Charcoal is ready after the flames have gone out and its surface is covered with a thin layer of gray ash; this generally takes 20–30 minutes from the time it is lit. Do not put meat on the grill while flames are still present: flames do not cook the meat but coat its surface with soot and leave a bitter taste. Ready coals glow red in the dark and look ashy and dull in daylight. You can also test the heat by hand.
Freshly lit charcoal is still burning off its volatile compounds, a process that produces flames, smoke, and soot. Smoke flavor on the meat during this stage is not the desired grilled flavor; it is a burned, bitter taste. Once the charcoal has burned off these compounds, the flames go out and stable, heat-producing coals remain. The same waiting period also lets the heat even out: some pieces in a newly lit pile may be glowing while others are still cold, so meat will not cook evenly on the grill.
You can tell the coals are ready by looking at them. Their surfaces should be covered with a thin layer of gray ash, the flames should be completely out, and the pile should have settled slightly. In daylight, the coals look dull and ashy; in the dark, a red glow can be seen beneath the ash. Charcoal that is still shiny black on the surface or has flames coming from its edges is not ready. The wait is usually 20–30 minutes from lighting, but it varies with the type and size of the charcoal pieces. Hardwood charcoal such as oak takes longer to catch but burns longer; lighter charcoal is ready sooner and burns out sooner.
You can also test the heat by hand; this is the only reliable measure when you do not have a thermometer. Hold your hand one hand span above the coals and count how long you can tolerate the heat. If you can hold it there for 2–3 seconds, the heat is high; use that area for thin steaks, meatballs, and chicken wings. If you can hold it there for 5–6 seconds, the heat is medium and suitable for thicker cuts. If you can hold it there for 8–10 seconds, the heat is low; use that area to keep cooked meat warm or slowly cook thick cuts. This test also works on a gas grill because the actual heat above the grate matters, not the indicator.
The lighting method also affects the result. A charcoal chimney starter gives the cleanest result: put the charcoal in the chimney, place newspaper or a fire starter cube underneath, and let the charcoal catch and burn upward on its own; the top pieces develop ash in about 20 minutes. If you use lighter fluid, wait until its smell has completely dissipated; otherwise, its odor will transfer to the meat. Use nothing as a fire starter except paper, cardboard, or a fire starter cube.
Once the charcoal is ready, spread out the pile and arrange the coals; they do not all need to be spread evenly. Leave a thick layer on one side and a thin layer or no coals on the other, so cuts of different thicknesses can cook in different zones. Place the grate at this point and let it heat up. Coals eventually burn out, so for a long cook, light new charcoal in a separate area and let it develop ash before adding it; do not put unlit charcoal directly on the grill. After the added charcoal lights, the heat rises for a while, so do not place meat over it immediately.