I noticed that some raspberries are very tasty and sour but others taste sweet (which I don't like), and it is hard for me to know which it is by looking at them. Their size seem to correlate with this so I try to get small raspberries, but this does not always work.
I heard that the ones that taste sweet are usually a refined species, and that wild raspberries taste better.
I wonder if there is some raspberry kind that is known to be sour. Maybe I can try to remember their name and look in that case.