I'm familiar with the flavor contribution of rye malt, what does flaked rye contribute in terms of flavor? In a 5 gallon batch, does the amount of flaked rye it would take to add creaminess also cross the flavor contribution threshold (can one taste it)?
I've used rye malt numerous times at average rates of about 40% of the grist. It honestly doesn't have a huge flavor impact, certainly not "spicy" like everyone says. At 15-20% I don't think anyone will really even notice the flavor. However, Denny will be sure to remind me that he thinks it's spicy, and I'm coming to believe that the flavor contribution or lack thereof is largely dependent on which brand is selected.
I have not used flaked rye so I can't really comment on that. I believe it will have a very similar and perhaps even more significant effect, but haven't tested it yet myself.
If you're concerned about "spiciness" (lions and tigers and bears, oh my!) then stay down low at 10-15% where I'm really quite confident that it won't be overpowering at all. Same advice would apply to the malt or the flaked, either way, I would think, with flaked having possibly even more significant impact to body and fullness, not sure about flavors.