Ive brewed a few Rauchbiers, cold smoked regular two row malt at about 10% of the grist is all you need. I used alder for the smoke, and only smoked the malt for about an hour. That's easy to overdo the smoke if your not careful. I also tried dropping the steaming hot rocks in the wort and adding them back to the secondary for a krausen. It was dangerous, don't recommend that one unless your daring.