I've made a pale ale spiced up with coriander, orange and grapefruit peel to ferment together with the beer at the of the fermentation. It was the zest from 2 oranges and 1 grapefruit, I have kegged it now and I am able to test. The taste is very nice, but the head fizzles away directly making a load sound like when you pour champagne or something. Could it be the zest possibly? Or the method I used to add it (directly to the beer), I wanted a extracted flavour and I think I got it. But no head though...