that the old one lacked the small ridge around the middle, which made for a larger contact area with the base of the flask and therefore increased the amount of friction. Was that enough to upset the apple cart once the viscosity started to change?
Following a successful trial in water using a smaller, ridged stir bar I sanitised it and deployed it to my second starter, where it performed flawlessly for just over 24 hours until pitching, at which point a decent head of Krausen was observed.
#wisdom: the ridge is there to help the stir bar move more easily. Always use a bar with a ridge. 1.5 days seems fine for Lallemand Koln (Kölsch) yeast, ignore the funky packaging / rehydration instructions and prepare starter as usual, observing temperature suggestions.
It’s not without irony then that this brew, Bernsdorfer TTZ, is as difficult to start as the ETZ 250 after which it’s named.