Strange separation in starter

[Lichtung]

Hey everyone! I've spent the last 2 months not posting to the forums because there is such a wealth of information on the site! Thanks!

I bought some older (October 14/14) Wyeast 1272, American Ale II, for cheap at my LHBS and I planned to use it for an IPA. I made a 2L starter with DME @ 1.036 and let it ferment, on my stir plate, for 1.5 days. I then put it in the fridge with an airlock on it, filled with starsan. It sat there for 1.5 days. During this time I noticed that the level of starsan in the airlock dropped, so I topped it up, assuming some kind of strange fridge evaporation. This happened again and I realized that it's probably not evaporation (ridiculous idea!) but rather that the airlock was leaking starsan into the flask.

Alongside this starsan leak (maybe?) I began to notice a weird separation in the starter; There is a centimeter of creamy liquid sitting on top the starter.

I took a sniff, but it was hard to smell anything. I could just smell CO2 and the rubber bung... I had to pour out my last batch of beer, which was heart breaking, and would rather never have to do that again.

So my question is, is it an infection, or could it be the starsan interacting with the yeast? If so, why does that happen? I couldn't find pictures of this same phenomenon anywhere; this could just mean that it's not a problem and people don't post it!

Lost my camera's battery charger. The photo and all it's gamma nuance is compliments of my laptop computer: sorry...

Thanks one-million in advanced!

 

[LLBeanJ]

That layer is Starsan. It has a lower gravity than the starter wort, so it is floating at the top. Cold crashing the starter caused the pressure to drop inside the flask, which sucked the Starsan out of the airlock and into the starter. Next time, just use sanitized foil to cover your flask while the starter is working and leave it in place for the cold crash. As far as the Starsan in the starter goes, it will be fine. The starter beer's pH has effectively neutralized it. Just be sure to decant the majority of the liquid before pitching.

 

[Lichtung]

Thanks for that, that was really clear! It never occurred to me that the cold crash would create a suction. Cheers!