Generating Steam in a Wood-Fired Oven

A question of steam…

On artisan bread baking forums, you hear time and time again that one of the keys to baking great crusty bread is steam.  Another key is of course a lot of heat.  So while the wood oven gives you the heat, how do you get the steam?  And why would you want it?

Firstly, there are the caramelization and Maillard reactions, which will cause the desirable browning of the outside of your loaves.  Unless the surface sugars of the dough are in solution (dissolved), caramelization may be more like incineration. Secondly, without steam, you will get a thick and dry crust, which is less desirable than the crackly and thin crust you can achieve with steam.  Thirdly, steam around the outside of the loaves will delay the hardening of the crust allowing the loaves to expand more in their first few moments on the hearth.

In fact, this early growth process is caused by steam generated inside the dough for three reasons – but especially the heat of the hearth converting dough moisture to steam at the surface at which the dough meets the hearth (the bottom of the loaf) . However, in a (nearly) sealed unit like a wood-oven with the door plugging the entrance, if you are baking a few loaves at once the dough will release a lot of moisture which will contribute a steamy atmosphere – so once baking is underway, you are going to have self-generated steam.  So the crux of the matter is getting moisture in the right places (i) before the loaves go in, and (ii) during the first few minutes as the crust forms.

I wet the surface of my loaves liberally with a £3 garden centre hand-pumped spray gun (right hand side), and once the loaves are in the oven the professionals use a hand-pumped pressure-spray like the one on the left.  Also available from a garden centre.

So while professional bakeries might sometimes use steam injection rack ovens which cost many thousands of pounds, you can get a great result using cheap tools from the garden centre.  I have another method using a £5 pack of lava rock in a steel baking tray.

Once the fire has been removed, I put my tray of lava rock in the oven to heat up as the oven temperature evens out, carefully depositing around 200mL of hot water onto the rocks while wearing a glove, at arms length.  I load the oven with my loaves at this point.

You can see the steam rising in this example.  Remember that very hot steam is mostly an invisible gas, and that steam is dangerous and can cause burns. This is especially important if you are opening the door to a steam filled oven. Moving forward I’ll be using a pressure sprayer to wet the lava rock, removing the danger another yard from myself…

I’m currently avoiding pressure spraying the hot brick surface directly in case I cause damage to it, though that may be overkill as a 300ºC surface will probably turn it straight to steam.

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Photograph: Generating steam in a wood-fired oven using lava rock

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About jonnyr9

I'm an enthusiastic amateur "scientific" cook and baker, and former scientist, and I like to bring scientific thinking to my cooking: thinking about what might be happening at a chemical or biological level during food preparation (including its growth, and preservation), and applying exact methods of mass and volume to core recipes, before varying them. I use an accurate weighing scale (to 0.1g). I like growing my own herbs, constructing my own raised beds, and constructing my own wood-fired pizza oven. I bring a certain level of OCD to the kitchen, and therefore my baking includes sourdough, and my pizza-making includes "reference" to the protected specifications for true pizza. If I can source "the right" ingredients for a dish, I will at almost any length (within reason) - before I find an equivalent in-country supplier. Therefore - if you've never eaten Lancashire cheese bought at Bury market near Manchester - you've never eaten Lancashire cheese. I'm going to try to include links to the same products I use in my blog, so my readers don't end up using sub-standard alternatives - "experimental replication" is key to scientific cooking. I was born in the North of England, but I live in the South, though I would prefer to live on an island in the Ionian Sea.
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