I add in the last part of the boil too, and usually put the spices in a muslin sack. I sometimes put the sack with the spices right in the primary along with the beer... Also, I think if you have a mortar and pestle, or even a ziploc bag and rolling pin, and lightly crush the coriander seed, it gets to the flavor better.
I brewed a wit the other day and added blood orange peel and meyer lemon peel at flame out. After chilling, I siphoned to my carboy leaving the peel and coriander behind. I'm worried that the peel and coriander didn't have enough contact to really impart flavor. Thoughts?
I would have given them at least 5 minutes, but it also depends on how fast you chill your wort.
On a side note I used dried orange peel once without a hops bag and it took an hour to unclog the spigot, counterflow chiller and racking port on my conical. Those little dried chunks can get pretty big once they hit hot wort.
Because it has been warmer than average, the ground water has already started to heat up and it took about 30 minutes where it usually takes about 15-20 this time of year. I'm sure it will be fine, but I may throw some more peels into the primary after another week or so.
I really like 5 minutes and flameout for those additions. I just did a pale ale that was coriander and orange peel and 5 minutes, then the zest of three different oranges, a tangerine and a grapefruit at flameout.
And yes, crack the coriander, some say that toasting it in a pan is even more helpful in terms of getting the flavor out