Dark ring on top of washed yeast

[Spellman]

I have been washing and reusing yeast for quite some time now with great results. I went to make a starter today and found this dark ring on many of my yeast jars. I am wondering if this is a mold or infection growing or if it is somewhat normal. This one got a bit mixed as I was looking at it, but the others have a more pronounced edge around the jar. It is kind of a purple/black color. I am making this beer for my wedding and decided to get fresh new yeast to be on the safe side. I couldn't find much information on this issue but would really appreciate any help on identifying what it is. I have been saving yeast cakes until now, but have been considering saving a portion of each starter instead in hopes of keeping healthier yeast with a lower chance of infection. Thoughts?

 

[h-bar]

I had the same thing happen about two years ago. I think you made the safe choice of getting new yeast, but maybe there isn't anything wrong at all. At the time, I was less experienced and just dumped it. Now, I'd try to make a starter with it and just observe. If it smells weird or isn't growing at a healthy rate, it's probably no good. If everything seems okay, I'd use it or rewash.

I'd be interested to see if anyone else has experienced this.

 

[Spellman]

I have seen some similar coloring a while back and used with decent results, but it was not as pronounced as this. At the time I wasn't as knowledgeable either and I think I attributed it to being cool just out of the fridge. I have 60 gallons of beer left to make and definitely am not going to risk it at this point. I don't have the time to rebrew so it was a no brainer this time around.

One note I feel I should add is I stored these in the bottom shelf of my fridge. I used to have it at the temp used while it still held food in the kitchen. Now that this is for serving beer and yeast storage, I have since bumped up the temp a few degrees to about 40 for serving. I know this is a little warm for long-term yeast storage, but maybe that temp change is allowing anything else in the wort to gain a foothold. In a perfect world it would be pure yeast and beer filling these jars, but I do not have biology lab to carry these operations out and it would be foolish to think that there aren't any trace amounts of nasties in the air and all around that find their way past the star san sanitizing.