I love them dry roasted, preferably unsalted. My grandmother used to buy bags of raw unshelled peanuts (Arachis hypogaea) which we then roasted or boiled. A steaming plateful fresh from the pot is also something I wouldn't refuse.

My grandmother taught me how to choose good legumes. Squeeze them gently to make sure the pods are full. Only mature peanuts will do. Immature pods will taste a bit bitter. I followed her and got it right most of the time. Years later, as a science teacher I taught Freshmen college students about legumes and nitrogen-fixing bacteria but never really looked up nor realised why only mature peanuts are most pleasing to the taste.

Now, research shows that harvest time determines the taste of peanuts. From the Associated Press through Yahoo! News Study: Harvest Time is Critical for Peanuts:

"Harvesting at optimal maturity is extremely important as far as flavor is concerned," said John Beasley, a University of Georgia peanut agronomist and member of the research team. "We know from previous research and from the industry that when immature peanut kernels are processed, they develop a bitter or off-flavor taste."

Aha! So that's why there's very good and sometimes bitterish peanut butter, peanut brittle and what have you.

Well, I still don't know the specific chemical or lack of it that affects the taste of peanuts but the abovementioned study is a good starting point. One of these days I hope to do a bit more sleuthing.

In the meantime, when buying peanuts, do as my grandmother did: gently squeeze and make sure all pods are full.