Sac or oven

The difference is not that one is old-fashioned and the other convenient. Under a sac the heat comes from above, from embers heaped over the dome, and falls as they burn down; moisture from the food stays trapped under the lid and returns to it. In an oven the heat comes from elements, holds at the number you set, and carries the moisture away. Everything else follows from those two sentences.

Where the heat comes from

A sac is not put on the fire — the fire is put on it. Embers are raked with a paddle over the dome and around the rim, so the vessel heats the food from above, radiating from the inner face of the dome. From below the crepulja heats it, standing on the hot hearth and conducting through its base. The food is closed between two hot clay surfaces and never needs turning.

An oven works otherwise: elements heat the air, and the air heats the food. Air has little thermal mass, so every opening of the door drops the temperature and it returns only after some minutes. Clay has a great deal of it — a heated sac goes on radiating after the embers have halved, and that inertia is what keeps the baking even.

Moisture: a closed dome against ventilation

This is the difference that shows most. Under the sac the steam has nowhere to go: it rises from the food, gathers on the cooler inner face of the dome and falls back as drops. The meat bastes itself, and potatoes beside it steam in their own vapour before they begin to roast. The unglazed clay also takes up and gives back some moisture, so the inside turns neither dry nor swimming.

An oven is the opposite: it has a vent and must have one, or it would become a steamer. A fan, where there is one, dries faster still. Which is why in an oven things are covered with foil or given a splash of water — both of them attempts to produce by hand what happens under a sac by itself.

A falling temperature against a steady one

An oven holds the number. Set 200 °C and you have 200 °C to the end, which is priceless whenever a recipe depends on accuracy — a cake, a dough that rises, a fish that dries out in minutes.

Under a sac there is no number to set. There are embers that give their most at the start and less every hour after, unless they are renewed. For a large piece of meat that is the better curve: a fierce beginning closes the surface, and a long gentle phase breaks down the connective tissue. For anything that needs precision, the same curve is the problem.

Smoke

Embers of hardwood give aromatic compounds that enter the food. No oven setting reproduces that — it is a matter of combustion, not temperature. If that smell is the reason you bake under a sac at all, an oven is not a substitute but a different technique.

What is worth baking under a sac, and what in an oven

• Under a sac: large cuts of meat, lamb and veal with potatoes, bread and pogaca, dishes that run for hours
• Under a sac: anything where the smoke and the moist enclosure are the whole point
• In an oven: cakes, risen doughs, anything with an exact temperature and an exact time
• In an oven: small meals and anything that has to be ready within half an hour
• In an oven: when there is no hearth, no wood and no hour to spare

Can a sac go in an oven

It can — the crepulja with the food and the sac over it will fit a wider oven, and there they work as a covered clay baker. You get the trapped moisture and the gentle radiance of the clay, so one of the two main differences. You get neither the smoke nor the falling curve of the heat. It is an honest compromise for a flat without a hearth, but it is not the same dish and there is no reason to pretend it is.

Heat source

sac: embers above, crepulja below · oven: elements through air

Temperature

sac: falls as the embers burn down · oven: steady, as set

Moisture

sac: stays under the dome and returns · oven: leaves by the vent

Smoke aroma

sac: yes, from hardwood · oven: none at all

Setting up

sac: wood and embers, usually about an hour · oven: a few minutes

Best for

sac: large cuts, bread, long bakes · oven: precise baking