Why are my hazelnuts/filberts bitter? I live in the Mid-Atlantic area and have terrible luck buying raw hazelnuts/filberts in the store. They are often bitter and/or old-tasting, very expensive, and you'd never want to eat them raw. 

Last fall, my dad shared some hazelnuts a West Virginia woman gave him straight from her trees as a thank you. It was like eating a completely different nut: chewy, sweet, no aftertaste. These weren't the wild variety, sometimes called "beaked"; they looked exactly like what I buy in the store, just a little smaller. I've read that commercial "raw" hazelnuts may have to be pasteurized before sale. Could this be affecting the flavor of the store-bought nuts? Anyone got a better source than roaming the West Virginia hills (as lovely as that sounds)? My chocolate hazelnut biscotti and I thank you :)

CLARIFICATION (based on the kind and thorough replies to date): The store-bought hazelnuts are often bitter even after I remove the skins, and I'd like to avoid roasting and/or peeling. (I want to make some raw hazelnut flour for a pastry crust, for example.) I will look for the DuChilly variety, however, and welcome thoughts on other varietals. Thank you!
Diarylheptanoids were recently identified as responsible for bitter off-flavor in hazelnuts. This correlates with


infection with bugs (of the bush, not in storage) and
starting germination 


according to: 
Singldinger: Molecular-sensory studies on the development of a bitter off-taste in hazelnuts, PhD thesis, 2019, Munich Technical University. 

Here's also a paper: Singldinger et al.: The Cyclic Diarylheptanoid Asadanin as the Main Contributor to the Bitter Off-Taste in Hazelnuts (Corylus avellana L.), J Agric Food Chem. 2017