Below is a picture of the top of our fermenting stout.
We fermented this at 18c (64f) for 1 week (ambient room temp) and then I let the temp rise to 20c and then 21c over the course of 3 days. There was a thin layer of krausen on top when I started the temp rise. I give it a taste prior to the temp rise, and it was delicious. Yesterday I saw "this" and it gave me a bit of worry. I will taste it again tonight, but figured I would throw the pic out to see what your thoughts are on it.
Thanks in advance for your insight.