I've made a couple black walnut beers. The first one was a black walnut porter that was phenomenal. I used way too many nuts though so it came out tasting strangely like a barley wine, strong, fruity, and bitter. I cut down on the nuts the second time and came up with something I really like. This time I did an ESB, very similar to that pecan recipe posted since I used Maris Otter malt and a very small amount of hops. I recommend toasting as well since this will allow for less oils and give a more robust, nutty flavor.
The first time I did this I used so many nuts that there was a thin layer of oil on top of the fermentation tank! This was easily avoided with my transfer tube so unless you're pouring into a bottling tank it's no problem. One of my friends drank the dregs on a dare. He said it wasn't bad but I wasn't about to touch that goop.
I didn't get any oil, however, when I cut down to .5 lbs per 5 gallon batch. Roast the nuts till they're light brown but don't get them too dark otherwise they'll lose their flavor. I do a taste test myself (they're delicious roasted by themselves!) to decide when the flavor is right.
The flavor is strong enough you have to make the recipe around it. I reduced the hop quantity to about 3/4 oz. You end up with a fruity, nutty accent to the beer with enough bitterness to not notice the loss of hops. Don't trust your initial reactions. Both batches took over a month for the taste to mature. The nut taste gets more powerful and more fruity as it ages. I've found optimal length is between 2-3 months bottle fermentation time to allow the flavor to mature.
My next step will be to make a black walnut IPA. I think if I combine the bitterness of the nuts with a good hop mixture I'll get an incredibly complex IPA. I hope others try this as well. Black walnuts are a great way of blowing your fellow brewers' minds! I found some at
www.nutsonline.com and
www.black-walnuts.com. Hammons Products sells them in grocery stores and Wal-Mart too but some places don't have them.