Have you brewed it yet? Curious what you decided on. I brewed an imperial milk stout yesterday, and plan to add coffee, vanilla beans / cacao and peppermint to secondary. I bought some left hand milk stout, and was experimenting with peppermint extract ratios.. . turns out for 8 ounces of beer, 1 teaspoon was kind of the sweet spot.
The thing is, when you do the math to up the ratio for 10 gallons of beer (my volume) it would mean adding 26.6 ounces of peppermint extract! That number scares me! Any input would be great!