Best before is advice, use by means use by

Best before June 1989
Best before June 1989

My wife was making a carrot cake at the weekend. When she went to use the baking powder, she found it was 3 months out of date and threw it out. We had just come back from the supermarket, but forgot to pick up some more. I offered to ask our retired neighbours for a teaspoon. They very kindly invited me in whilst they had a look whilst telling me it’s been a while since they had done any baking. Out of their flavouring and colours tray came this old looking ‘Butterwicks’ [I think] backing powder. I accepted the packet but thought I’d better check the ‘best before’ stamp – June 1989! That’s 20 years passed it best before date. Twenty years!

We got the other one out of the bin. Cheers though, good cake.