Is my yeast starter infected?

[judasegg]

I did a step up starter (500ml to 2ltr) and left the erlenmeyer loosely covered in the fridge, wondering if it is infected. Its from a smack pack...I kept a bit of the smack pack in a sample jar, and it looks as expected (spent wort, white yeast, offwhite trub)...but the starter I made has this dark layer, and I'm not seeing a thin layer of yeast. The 2nd starter kicked off in about 6hrs...please see attached pic

[Waffty]

I'm only just starting out with experimenting with different yeasts, so I'm no expert. That said, when I've made a good starter, it always smells and tastes ok and when something has gone wrong, the smell and the taste reflect this.

Your dark band could just be a thin layer of break material/trub, as from my limited experiences something that has gone off, rarely drops into neat layers.

When I'm messing with yeast, I've taken to using a pressure cooker to cook my glassware etc and I even put my wort in there too, in a kilner jar, with a loose'ish lid, same for my slopes. I also make my starter wort with around 25 IBU of bittering hops and around 1.030 to 1.030 OG. With the hops in there, I find it easier to do the taste test, plus the alpha acids, also help to reduce any infections.

Sorry I can't help more and fingers crossed.