stringy green beans?

[sheeshshe]

lots on my mind right now LOL! hopefully I'm not bogging down the board!

so, I am trying to figure out if my green beans are super stringy of a variety or if I am just cooking them too long or wrong or something and making them that way. and of course I can't recall the name of them. it was either blue lake or kentucky wonder? they're pole beans. can you cook it worng and make them super stringy?

[garden5]

I'm growing Kentucky wonder and I've found that when I cook them, they are pretty good, but once in a while there will be a stringy one.

How big are they when you harvest them? I've found that the more mature ones tend to be a little on the more-stringy side.