There are basically three types of fire used in barbecuing or smoking food. There is the "hot" fire, the "moderate" fire, and the "cold" fire. Grilled steaks and salmon are best when cooked over a hot fire with moderate smoke. Roasts, turkey, chicken, and ribs are best cooked over a moderate fire with lots of smoke. Smoked fish and jerky are best prepared with a warm or cool smoke.
The hot fire, as referred, is essentially a bed of hot coals with little or no flame. If you are using wood for fuel, then burn the wood until the surface of it is covered with ash. This may require turning the pieces of wood once or twice. Then spread the pieces of wood enough to diminish the flames. This type of fire is used for food types which cook quickly. Hamburgers, shish kabob and steaks fall into this category.
The moderate fire is produced from a hot fire by sprinkling with some wood chips which have been soaked in water for 30 minutes, and then covering the fire for a short period of time. Select a hard, long lasting wood for the moderate fire. The moderate fire is used for foods which take longer than 30 minutes to cook. Turkey, roasts, chicken, rack of lamb, and large pieces of fish would be cooked with a moderate fire. Cooking with the moderate fire usually requires a lid over the barbecue.
The cold fire is a source of warm or cold smoke to the food being processed. The warm smoke condition can be achieved simply by pushing the coals off to one side of the barbecue, placing the food on the opposite side of the grille, adding the wood chips, and then covering. The control of ventilation will cause the smoke to circulate around the food inside, thus imparting that unique barbecue flavor.
The true cold smoke is a little more difficult to achieve. The larger smokehouses, in which hams and bacon are prepared, use this technique. From a warm smoke condition, the smoke must be "piped" to a contained volume in which the food is housed. The fire is in a separate housing from the food, so the food receives no heat. It is therefore not "cooked", but rather flavored, and perhaps somewhat preserved, depending on how long the food is in the cold smoke.
About the Fuel
The secret to a good flavor in barbecued foods lies largely in the smoke (and flavor) from the fuel used to make the fire. The charcoal briquettes bought in the market are useful for steaks, spareribs, and most other foods, but will not impart that special flavor which is so unique to a truly delicious barbecue. Avoid using a charcoal starter fluid for the fire, since it tends to impart an adverse taste to the food. A few pieces of cardboard will work just as well. The fuel which I prefer for grilling food is oak wood. Oak imparts a subtle flavor to the food which is very pleasant to the palate and is not overpowering.
The smoke from the fuel in a barbecue is what really imparts the flavor to the food. Achieving the proper smoke is like using herbs in a sauce - a little of this and a little of that will make for a good flavor. A dash of hickory, a sprinkle of alder, a corncob, and voila! There are more variations to the smoke than there are types of wood.
The best woods for a barbecue are the hardwoods. Oak is usually preferred because of its gentle flavor. Mesquite has become a favorite in recent years because it burns hotter and longer than most other woods and also has a subtle flavor. Mesquite charcoal has become more available in markets for a good combination of convenience and quality of smoke. Hickory chips are a good addition to a fire for flavor providing that they are used in moderation. Too much hickory will impart a bitter taste to the food unless it is used over an open fire for barbecuing rather than for smoking. Below is a list of woods which I commonly use for making smoke in my barbecue, and a few words about how to use them.
There are many woods to avoid as fuel for a barbecue. Among these are all of the resinous and soft woods such as pine, peach, apricot, redwood and eucalyptus. In general, any wood which has sap seeping from the bark is to be avoided. Also, any strong smelling wood such as cedar or eucalyptus should not be used.