Steam, smoke and damp patches in the first fires

Your new oven is smoking, and the inside has gone black in patches. Here are some causes to look at, and your own manual comes first.

Cause 1: oil from the making of the oven

One maker says it is normal to see some black smoke at first use, and that it's the cooking oil used in the de-moulding process. The smoke will be a little heavy for the first 2 days and will dissipate through the rest of the curing process¹.

That heavy smoke early on is that maker's normal case for its own oven¹. Check your own manual for what's normal for yours. Another maker's oven may not be made the same way. If your manual doesn't mention smoke, ask.

The same maker offers a tip for the low, smoky early fires. Leaving the door partly open will help direct the smoke up the vent, because the smoke is heavier while temperatures are low¹. Check your manual for how far to open yours.

Cause 2: soot from small, cool fires

A new oven can look dirty after the first fires. One guide describes how the black clears as the oven gets hotter. In the end the soot burns off, the moisture is pushed out and the dome looks clean².

So dark soot early on isn't necessarily a fault. It may simply be the soot that later fires will burn off.

Cause 3: parts of the oven are still damp

Dark or sooty patches that linger can mean part of the oven hasn't dried yet. The same guide describes a re-cure. Part of the dome had turned white, yet a significant strip of black remained along the walls of the vault². That meant the job wasn't done. The vault is the curved inner roof and sides.

That example is a guide's own account of one oven, not a rule. But it fits the idea that moisture leaves from different spots at different speeds. You can also check by touch once the oven has cooled. Does it feel cool and damp when you reach in?² If so, it may need more gentle heat, in line with your manual.

What about steam?

None of the sources I've saved describe steam coming out of a new oven in detail. They say moisture is pushed out as the oven heats². One clay oven maker says a progressive heating is how any humidity disappears before use³.

If you see vapour, treat it as a sign of water leaving, and keep to the maker's schedule. Don't turn up the heat to hurry it along. Hot fires too early risk cracks. See hairline cracks.

Skip shortcuts like a space heater, which that same maker rules out for curing¹.

Cause 4: the wrong fuel or wet wood

Heavy, smelly smoke can also come from what you're burning. One maker allows solid wood fuel only, and its do-not-use list includes charcoal, pressure-treated lumber, chipped wood products, sappy wood such as pine, and laminated wood¹. Another guide points readers to properly seasoned wood so that no extra moisture goes into the oven². Seasoned wood is wood that's been dried for a good while.

When to stop

I haven't saved a source with stop signs for smoke, so follow your own manual for when to stop a fire and how to put it out. If something looks wrong or your manual doesn't cover it, contact the maker with your model name and what you saw. Always cure outdoors, in the open air. The outdoor safety page explains why. When the dome finally turns pale, see how to know curing is finished.