I am certainly no expert, as I just started working with cultures. To me, frothing sounds like contamination. My ischia culture became contaminated and exhibited the same frothing you mentioned. After another day, it began separating in the jar between feedings. I washed mine per the instrucions from sourdo and within a day or two, it looked much healthier. Now that both cultures are healthy, I realize how bad the contaminated culture smelled. I too didn't think it was bad at first. Now I realize it was the best indicator of contamination. With mine, the entire cooler I was storing them in smelled. Now I have to put my nose down close to the jar to smell it at all and it smells like dough to me. As I understand it, there is no harm in washing your culture beyond the delay in using it. You can always post a photo of the culture to let others help.