posted 11 years ago
It could be a refrigerator problem.
Unless you empty the refrigerator totally and scrub down every interior surface with bleach, spores will find a place to hide. My refrigerator has a healthy population of blue cheese spores, and any cheese, once it is unsealed from the store-bought bag, will develop a green mold in a few days. I don't mind, because I like blue cheese, but it has become the default cheese for anything left in the fridge for over a week.
I've had that problem with milk that you mention -- open it up and two days later it has soured completely. The way I dealt with that was to start using buttermilk instead of regular milk. When a carton of milk comes home from the store, the first thing I do when I open it is to introduce a sample of buttermilk and let it sit at room temperature for a few hours. Once the buttermilk bacillus has gotten a good head start, there is no competition from other bacteria that would want to sour it in an unusable fashion. I also use buttermilk active cultures to turn half-and-half into sour cream and heavy cream into cream cheese. My ultimate goal is to have penicillium and lactobacillus so naturalized in my fridge that I can set a cup of raw milk into it, come back in a week, and have a cup of buttermilk blue cheese salad dressing.
You have two choices as I see it: (1) realize that your fridge is an ecosystem, just like your garden and cultivate those species which you don't mind and weed out those that are unacceptable or (2) lots of bleach and elbow grease, so that your fridge is barren of any microflora.