April 4, 2024 - 6:52pm
Something that puzzles me
Hello bakers,
I recently read Sarah Black’s One Dough Ten Breads book and while I found it very interesting, there was something that puzzles me in her baking instructions : for all the recipes she uses the lava rocks method to create steam in the home oven, but she never removes them after the customary first 15-20 mins which is what I’ve learned ever since I started making sourdough and other artisan loaves.
As far as I understand it, the steam is only useful/required during the initial baking time to encourage the oven spring correct?
BTW it’s a shame that her book is out of print, I think is a book worth having on hand.
thanks, look forward to your comments.
Share
Steaming in a home oven does not work as it does in professional ovens. I don't think it works the way most people think, either.
In a home oven, when you pour water over the rocks, it generates a burst of steam - no surprise. Most of that steam leaks out of the oven quickly - the oven isn't hermetically sealed and it isn't a pressure cooker. Steam at room
temperaturepressure (at sea level) is going to be at 212 deg F/100C since it can only be hotter at a higher pressure. So very quickly the steam pan will cool down to that temperature. If you pour more water in at this point, you won't see another burst of steam.The steam will condense on the cooler surface of the loaf, causing it to gelatinize and stay soft until the surface heats up enough to set. In my oven, this process is much more effective than spraying the loaf before putting it into the oven.
Whatever water is left in the steam pan will humidify the air in the oven but won't generate steam, at least not much. The oven will be heating up again, but the steam pan, being covered by the baking stone, may or may not heat effectively depending on the details of the oven. In my oven, the steam pan region doesn't get much over 300 deg F or so, even though above the baking stone, where the bread is, it does recover to a much higher temperature.
By the time you are thinking of taking out the steam pan, it won't matter much. Most of the water remaining in the pan will have evaporated. The air in the oven might be able to dry out a little more, but my crusts come out well-cooked even though I leave the pan in there.
If you use the trick of putting rolls of wet towels into the steam pan, then taking them out might let the oven air dry out more - maybe. I haven't tried that method.
In my oven, most of the expansion of the loaf takes place within the first five minutes. After that the crust has set enough that there's little more rise. I know some people's ovens work differently and seem to be able to prolong the rising period. But don't count on it. I've baked bread in several home ovens and they all performed about the same.
I have actually turned the oven off after generating the steam (well, I turn the setting down to 300 deg F/150C, not literally off). The bread rises at least as well and probably better than if I leave the setting at the full baking temperature. This shows that the steam generation and remaining moisture dominate the oven temperature for some time into the bake. The baking stone with its large heat capacity keeps feeding heat into the base of the bread, causing it to heat up and rise even as the oven air is cooler.
TomP
Very good explanation, Tom.
Dave
Thanks : ) I have corrected one word (from "room temperature" to "room pressure").
It's true that liquid water at sea level vaporizes at 212F, but I don't understand the claim that steam can't exist at higher temperatures at that pressure. What I would understand is a claim that it can't exist at lower temperatures at that pressure. I guess your main point is that the humidity of the oven loses relevance to oven spring once the loaf has baked for a while. That would be fun to test because it would be nice not to have to bother pulling a hot steam tray out an oven or try to calibrate the amount of water to add so that it's exhausted partway through. It would be even more fun to hear that somebody else has already tested it.
When you increase the temperature of steam above 100°C, one of two things must happen:
In addition, as long as there is any liquid water, either in the steaming pan or in the bread/dough, heat will preferentially contribute to the latent heat of vaporization of that water, rather than creating a greater difference in temperature between the steam and the rest of the contents of the oven.
I personally never remove my pan of rocks from my oven. I just open the door and unplug the vent when I don't need the steam anymore. Even if there was any water left in the pan, any further water vapor created wouldn't be enough to make a difference before blowing out the vent.
However, if you use the wet towel method, it is important to remove them before they dry out or else you'll burn them.
Steam can exist at higher temperatures but only if the pressure is higher. There is a direct relationship between the temperature of steam formation and the pressure. That's what a pressure cooker does for you - it lets you cook at a higher temperature without the formation of steam. When you pour water on the rocks, copious amounts of steam are generated at a higher temperature (the temperature of the rocks, which start to cool down) , and the steam pressure is higher than atmospheric as a result. But your oven cannot contain the higher pressure and that's why the steam is forced out of the oven. If you were to open the oven door (keeping your hands protected and your face well out of the way - don't really do this, I've already done it for you!) you would see a large amount of visible vapor puff out of the door.
When the steam touches the cool loaf, it condenses and gives up its latent heat. If you could see it you might even notice water appear on the surface apparently out of nowhere and run down the side of the loaf. The latent heat causes the surface to heat up much faster than just humid oven air would be able to do.
Sometimes the temperature and moisture might get high enough to cause some gelatinization just at the surface. I think that this is the reason why free-standing loaves sometimes get a shiny surface but a dutch-oven-baked loaf generally does not.
Steam can exist at a higher temperature than 100 °C; it is superheated steam. It is generated by passing saturated steam through a chamber (superheater) heated at a higher temperature. Unlike saturated steam, superheated steam is not as efficient in cooking because its heat transfer is similar to air. However, superheated steam can perform more "work" in the thermodynamic sense because of its high energy content. This energy is especially useful in applications like turbines and railroad steam locomotives, and in these applications, the superheated steam is at elevated pressure. One application for superheated steam at atmospheric pressure is drying; it is more efficient than hot air alone:
Drying with superheated steam at atmospheric pressure
It's unlikely that the steam in the oven becomes superheated, despite the higher temperature of the oven surfaces. Until all the water evaporates, there will be an equilibrium with water in the oven (as stated above). Add in the fact that ovens are not sealed devices like piping and allow the steam to escape.
You are correct that "steam" does not exist below 100 °C; is is just water vapor. But the amount of water vapor does increase with temperature and would increase the humidity in the oven.
I won't dispute that. In fact, I'm sure that the steam generated by pouring water onto preheated rocks comes off the rocks above the boiling point. In the process the rocks will get cooled down to the boiling point (if there is enough water). It will condense on cooler surfaces like the bread, and leak out through any unsealed joint or opening until the pressure returns to atmospheric. At that point the interior of the oven will no doubt be more humid than it otherwise would have been, but there is no longer an excess of pressure to drive the humid air forcefully out of the oven. If you doubt this, compare generating the burst of steam and then opening the oven, to receive a burst of steam in your face - careful, don't get burned! - with opening the oven after five minutes and not seeing or feeling much if any visible vapor. [Please don't really stick your face in front of a steaming oven!]
In a strict sense, the water vapor in the air inside the oven can be considered steam at the local air temperature in the oven. But it's not condensing and giving up its latent heat to the bread to any degree any more. In fact, the steam burst will also have cooled down the air in the oven, which will take some time to recover.
There won't be much if any more steam condensing and giving up its latent heat into the bread - the surface of the bread will be too warm by then and the moist air too cool. The remaining water in the steam pan will not be boiling off as a visible cloud of steam (at least in my oven - maybe some others can reheat the steam pan more than mine) The humidity will come down over time as it tries to get into equilibrium with the air outside the oven.
It's interesting to read in the linked page that one advantage of the superheated steam approach for drying is that the steam excludes oxygen from the material being dried.
Cool beans. Please forgive my beating this dead horse (and horse lovers for my insensitive metaphor), which isn't as close to bread baking as some other topics.
My picture of things is that the air in an oven will consist of a mix of gases, all of which (by definition) have a boiling point below the temperature of that air. Water is one of them, and we call it steam when it's gaseous. If there is a water pan in an oven, there is a process of the liquid water becoming gaseous - creating steam - and that's going to consume a fair amount of - but not all - of the themal energy being delivered to the oven contents. We've set the oven to a certain temperature, and we expect the air in the oven to be at that temperature, though of course there is local variation. In particular, air near that water pan, and near the bread, is going to be cooler, and near oven walls, hotter. Let's agree that it's not steam after it mixes with the other gases. With that qualification, I agree - at long last! - that the steam in the oven is never above the boiling point of water at atmospheric pressure.
I have no idea how to measure the humidity in an oven, but what we want is high humidity in the early stages of a bake because we like what it does to the crust of the bread - specifically, it keeps the crust elastic longer.
The learning for me in this thread is the idea that the humidity of the air in the oven loses its effect as the loaf bakes, and that therefore there is no need to remove a steam tray or lava rocks, or, equivalently, calibrate the quantity of water to add so that it's exhausted mid-bake.
Like many home bakers, I do a lot of bakes in pairs of Dutch ovens. It occurs to me that a simple way to test that hypothesis is to simply leave one lid on next time I do a bake, and compare the loaves under the assumption that the key difference will be in the humidity the loaf experiences in the second portion of the bake. Seem logical, or do I make too many assumptions?
It's worth doing. One difference from baking a free-standing loaf is that the condensing steam won't settle over the loaf in the DO as much, since its surface is partly shielded by the high sides. I just this morning baked an 80% whole wheat loaf in a loaf pan, but with the baking steel and initial steam. After about 5 minutes I peeked in and there was a glossy sheen over the top surface of the loaf. Some of it was still left after baking. So I expect you to see something.
It's also interesting that you can bake a loaf in a DO without preheating it. I have read someone who said that you get more rise when the loaf is preheated. I have not tried both ways side by side with the same dough, one preheated pot and the other not. So I don't know from personal experience how much difference the preheating makes. But you can definitely bake a respectable loaf without preheating.
Four years ago, the FoodGeek channel on YouTube did an experiment baking in DOs with four conditions, and his learning was that the best oven spring was obtained with the orthodox approach - that is, the oven was preheated with the DOs inside. You can see that experiment here, with the results presented at 9:40:
https://www.youtube.com/watch?v=8CyYA-p1dMA
That channel has been the source of some decent learnings for me over the years. For example, he doesn't find any advantage is doing an autolyze (I do them anyway).
Interesting.
For an autolyse, I usually give the dough a rest after quickly and roughly mixing the ingredients. I don't know that it matters for the final result, but it makes the initial kneading or stretching (after the rest) much easier and faster.
Also, leaving out the salt until after the rest (which is usually thought of as being a feature of the autolyse) makes the dough initially slacker (more extensible), which can be helpful if you know that your dough is going to be very tight. Conversely, if you expect the dough to be very slack, as with "ancient grains" (emmer, einkorn, etc) or high-hydration doughs, mixing in the salt right at the start will help to counteract the slackness.
I just watched the episode. The hydration was pretty high, so the loaves would tend to spread out sideways as they soften. The cold/cold condition would have been affected by this the most. The crumb of each cold DO loaves looked well open. I would be inclined to look for a DO that was smaller so that it would prevent the dough from spreading out much sideways, for baking in a cold DO condition.
For a free-standing loaf on a baking stone or steel, the hot stone pumps a lot of heat into the loaf while the steam keeps the surface relatively flexible and generates more of an upwards expansion. Of course, this works best for loaves that don't tend to slump and spread sideways, so ultra-high hydration loaves will come out flatter (e.g., glass bread) or want to be baked in a loaf pan.
Hi Tom,
As always excellent and clear explanation, thank you!
I just want to say thanks to all of you for taking the time to explain things so thoroughly. I've learnt a lot from reading your comments.
Here's the procedure that works best for me in a home electric oven; the oven has a convection oven (great for roasting chicken) but I don't use it for baking. I have tried lots of variations, but this one works better than a Dutch oven (for me) and lets me bake 2 loaves at once (on the lower stone). I'm pretty sure the oven is vented so the 2nd spritz 5 minutes in really seems to help.
Oven Set-Up Photo - from the bottom up:
Bread Photos with Scoring These more or less alternate between Hamelman''s 100% Whole Wheat Workday Bread and various loaves from "The Rye Baker"; there are links to each formula in the photo descriptions.
I used to boil my water in the microwave. Then I tried using the water right out of the tap. I couldn't tell any difference in the bread. Then I realized that either way, the oven or at least the lower region around the steam tray would always end up at the temperature of boiling water - as shown by the liquid water remaining in the pan - and that's why the water temperature doesn't matter.
I tried that once and nearly got badly burned by the steaming mist that blew out of the oven door. If you must try it, I'd suggest pulling the rack with the loaf out of the oven door and spritzing it there, outside the oven. And wear a big oven mitt!
I don't think it's harmful to leave the pan in the oven. By the end of the bake it's not going to be adding much if any moisture to the oven, and there's no need to risk handling a hot unwieldy apparatus. My loaves end up with a lovely well dried-out crust anyway.
I've been turning down the oven temperature setting right before or after inserting the bread. I leave it down for 7 - 12 minutes (the actual time doesn't seem to make any difference). The bread bakes just as well and perhaps better than my old way of boosting the setting to part of the bake. Now I realize that generating the steam with a steam pan lowers the oven temperature so much that the first part of the bake is going to be at a lower temperature no matter where you put the temperature setting.
This applies when there is a well-preheated stone or (better) baking steel in place, since the preheated stone will keep pumping heat into the loaf while the cooler oven air won't set the crust as soon as a hotter oven would.
I haven't read him but I gather that much of his book relates to professional bakeries, which have very different ovens
That's very interesting. After my one nearly disasterous try I haven't tried again. Perhaps I should. I do know that adding more water to the steam tray does nothing because it's already got some remaining liquid water at this time. When you wrote "a bigger effect", what did you mean? When you spritz, I picture you spraying above the bread rather than by the steam pan. Is that right?
Here is a photo of me taking a photo of my spritz bottle. Water only spritz bottle photo
I open the oven and from just outside it I can safely spritz the loaves on the lower stone. I aim at the loaves on the stone, and get as much of them as I can without moving them (just for ease and safety), especially on top. It's possible that the spritz that lands on the sides also darkens the crust, but I won't swear to it. The bigger effect is a wider spread to the score and higher grigne; you may notice a trend in the more recent photos at the link in a previous message.
I read that tip here, spritz at 5 minutes into the bake. It was attributed to Hamelman but I'm not sure I ever found it in "Bread". But it really seems to work well.
"Bread" is definitely aimed at professionals and student-professionals. It's not the best book for most beginners, but you could use it, gradually re-reading the more complex stuff after doing it less than optimally a few times. And there are home-baking tips scattered here and there, eg, Kitchenaid gets a mention along with commercial mixer types. And the yeast or levain section recommends 25% more for commercial-size formulas scaled down to home size.