Bitter hazelnuts

My Corylus  americana nuts are bitter this year. They don’t seem to have any insect or disease damage. Did I harvest too early? They were starting to turn brown. The shells seem to be full.

Will roasting make them less bitter?

In my experience American hazelnuts are more variable in flavor than European. Were they bitter last year?

Perhaps this is due to a long history of domestication on the European front.