A baking stone is a flat cooking surface used in baking. They may be made of ceramic, stone, or more recently, salt. Food is put on the baking stone, which is then placed in the oven, though sometimes the stone is heated first. Baking stones are used much like cookie sheets, but may absorb additional moisture for crispier food. Due to the thermal mass of baking stones and the material's property as a poor heat conductor, food is less likely to burn when using a baking stone than when using metal or glass bakeware. Baking stones are a variation on hot stone cooking which is one of the oldest cooking techniques known. Baking "stones" may be purchased as unglazed ceramic tiles, unglazed fired clay tiles and quarried tiles, very cheaply from tile shops and hardware stores.
To prevent fracturing of the stone by thermal shock, some bakers place the baking stone in a cold oven and heat it over at least 45 minutes, then allow it to cool down slowly inside the oven after switching it off. Because of the possibility of rapid temperature change, baking stones should not be left in an oven while it is in self cleaning mode. Some cooks recommend sprinkling corn meal, semolina, bread crumbs or rice flour on the baking stone to prevent the crust from sticking. Because it is porous, a baking stone will absorb any fluid which it comes into contact with, including detergent. They should be cleaned with a dry brush and then plain water.
When designed for cooking pizzas, a baking stone is often referred to as a pizza stone. Using a pizza stone more or less mimicks the effects of cooking a pizza in a masonry oven. The porous nature of the stone used also helps absorb moisture, resulting in a crispy crust. Small pizza stones can be purchased to fit in any conventional cooking oven or an enclosed barbecue-style grill. High-end ovens sometimes offer optional pizza stones that are specifically designed for each oven model and may include a specialized heating element.