The taste that is not sweet, like a lemon or a vinegar.
Some people like sournesses, but some people don't.
Examples:
The lemonade has a lot of sournesses.
I don't like the sournesses of this candy.
She doesn't like the sournesses of the apple.
The sournesses of the pickle made her face funny.
The sournesses of the lemon made my mouth pucker.
The sournesses of the vinegar was so strong, it made me shiver.