How to build the right kind of fire
The right kind of fire for aluminum foil cooking is really no fire at all, but rather a bed of hot coals. The Boy Scout Merit Badge Book on cooking explains how to get a bed of coals as follows:
“The camp fire generally supplies a good bed of coals, but sometimes this is needed in a hurry, soon after camp is pitched. To get it, take sound hardwood, either green or dead, and split it into sticks of uniform thickness (say 1¼ inch face). Lay down two bed-sticks, cross these near the ends with two others, and so on up until you have a pen or crib a foot high. Start a fire in this pen.
“Then cover the top of the pen with a layer of parallel sticks laid an inch apart. Cross this with a similar layer at right angles, and so upward for another foot. The free draft will make a roaring fire, and it will all burn down to coals together. The thick bark of hemlock, and of hardwoods generally will soon give you coals for cooking. To keep coals for a long time cover them with ashes, or with bark which will quickly burn to ashes.”