Buttermilk is like yoghurt, sour cream, cottage cheese, cream cheese and other cultured products and can be eaten well past their use by date.. Buttermilk also can be used in marinades and curry and anywhere you would use sour cream. It is good in scones , breads and pancakes . My grandfather drank buttermilk ever day . Sadly he died in his 60's but I don't think the buttermilk killed him.
Gert