Twobob;

Holland in their film of their barrel shop have a similar temporary muffle as Alex describes, except that the Holland iron/steel pipe is only about 6-8 inches long, and of course there is a lot of flame that can be seen around such a short pipe-- making it appear as if the barrels are in direct contact with the flame.

However, Verney-Carron uses a direct flame. Their video explains how they do it, but one needs to be fluent in French--I am not.

Regards;
Steve