It's one of the oldest methods of cooking. Dig a hole in the ground, fill it with fire, add a large animal, cover, and cook. Most people recognize it as the Hawaiian Luau or, more accurately, Kalua Pig. While lots of people do this in many different ways there are a few basic steps you can take to make it turn out right. You can use this cooking method for large hogs, whole lamb, a side of beef, or virtually anything else you have that just isn't going to fit anywhere else.
Digging the Pit
The size of the hole in the ground you need is determined by what you are going to cook. The pit needs to be about one foot larger in every direction. If you have a pig that is four by two feet roughly in size then you need a hole six by four feet. The hole should be about three feet deep. The size of the hole is going to determine the size of the fire and how much of everything else you are going to need, so you need the hole first.
Lining the Pit
Most pits are lined with stones or bricks. This is done to even out and hold in the heat. Large stones, about the size of your head, are perfect. One rule, though, is to avoid stones that have been in saltwater (like the ocean) in geologic time (say the past few million years). These stones have a tendency to crack, break, and sometimes downright explode. If you plan on doing this a lot lining the pit with bricks is a good idea.
Building the Fire
You are going to need a lot of hot coals to do your pit cooking. Traditionally, you would fill the pit with logs and burn them down to coals. This process can take the better part of a day. Some people choose charcoal but you are going to need a lot and since the fire isn't going to produce much smoke to flavor the meat you can go with the cheapest solution. What you are going to aim for is about a foot deep of burning hot coals before you start the actual cooking.
Wrapping the Meat
Whatever it is you choose to cook needs to first be flavored and then wrapped. Some people will say that if you are doing a large animal you should place hot rocks in the body cavity. What you do need is a secure package to put in the fire. This means tying up the meat firmly. Some people use chicken wire to wrap it together. This makes a good, tight package. In the old days, an important part of this wrapping was banana leaves (or other large leaves). This provided protection from the fire and moisture to the meat. These days' burlap bags are used to make a damp surface and aluminum foil is used to separate the meat from the coals.
The basic wrapping instructions are to take the seasoned and prepared meat. Wrap tightly in many layers of foil and then wrap that in lots of wet burlap. Finally, you want to wrap that in a heavy wire frame. This holds the whole thing together and gives you something to hold on to. Once you have it wrapped tightly you are ready for the fire. One tip, if you are doing a whole hog you need the mouth propped open to let heat through.
Loading the Pit
With the help of several strong people and possibly a few 2 x 4’s, you can now lower the meat into the pit. As soon as the meat is in the pit you need to cover it up. This keeps the burlap from burning by starving the fire of oxygen. The coals will remain hot for days, but you won't have an actual fire anymore. This can be done by covering the pit in dirt but then you'll have to dig it all out later. You can use a large sheet of metal, but what you need to do is cut off the air from getting into the pit. Otherwise, the burlap and then the meat will burn. By covering the pit you maintain a constant temperature that is perfect for cooking.
This is going to take a while. If you have a large hog with loads of vegetables, you could be looking at the better part of two days. Generally, though, the cooking time is going to be around 12 hours. The size of the pit dictated the size of the fire and therefore, the amount of heat in the pit. This controls the cooking time. If you built the right size fire you should have about the same amount of time, no matter how much meat you have in the pit. Traditionally, the meat goes in the fire at night for eating the next day. Since the meat is tightly wrapped it won't dry out and can tolerate a little overcooking so you have a large window to work with.