The problem with mint is that if you go too much, you really know it! This is why I made a mint extract and added the extract to my bottling bucket so that I could taste it as I added. This will help ensure that you do not add too much, but also helps ensure you get the amount you want.
The mint extract does take a while though. I think I had mine soaking in vodka for at least 3 months, but it was taken out of our garden.
I added it into a porter, which I did 3 ways. Bottled some as the standard porter. Then added some mint extract until I thought it had the taste that I wanted, then bottled that. Then I added some chocolate extract that I had soaking in bourbon for about a month, added this to taste as well. Worked out really well!!!