I’ve had the most success suspending whole beans in a chilled keg for a couple of days. 2oz in five gallons of a 5.5% beer, but for a RIS you might want more.
The guys from Modern Times did a presentation on brewing with coffee at NHC a couple of years ago, which is where I got the idea of using whole beans. Their talk is definitely worth a listen.
I add cracked whole beans to the keg in a dry hop canister (or fine mesh paint strainer bag) and pull when the flavor is where I like. Generally, a couple days.
My coffee Stout is made with a Cold Brew during bottling. I use Camerons French Roast, Coarse ground. about 1/2 a cup of coffee (usually a bit more) in each 2cup mason jar. let it sit for 48-72 hours. filter into a sterilized larger mason jar (takes quite awhile). add to the 5gal bottling bucket to taste.
I’ve read heat destroys the aromas, and with a coffee that’s really one of the important parts to keep, and it fades quickly. the best part is, if there’s any left i get to drink the cold brew.
Figured I would fill everyone in on the results of my original post in this thread. I ended up going with Rhoobarb’s method of cold steeping. Made 15 gallons and used 3 different types of yeast (separately) in each carboy. Added some really nice vanilla extract and each beer turned out great. Entered it into a comp and it took a gold as well as an honorable mention best of show in the same comp. My only concern was that the body of the beer was slightly compromised due to the amount of coffee water added so I may bump up the base grain next time or try adding whole beans to the boil. Overall it worked it great though.