About 3/4 to 1 ounce coriander per 5 gallons is a good amount to start out with, for a moderate level of orangey citrus flavor. It will start out tasting kind of strong for the first week or two, then mellow out over time. After a couple of months, the coriander fades way out into the background. So, part of figuring out how much to use is knowing how quickly you think you might drink it. If drinking it all fast, then maybe use 3/4 ounce, and if letting it age for a few months, go the full ounce. My opinions. Adjust on future batches if necessary. I add mine in the last 5 minutes of the boil but you might also want to experiment soaking in a little vodka and then adding the flavored vodka to the finished beer a little at a time until it tastes right.