how much coffee to add for a coffee stout

What to give my stout a suttle hit over coffee.  How much should I add for a 5 gallon batch.  And when should I add the coffee?

I've read a clean way to add that flavor is to cold-steep the coffee beans and add just the flavored water, to taste.  I would guess 5 oz to a 5 gal batch is safe for starters; you could always add more later.

5 oz. in a 5 gal batch is not going to give you any real flavor.  I have heard of people who put almost 1 oz. of espresso in every bottle.

I recently made a coffee porter and did it 2 ways.  I "dry beaned" by adding 3oz. (by weight) of coarsely ground, seriously dark roasted beans at flame-out.  I also added 1 1/2 cups of strong brewed to the batch prime syrup before I bottled and this was for a 2.25 gal batch.  I have not yet tasted the product fully conditioned, but the sample I took for the hydrometer tasted quite delicious.  It tasted like a mild cup of black coffee, but not quite as bitter.

The amount also depends on several other factors, like type of beans, how you add them and what your other ingredients are.  Your taste preferences will also be a large factor.  Someone might like the amount in one batch but another might find it overwhelming.

Do a sample test to check how much to use. 4-24 oz should be the range your looking for. Basically put a small measured amount of your beer in a graduated cylinder and do the cold extraction process. Now add some of your  filtered coffee cold extract with a small pipette to the sample and taste untill you find whats right for you. This way you know when you have hit your mark. Now multiply out to figure out how much to add for the whole batch. Remember you can always add more but cant take it out once its in there.

Cold extraction process=
Add .5 lbs of coffee to 24 0z of cold filtered water in a sanitized container. Allow to sit in the fridge for 24 hours. Then run it through a coffee filter. All or part may be added depending on taste.
-from "Radical Brewing" By Randy Mosher.

Good Luck.