Hi boscar, adding cocoa powder will infuse a cocoa flavour into your stout, how much to add is often a case of trial and error, so for the first attempt don't add too much and you can increase it for future batches. Just bear in mind that if it contains any sugars, either added or naturally, then these sugars will ferment out and add to the alcohol strength.
Dark brews such as stout often go well with dark sugar such as demerara, treacle, etc, so cocoa will be along the same lines of flavour
Comments
Dark brews such as stout often go well with dark sugar such as demerara, treacle, etc, so cocoa will be along the same lines of flavour