Most dishes bake on the middle rack, where heat from above and below is most balanced. Pastries that should crisp on the bottom go on the lower rack; dishes that should brown on top bake near the upper rack. Because rack position changes its distance from the heating elements, it is the easiest way to change the result without changing the temperature.
Heat inside the oven comes from 3 sources: the lower heating element, the upper heating element, and the air heated by both. The rack determines which of these sources the food is closer to. A baking sheet on the lower rack receives stronger heat from below; a baking sheet on the upper rack is exposed to radiant heat from the upper element. The middle rack sits between the 2 and gives the most balanced result. In a convection oven, circulating air reduces the difference between racks, but does not eliminate it. So unless a recipe says otherwise, place the baking sheet on the middle rack.
The lower rack is for foods that need more cooking on the bottom. Pide, lahmacun, pizza, börek (Turkish savory pastry) with a soggy bottom, and pies are baked on the lower rack; if desired, use a preheated baking sheet or pizza stone. Bread also does well on the lower rack during the first stage of baking. The risk is that the bottom may burn if the baking sheet is too close to the lower heating element. In that case, put a second, empty baking sheet underneath to soften the heat, or move the rack up one level.
The upper rack is for dishes that should brown on top. Finish gratins, cheese-topped baked pasta, and vegetables to be charred on the upper rack. If using the broiler, keep the food 10–15 cm from the upper heating element. The opposite risk on the upper rack is that the top may darken before the inside is cooked. So bake thick dishes on the middle rack and move them to the upper rack only for the last few minutes. Do not bake cakes or cookies on the upper rack, because their tops set too early. Do not leave a baking sheet unattended in the oven while broiling; it can brown in 1–2 minutes.
The baking sheet’s position on the rack also matters. Keep it from touching the oven’s back or side walls, leaving enough space for air to pass along every edge; in a convection oven, do not block the fan. If baking 2 sheets at the same time, leave at least 2–3 cm between them, arrange them diagonally rather than directly above one another, and switch their positions halfway through baking. The convection setting gives more consistent results than the conventional setting when baking 2 sheets.
Changing the rack can take the place of changing the temperature. If a dish is browning too quickly on top, moving the rack down one level is often enough instead of lowering the temperature; if the bottom is cooking too slowly, lower the rack. Adjust rack guides while the oven is cool; do not move a rack in a hot oven. A baking sheet can slide forward if the rack is not seated fully. Decide which rack to use before putting the baking sheet in the oven; opening the door to change rack positions loses heat and creates a burn risk. Put the rack in place while the oven preheats.