Reminded of our shamenet to cream cheese procedure back in the early years of our marriage. For some reason, our cream cheese tasted off after a day, and within three days it had all the colors in it. (We used strainer bags, no socks or shorts or whatnot to blame this on.)
I don't know why it took a while but I eventually figured out the problem. DW kept all sorts of old containers - including cottage cheese - which she would wash out with soap and hot water and then store in the closet. It seems that even though the cottage cheese container was washed out with soap and stored for months, the enzymes retained enough potency to accelerate the process in the cream cheese, growing mold within three days.
Conclusion: when Chazal tell you that you cannot kasher a Beis Seor for Pesach, believe them.