A baking steel or stone is thermal mass, and that is the whole benefit

Everything here earned its place by changing an outcome. Nothing about baking stones and steels is included to round the number up.

What thermal mass does

A hot slab of stone or steel holds a large quantity of energy and releases it into anything placed in contact with it. Air at 250C carries very little energy, so a dough sitting on a tray heats mainly by radiation and slow convection. The same dough on a preheated steel receives energy by conduction, which is dramatically faster.

That is why a pizza base cooks in three minutes on a steel and takes ten on a cold tray. The slab also stabilises the whole oven by damping the thermostat swing and refilling heat after the door opens.

Steel versus stone

Steel conducts heat several times faster than cordierite or ceramic of comparable thickness. For pizza that is usually an advantage, giving faster base browning and a better rise from the initial burst.

In the tin, stone releases heat more gently, which some bakers prefer for bread where a very fast base can scorch. Steel is heavier for a given size, more expensive, and effectively indestructible. Stone is cheaper and lighter but can crack from thermal shock, particularly if water is spilled on it hot.

Preheating it properly

A slab needs far longer than the oven air to reach temperature, typically forty five minutes to an hour at full heat. Fifteen minutes gives you a warm slab and none of the benefit, which is the most common way people are disappointed. An infrared thermometer is the easy way to check the surface, though time is a reasonable proxy once you know your oven.

Leave it in place permanently on a lower shelf if you can, since it improves every bake even when unused. The cost is a longer preheat for everything, which is a real trade in a busy kitchen.

What to use it for

Pizza is the obvious case, where the base needs to set and brown before the toppings overcook. Free-standing bread benefits substantially, since the base receives the heat it otherwise struggles to get.

Tarts and quiches placed directly on a preheated slab are far less likely to have a soggy bottom. Biscuits and small items gain little, since they are thin and the air alone cooks them fine. Cakes generally do not want a fast, hot base and are better on a normal shelf.

Size and placement

The slab should leave a gap of at least a few centimetres around the edges so air can circulate. Blocking the whole oven width traps heat below and creates a very uneven cavity. Placing it a shelf below the food, rather than directly under it, still improves stability without over-browning bases.

For pizza, high in the oven is usually better, so the top browns at the same rate as the base. For bread in a pot, the slab does little, since the pot is already controlling the heat transfer.

Care and longevity

Never pour water onto a hot stone, since thermal shock is the main thing that cracks them. Do not wash stone with soap, because it is porous and will absorb it; scrape and heat clean instead. Steel will develop a dark seasoned patina from baked-on oil, which is cosmetic and harmless.

Oil a steel very lightly after cleaning if your kitchen is humid, since bare carbon steel rusts. Both will outlast the oven they are sitting in with minimal attention.

Everything above, in order of what to do first

1. What thermal mass does. A hot slab of stone or steel holds a large quantity of energy and releases it into anything placed in contact with it.
2. Steel versus stone. Steel conducts heat several times faster than cordierite or ceramic of comparable thickness.
3. Preheating it properly. A slab needs far longer than the oven air to reach temperature, typically forty five minutes to an hour at full heat.
4. What to use it for. Pizza is the obvious case, where the base needs to set and brown before the toppings overcook.
5. Size and placement. The slab should leave a gap of at least a few centimetres around the edges so air can circulate.
6. Care and longevity. Never pour water onto a hot stone, since thermal shock is the main thing that cracks them.

The takeaway

Preheat it properly or leave it out, because a lukewarm slab is worse than no slab at all.

Patience is an ingredient, and it is the one people leave out.