I have been making homemade yogurt with my sous vide for months. Today after 18 hours of cooking it has green mold sitting on top of it, what the heck happened? Any ideas? I use organic whole milk, I heat it to 180 degrees, I cool it to < 115 degrees and ad about ¼ cup of my previous yogurt and then let it process at 108 degrees for 12-24 hours. I just checked it and there is mold growing on the surface of the yogurt.