I like to cook a cabage, and then eat it over a period of a week or
two. But sometimes--and it seems like not always--it will turn sour.
It doesn't look bad or anything, but it's still trash to me. Is there
a way to keep it from turning sour?

Also, I like to boil some potatoes and have some of them around for a
week or two as well, but sometimes they go bad during that time. It
seems like they should keep for at least two weeks in the
refrigerator, and sometimes they do. Why not other times?

Thanks for any help!