Bad milk

This morning the milk in my coffee was bad.

I had just opened the carton of long-life, with a "best by" date suitably far into the future and it tasted of bad cheese and ruined my coffee. This is the second time this has happened in the last couple of weeks. Last time we bought 6 litres of milk (you have to buy milk when you can get it here - there very often isn't any), and they were all bad.