What Steam Does For Bread

Reader Melody writes this about steaming loaves of bread:

Steaming honestly doesn’t seem to help that much. My baguettes still have a thick and dull crust. Am I doing something wrong? I spray more often than you do. If you can talk a bit about this that would be really helpful. I’ve been talking to our local baker but I think he’s getting a bit tired of me.

Melody, I would be delighted, for there are a lot of misconceptions about steaming bread. It’s widely thought that steam produces thin, crispy crusts on breads. That isn’t strictly true. What steam actually does is delay the formation of a thick crust by moistening the surface of the bread and keeping it supple. This allows the loaf to expand more than it otherwise would in a drier oven. The result is a higher rise and more open crumb since the crust doesn’t harden immediately and hold the expansion in. This is actually the main benefit of steam.

In an ideal situation, once the bread has finished “springing” — about a third of the way through the bake — you quit the steaming and allow the surface of the loaf to dry out. If all goes well, what would have otherwise been a thick and crunchy crust is now a thin and crispy crust.

A further benefit of the steam is that it causes flour granules on the surface of the loaf to absorb moisture, swell and “gelatinize” (read: dissolve into their component starch molecules). Those individual carbohydrate molecules will further break down in the heat of the oven into their component sugars, which them caramelize and turn the crust brown.

So that in a nutshell is what steam does. I should add that trouble starts when you introduce too much steam and/or keep it up for too long. In that case the cool, gelatinized layer gets too thick and the finished crust becomes extremely hard and thick. The prolonged cooling also retards caramelization and keeps the crust from browning.

So that’s probably what’s happening in your oven Melody: too much spritzing! The best of all possible worlds for bread making is a moderately moist oven for the first 20-30% of the bake, then an almost totally dry oven for the rest. Make sense? Thanks for the question!

14 thoughts on “What Steam Does For Bread”

  1. It’s amazing what a difference steam makes! When I worked in a restaurant kitchen with a fancy steam-injecting oven, we turned out these gorgeous crusty brown rolls. Occasionally someone forgot to set the steam, though, and you could really see the difference: the crusts were pale, thick, and just not as beautiful. Thanks for explaining more about why!

  2. It’s very hard to get a steamy environment in your whole oven without steam injection, IMO. What you can do instead is create a bag-type lid out of foil over your bread, or I use a large loaf tin over baguettes, or a large ceramic bowl over free-form boule. Preheat the oven and the cover you’re using, then remove the cover, spray with a water bottle to create a moist environment and put it straight over the dough, then straight into the oven. After the required period of steaming, just remove the cover and continue to bake as normal.


  3. I’ve got a tip for Molly that pretty much does away with the need to steam baguettes.

    By now probably everyone is pretty familiar with the “magic bowl” technique, which is pretty much just to cover the (usually a round boule) loaf of bread with a stainless steel bowl for the first 15 or so minutes of baking. What this does it traps the steam that the dough releases and acts as a sort of steam chamber.

    Now obviously that doesn’t work for baguettes, but if you get a couple of long loaf pans for cheap and use them to cover the baguettes — it works great!

    1. I use fish poachers (ebay!) without the steamer insert to bake my long Italian/French breads. I proof them on floured towels in baskets and then use the towel as a sling to slide the bread into the hot pan. I score the bread, spritz with water, and cover. I bake them in a 450F oven or hotter. I take off the lid for the last five minutes of bake time to ensure a little more browning.
      I also make 12 oz. baguettes and bake two side by side in the poacher. They might need to be gently separated after baking but you get a nice baguette all the same.

  4. I just put a pan of water on the floor of the oven. Opening the door often just lowers the temp too much.
    I also do use a stone— preheat time increases to allow the stone to be hot enough.

  5. I use a roasting pan full of lava rocks, it’s preheated along with my unglazed quarry tiles which I use as my baking stones. I toss in 1/2 cup of hot water onto the lava rocks a few seconds before I put in my bread. I do it again two minutes later and then I let the bread bake. I haven’t sprayed the surface of bread in years, I never liked what it did to the crust. The lava rock method was recommended by Cooks Illustrated.

    1. Lava rocks indeed! Never heard of that but I can see where the porous texture would let steam out steadily. Very clever!


      – Joe

  6. Joe,

    I was skiing in VT this weekend (which, BTW, was one of the most fortunate decisions I’ve made this year, as the conditions were ideal!) and the house we were renting happened to have a sauna. Now, not having one, or a membership to a gym with a sauna at home, I was smitten and immediately turned the thing on to warm up. After an hour or so of preheating, I stepped in and was surprised at how lackluster the sauna felt. I then proceeded to dump about half of the bottle of water I’d brought with me onto the cinders, and experienced a dramatic uptick in temperature, with my body immediately reacting to the increased perception of heat.

    All of the above is an interesting anecdote which, while true, brings me to my question for you: Are you sure that the addition of steam is in fact lowering the effective temperature of the oven, and not serving as a method for transferring heat more effectively? I would think that the higher effective temperature, in conjunction with the gelatinization of the outer layer of starch would serve to enable a higher oven spring as well. What are your thoughts?

    Chris R

    1. Yes you are completely right, Chris. I fell back into an old habit when I used that “cooling” term. The idea of “cooling” steam is a popular myth among bakers that still persists. A physicist reader broke me of that habit (though clearly only partially) a few years a ago. I can still remember his comment: “When’s the last time you stuck your face into steam to cool it?” Thanks for reminding me of my error!

      The moisture does keep the crust supple, that much is true, and you’re completely correct in that steam would in fact create a higher temperature on the surface of the bread. And that helps with both spring and caramelization.

      Thanks for coming to my rescue!

      – Joe

  7. thank you so much! i think i could have used a bit more steam earlier on and then ill take off the cover i had over the vent after that.

  8. oh and i’m about to try covering the bread. i’m going to use a glass pyrex bowl and after i accidentally left it in the oven when my parents were preheating for dinner, i now have practice at removing it while it’s hot. i’ll have to do a boule shape but it’s the best i’ve got.

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