It really wasn't so light. I buy from a local roaster, usually by country of origin rather than roast color. This was Brazilian.the last one I made had a green pepper flavor/aroma to some people. Drew suggests using a darker roast to prevent this in cold steeped beer.
I've read this posted a couple times lately. I've never had this issue - yet. My go to is usually Sumatra because I love the earthy, cedary aroma and flavor. The other two beans I really like in beer are Espresso and French roasts, being obviously deeply roasted. What coffee did you have this issue with, out of curiosity? It seems like a really lightly roasted coffee like Kona or Blue Mountain would be pretty susceptible to this issue.
I got the same thing from New Guinea coffee, which my local roaster was not surprised by. I gave him a bottle on Saturday, so I'll have to bug him for tasting notes.
I do coarse cracked beans added to the beer for 24 -48 hours. Volume of beans is kinda up to you. I think I went with 3 oz. for 5 gallons last time.