Below is a proofed demi-baguette that was marked with lines spaced 1.25" apart. It is about to be baked without any steam as a baseline for testing the hypothesis that steam facilitates the stretching of dough. Since this loaf is not scored, we should expect it to blow out along the side. But still, if the surface stretches in response to internal pressure generated by the expanding CO2, then we will be able to observe and measure how much stretch there is.
Here is the resulting baked demi-baguette. The spacing between the lines is still very close to 1.25" indicating that there is little or no stretching when baked in a dry oven (this was baked in a combi oven set to hold the box humidity below 20% which effectively removes even the steam that escapes from the bread itself).
The photo below is another demi-baguette from the same batch that was baked with steam. It too was marked with lines spaced 1.25" apart before it was baked. This loaf had a defect on the top that allowed it to open slightly (actually the side-to-side dimension of the slit it almost exactly 0.25"), and the post-bake line spacing is very close to 1.375" except where the defect increases it to 1.625". So there is some small amount of surface stretching that seems to be facilitated by steam in the oven.
This loaf was baked in the same combi oven but with the steam generator and humidity controls set to maintain 100% humidity in the oven for the first 7 minutes of the bake (when it was just beginning to brown).
The photo below is another demi-baguette from the same batch that was slashed and baked with steam, illustrating the surface expansion that occurs when a well proofed loaf is slashed to allow the oven spring to open the loaf where you want it to split.
So the data indicates that the difference between having no steam and maximum steam is the difference between no surface area increase, and perhaps ~20% area increase even when there is no steam in the oven. It is a measurable but not significant effect. However, you can see the difference in color between the steamed and un-steamed loaves, with the steamed loaves having a more yellowish tone and a shiny surface (as opposed to a dull brown surface for the loaf baked without steam.
It is worth noting that this experiment has a sample size of 1 which does not imbue it with great weight in a statistical sense. But it does set expectations and will guide further experimentation. This particular batch of dough was mixed at 70% hydration, which is a bit higher than the 67% at which I would normally make baguettes. The objective was to build a fairly stretchy dough that I thought might be more amenable to surface stretch than a lower hydration mix. The next step up would have been 75%, but at that level it is ciabatta and I was not sure that I could put marks on the surface without deflating it.
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I need a second cup of coffee... just woke up to this.
A question: Was the top surface of the mini baguette resting or proofing after shaping on an absorbent surface (cloth, banneton) or uncovered to toughen the "skin" of the dough?
(I see some more experiments... a dough proofing under a wet cloth or oiled plastic wrap which are most common to cover loaf pans during proofing.)
Standard baguette process with a 70% hydration. 83°F dough temp, 20 min autolyse, mix 3 min at high speed, bulk ferment 1:15 with one S&F after 15 min; Divide into 6 demi-baguettes, pre-shape and rest 10 min; shape and set to proof (seam up) on a heavily floured hemp canvas, cover with light weight linen and a heavy Nylofume (nylon) bag. Proof about 2 hrs on the counter at 76°F.
Today with the 70% hydration dough they were pretty soft when I transferred the first 3 to the Teflon-coated perforated baking sheet (seam down). Both batches baked using a cycle of Preheat to 525°F, bake 5 min @ 460°F using high fan speed, then 450°F for 2 min at low fan speed, then 6 min @ 405°F at low speed/intermittent fan cycling. The dry heat batch was baked with low oven box humidity (20%) for the full 13 min baking time. The steamed batch was baked second (a few minutes after the first batch came out - just long enough to bring the steam generator up to temperature) and had the steam generator on at full power for the first seven minutes after which the humidity was reduced to 20% for the last 7 min.
The loaves were marked, measured, and photographed just before the pans went into the oven.
Here is the crumb shot of the demi-baguette that was slashed. The others were pretty tight except for the zones near the blowouts.
Unscored loaves with and without steam then a single scores loaf with steam. Is that correct . it would be interesting to see a scored loaf with and without steam. Maybe I can give that a whirl ...
One without steam followed by one with steam. Both the slashed and unslashed loaves were baked in the same batch. I did not slash the third loaf in the no-steam batch. In each batch one loaf was marked parallel to the length of the loaf, one was marked perpendicular to the loaf axis, and one was unmarked. There was no significant stretch along the loaf axis in either case so I did not include those photos here.
Thanks for your work.
Did you find a difference in the thickness of the crust between steam/no steam?. Also, what was the total flour weight for this particular batch?
Kudos on your highly detailed and science based posts, they help me tremendously in my quest for that elusive (and perhaps unattainable) perfect loaf.
Nino
Thanks Nino - I am still trying to figure out what is true and what is not. There remain many more "common knowledge" practices and "rules of thumb" that are bogus but have not yet been definitively debunked. I learned about 25 yrs ago that unless there was an experiment that I could perform to demonstrate that something was true, I need to reject non-academic pronouncements about the underlying phenomenology.
Crust thickness is determined by time and temperature, so to the extent that the oven box is perhaps at a little lower temperature while the steam generator and the heating elements are sharing the power bus, the precise temperature profile is not exactly the same as the no-steam case. But it is really pretty close. If you want a thicker crust you need to bake longer so that you remove water from deeper into the loaf. Of course you have to again balance time and temperature so that you don't produce briquettes.
The formulation is 26% pre-fermented flour, 100% hydration levain, 70% hydration dough, 2% salt, and 1560g total weight. That means 472g of levain, 399g additional water, 18g salt, and 671g of bread flour, which makes the total flour=907g and total water=635g. See the post above for the process details.
Thank you for debunking this one. It irritated me even back when I was baking rye breads. I would use the advice and then wonder... did I do it wrong? What happened?
I've been wetting my hands if I want a soft top, and adding water directly to the loaf that way. That seems to work much better. I've tried both scoring and wetting, and the scored area doesn't expand much. Note that it's gluten free dough at this point. I can no longer bake or eat gluten.
This is a little off topic, but have you tried brushing the top of the loaf with oil before it goes into the oven? Or immediately after it comes out?
Gluten-free doughs are really difficult to design and seem to be quite dependent on the exact mix of starches and hydrocolloids that you decide to use.
I hadn't thought to try that yet, thanks! I'll try it both ways next time.
Do let us know what works for you.
Here is a shot of the crust and crumb of a loaf that was baked in the local community wood-fired oven last weekend. Baking time was around 15 minutes and the oven was still really hot (as you can tell from the color of the ear). The other loaf from the same batch of dough was baked for 30 min (as part of the 4th load vs the 2nd load for this one) and had a lighter crust color but a thicker crust (no crust photos of that one).
Really appreciate your input Doc.
but it also promotes blisters in white bread, You were asking about blisters and my thoughts for white breads is that as the the skin gelatinizes under steam and begins to set and thicken it traps the escaping water vapor from below and continues to expand just enough to make bubbles especially if the dough is cold coming out of a retarded proof. The cold dough makes the water vapor escape later than it normally would after the skin in well gelatinized but still pliable due to the steam environment and really traps the water vapor. I think steam for the first half of the baking is the most important thing you can do once the dough hits the oven.
Happy baking Doc
I see a big difference between the blistering that I get when I retard vs what I get without it. I agree with you that the steam gelatinizes the surface starch and provides a gas-tight layer, but I can't rationalize why water would boil when the temperature of the adjacent dough is still relatively cool. The explanation I lean toward is that the blisters are made by CO2 that is forced out of the super-saturated solution by the rising dough temperature (since the dough stays fully saturated with CO2 as the temperature goes down during retard so long as fermentation continues). But alas I don't have the instrumentation needed to make a direct measurement. Since steam gelatinizes the surface of non-retarded dough even more quickly than for retarded dough, I would think that if the gas in the blisters is water vapor, it would form sooner in the non-retarded dough and we don't see that - in fact the blisters I get on non-retarded dough are quite small while the blisters on retarded dough can be quite large.
vapor starts coming off as whiffs of steam when the water is 140 F - not boiling. I'm pretty sure that it is the water that is right under the gelatinized skin that is turned into water vapor that causes the blisters not trapped CO gasses escaping the gluten matrix. Blisters only form with high hydration dough and the higher the hydration the larger the blisters
Also note that water in a bowl will vaporize into gas and evaporate at room temperatures but very fast in the 100 F AZ sun once the water hits 125 F
I suspect that the pressure required to form a blister is pretty high since the starting size is quite small, but I don't yet have the data to show that water vapor can't be the source.
More when I am better educated.
Sorry to be so slow on this, newish baker. Are you saying that the conclusion of the experiment is that steam makes minimal difference to oven spring, slashing is what makes the visible difference?
The claim is often made that steam allows the surface of the dough to remain flexible and thus stretchy in the oven which allows a loaf to expand to a larger volume before finally being stopped by hardening of the crust.
This experiment demonstrates (at least under specific conditions) that steam has minimal effect in facilitating dough surface stretching.
I think you can extend this to observe that slashing (as opposed to simply adding steam to the oven) does much more to facilitate dough surface area increase during baking. Slashing also effectively guides where the surface fractures and thus determines to a great extent the esthetics of the finished loaf.
No question that proper scoring can make all the difference. I can't remember the last time I baked without steam, but I have plenty of experiential evidence of good and bad results tied to scoring.
I remember my thesis days. Thanks for the information. They are very useful to eliminate confusion.
Thank you so much for the clarificaton. There are so many variables I find it hard to assess how to make my loaves better. I certainly have a lot of room for improvement with slashing. Working on tartine country loaves at the moment and not sure if it's to do with my clumsiness or maybe under/over proving that causes 'drag'. Good thing is that still delicious when not perfect. Thank you for all the expert input.
As a novice baker, it's very interesting to read this experiment of yours Doc. Most loaves that I bake go in the oven with a relatively thick 'skin' on them after a 24hour cold proof in the fridge, so I wasn't sure how steam would alter that. It's an interesting theory. Does any one know the origins of steam use, or why it came about in the first place?
Apparently it goes back quite a ways. It seems likely that the steam that naturally accumulated in wood-fired ovens was observed and perhaps emulated. The article linked below contains some interesting bits, but also is loaded with misunderstandings about what was going on. Adding steam might have been an attempt to cool off a wood-fired oven that was too hot to bake bread without burning the crust. And the unproven theory that steam facilitated oven spring seems to be equally old.
This link includes the full text of Report on Vienna bread, by Eben Norton Horsford of the United States Scientific Commission, published by the Government Printing Office in 1875.
https://books.google.com/books?id=6jRDAAAAIAAJ&pg=PA94#v=onepage&q&f=false
The problem is that other TFL readers are taking this as evidence that you don't need steam.
If you are attempting to be scientific then you HAVE to be scientific. A sample of three is nowhere near large enough to draw conclusions. You also need to describe the model of oven you are using. Oh, and then repeat the process with other types of oven. In other words: you need to apply the scientific method. Without the ability to replicate, this is anecdote not science.
Oh, and by the way, you have set up a straw doll to knock over. The reason dough is scored is to produce a line of weakness on the thickest part of the skin to allow expansion on the top of the loaf. Without that line you will get loaves that look like those is your photo regardless of how much steam you generate. That's because after decent shaping, the skin is strong enough to contain and restrict expansion and blow-outs will only occur along the base of loaf. Although you discuss them, skin strength and thickness are just two of the factors not scientifically accounted for here.
I seem to recall that Prof.Calvert repeated his autolysis experiment on hundreds of batches of dough whilst taking into account every variable he could think of. Because of his thorough scientific approach, we now understand how and why autolysis works. No one would have accepted his work on the basis of three loaves.
Perhaps it's time to do follow in Calvert's footsteps with your hypothesis? I'm afraid your conclusions are far too sweeping to be justified by the evidence so far. If want to justify using the term debunking, you have to do the job properly.
If you believe that what I have described is incorrectly interpreting the data, I have tried to include sufficient detail for you to replicate it as many times as you choose. It was not offered as a statistically significant sample size (in fact I pointed out the lack of statistical significance). I encourage you to re-run the case in your oven with your dough and your instrumentation, then report back here with your results and a detailed process description for the collective critique of those who are subscribed. The point was to provide a counter example to the claim that the function of steam is to keep the dough soft and stretchy during the early phase of baking and thus facilitate oven spring by allowing the surface to stretch more and more easily. The data show that the presence or absence of steam has no effect on the effective elasticity of the dough surface, and that slashing facilitates oven spring by providing a seam along which new uncooked dough surface continues to be exposed as the loaf expands.
I agree with you that Professor Calvel (not Calvert) had good process discipline and effectively used statistical methods to validate his theories. However, he did not (as is so often claimed) attribute the benefit of an autolyse step to proteolytic degradation of gluten proteins. As practiced in the modern baking industry, autolyse is generally a ~20 min delay between initial wetting of the flour and high intensity mixing. The autolyse delay of 20 min serves to hydrate the flour. It works whether the yeast/levain is incorporated before or after autolyse.
So, what's the purpose of the steam? If the purpose is to slow down the drying of the outer skin of the dough (and thus keep it pliable) then one way to look at it is via humidity. As we all know when it's humid out and we sweat, the sweat doesn't evaporate very well. Evaporation depends to a large degree on the humidity present. At some point (100% relative humidity) evaporation ceases because the saturation vapor density for that temperature has been reached. Well, the amount of water vapor that can be present depends on the pressure (constant for the oven) and the temperature. Higher temperatures can hold more water vapor before it becomes saturated. This means that if the oven is at a certain relative humidity to begin with cold, it will take more water injection proportionally to make a change in the humidity in the oven when it's hot.
So to get some data on this, I got some numbers from this table: http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/watvap.html#c1
At 68 deg F (roughly where the oven starts out) the saturation density of water vapor is 17.3 grams water/cubic meter. Since the kitchen is not likely at 100% relative humidity there is less water vapor than this in the oven to begin with. But also from the table, at 392 def F the saturated vapor density is 7840 grams water/cubic meter -- 453 times the 68 deg water. So it takes a lot of water to raise the humidity appreciably in a hot oven. What this says to me is that even with a lot of steam injection, the humidity in the oven wouldn't change much at all. So, unless something else is going on with the steam than to increase humidity, it doesn't appear it would make any noticeable difference.
I have observed, in a home oven that is well steamed, moisture condensing on the surface of the dough even though the oven temperature is 450F. Some of that condensate is absorbed by the surface layer of the dough and some evaporates. Both cases help to keep the crust softer longer than it would in a dry oven, allowing the loaf to expand before the crust sets.
In a steam-injected commercial oven, the steam is under pressure and displaces the drier air in the oven. That creates a water vapor environment, instead of a humidified air environment. The baker eventually vents the steam to permit drier air back into the oven after the first minutes of the bake. The effects on the crust are more pronounced than anything I can achieve in my home oven with steam at atmospheric pressure and continuous venting.
Paul
Paul,
Right, I was wondering about the condensation too. Since the dough is a lot cooler than the steam, there will be condensation at least for a time. So, what could happen is the local humidity at the surface of the dough could be higher for a bit. Also, some moisture might be absorbed. However, the question is whether enough would be absorbed and how long the condensate would stay. At 450 deg F, even with some steam injection, the relative humidity in the oven would be very low. For instance, if the initial humidity was 50% at room temperature, at 450 degrees the relative humidity would be less than 1 percent. Even an injection of a cup of water would only raise the humidity a couple of percent. So, evaporation will occur very quickly. It would be interesting to know how long the condensate stayed on the surface. So, if that is what's helping then it could make sense to just spray the dough before putting it in the oven and not worry about steaming.
The air, per se, in the oven isn't a factor for humidity. It depends on the amount of water vapor present relative to the saturation water vapor amount. So even if the pressurized steam displaced the lower humidity air in the oven, that really doesn't do much of anything for the humidity at 450 degrees.
Edit add: Also keep in mind that the dough at the surface would have to stay hydrated and pliable long enough for the temperature inside the dough to increase sufficiently to cause rising. My guess is that what keeps the dough pliable is not the humidity in the oven but the steam escaping from the dough as it heats.
The point of this experiment is to show that once it starts to cook, the dough surface is not very pliable at all (beyond about 3-4% strain) and oven spring depends on either a slash or a blowout to allow volume expansion to create the needed additional surface area. Pan bread does retain some degree of pliability at the dough surface next to the pan which seems to account for the "rise" since the pan shields the dough from the heat of the oven long enough to accommodate the majority of the volume expansion associated with oven spring.
Paul,
Almost exactly two years ago I did a short paper (really to feed my own understanding) that I posted here. It addresses this issue as well as some ancillary factors that affect how different ovens exploit different heat transfer mechanisms. You have to read down a few paragraphs before phase change phenomenology is dealt with, but please let me know if there are other/additional questions.
Doc
Doc,
Very illuminating paper! Thanks. So the steam is important for crust formation. Good to know. I have a question. What do you think is going on with the water vapor generated in the dough. Obviously, it somehow escapes since the loaf weight decreases. My thoughts have been that as the water boils and creates steam, it and the CO2 create pressure and migrate based on the weakness in the dough. When they get trapped in a stronger section, they create an open crumb there but the steams somehow escapes anyway. What makes it even more complex, I think, is how the heat moves from the bottom (for loaves baked on a stone or steel) and the sides of the loaf inward. So, as the outside gelatinizes and then hardens it would seem the pressure moves toward the center. In other words, what do you think is going on in the dough internally as it cooks that might inform things like hydration and dough handling? If the goal is open crumb, would it be better to not try for a homogenous structure? Or maybe even try to create faults in the dough with types of folds or a tiny bit of flour during the folding process?
The water in the dough stays as liquid water, but is driven by diffusion to the surface of the dough where it evaporates and takes heat from the surface layer. The alveoi (bubbles in the dough) are initially very small (microns in diameter) and inflated with CO2 that diffuses out of the liquid phase of the dough - which is saturated with CO2 from very early in the process as the yeast shift from aerobic metabolism to anerobic fermentation when the initial atmospheric O2 is depleted. After that the cells grow by merging and collapse. The openness of the crumb is determined by how this collapse proceeds. CO2 generation and migration are governed by a bunch of factors (diffusion, surface tension, saturation pressure). But CO2 expansion (Boyle's Law) drives oven spring almost exclusively. The claim that steam contributes is another wives tale since the crust is the only place where the temperature gets above the local boiling point of water, and it is dry by then. The other claim occasionally put forward that alcohol with its slightly lower boiling point somehow contributes to oven spring is not supported by any data that I am aware of. There is not enough of it (it stays in the crumb, escaping after the crumb has set - mostly during cooling), and there is plenty of CO2 to fully account for the volume increase. The best/most convincing demo of that requires only a bell jar and a vacuum pump. If you put a fully proofed roll in the bell jar and turn on the pump, without any heat addition at all, the dough will blow up to magnificent size. And then collapse when you release the vacuum. It made me think about building a vacuum oven to preserve/enhance the effect.
As for the heat transfer from the oven to the core of the loaf, it is exactly solved by the 3-dimensional heat equation.
Hmm. So why does higher hydration seem to promote more open crumb? Is there more CO2 produced? Also, I would guess that as the dough heats from the outside in, there would be temperatures above the boiling point of water. I mean if the final temp in the middle of loaf is 200+ degrees, then much of the outer dough has been well above the boiling point.
Cell growth in bread dough is complicated, and not well modeled. There are some folks in France who have used a high flux particle accelerator beam line to do rapid and very high resolution CT imaging of proofing bread dough. Somewhere I have filed one of their reports, but I don't find it immediately.
And yes, some point in the baking loaf the temperature does get above boiling. But the boundary is at the inner edge of the crust and you can locate it quite easily by looking for the color transition from the white of the crumb to the lightest shade of brown (which is due to the Maillard reaction). But by the time the crust is hot enough to begin to brown there is not much water left. And everywhere from that point to the thermal center of the loaf is at a lower temperature. It is a difficult experiment to run but people have embedded very small thermocouples in the outer regions of a loaf and then baked it.
The notion that the condensing steam was delivering heat to the bread had entirely escaped my notice, though it shouldn’t have. My physics instructors, if they are still alive, would not be impressed.
The other obvious but overlooked point is that expansion occurs at breaks, deliberate or otherwise, in the crust. It is then the crumb expanding under the crust that shoulders the crust aside. Right there in front of me but not acknowledged.
Thanks Doc.
Paul
If you have not seen this, it might provide some additional insight.
It took multiple runs to get the lighting right, but it was worth it.
Point for reference, according to your numbers (7840 grams of water per cubic metre at 392°F): To achieve that saturated vapour density in a 5-cubic-foot home oven would require about 1.1 litres of water, assuming none of it escaped.
Right, and it's even worse than that because the curve for saturated vapor density starts to go asymptotic (a small change in temp results in a large increase in vapor saturation density). So at 232 deg C (450 deg F) the slope would be very steep.
At 200°C and 1 atm pressure, the density of steam is 460g/m^3 (according to the steam tables I consulted). I don't know where I implied that the vapor density was 7840 g/m^3 at 200°C
My bad. I apologize for misleading anyone. I was misunderstanding the charts I was looking at. It's been too many decades since I studied thermodynamics.
You don't actually need a lot of steam; in a deck oven, steam injection only lasts for 10-30 seconds. Incidentally when the steam gets into the oven, it is pretty low pressure, partly because lower pressure steam is wetter and also if it was at high pressure, it would probably blast holes in the loaves. But there will be a good flow of steam, with multiple injection nozzles.
With my self built external steam generator, I steam for 2-3 minutes and that's enough - you can see the condensation on the surface of the loaves in the oven.
The thing is that once the steam is in, you need to keep it there for 10-15 minutes. I think a modern deck oven will be pretty well sealed and the vent is opened to vent the steam after the 10-15 mins. A home oven tends to leak steam pretty fast through the (non-closable) vent. This is why methods such as Sylvia's steaming towels work well, because they keep producing steam as it's lost.
Lance
Lance - I agree with you, and I suspect that once you have supplied enough steam to fully gelatinize the surface starch, you probably don't need any more steam at all,and could logically vent if you had a reason to. I ran a couple of experiments showing that that steam in the oven (and most certainly water on the surface of the dough) slows down the Malliard reaction and inhibits browning, so at some point I suspect you want to vent if only to enhance browning.
I have observed that electric ovens are often relatively well sealed (and my electric combi is quite tight so long as the butterfly valve on the vent is in the closed position) but gas ovens are, as you note, subject to flushing the steam out through the vent along with the combustion products.
What is the current configuration of your external steam generator?
Well Doc, my external steam generator is a stove top pressure cooker, modified to have a valved take-off point, with no modification to the safety devices, before anyone asks.
This feeds into the oven via a flexible hose. Inside the oven the steam is piped to the back of the oven where it is injected via three nozzles.
I would go so far as to say that it works extremely well, with no messy towels or lava rocks, but my wife did wonder why I was drilling holes in the side of the oven and the kitchen cabinets!
Lance
Redundant post
A clean mod to the oven that does not interfere with any primary functionality. And the flow is all downhill so that the condensate that forms in the flex line has a chance to be revaporized without becoming trapped somewhere in the plumbing. What was the flex line originally designed for? And what is the liner material to assure that it doesn't melt below ~300°F?
Nozzles at the back where the convection flow will pick up the steam and distribute it fairly uniformly. Burner looks like 12-16K BTU/hr so ~ 4KW equivalent which is probably about what the oven does, so if the net efficiency (burner + pressure cooker + plumbing) is 40% you effectively increase the input power by ~40% when the steam generator is on which is nice.
Definitely something I would consider.
I found a good quality shower hose to be perfect as the flexi, especially as a I had a spare in the parts bin.
Chrome plated solid brass spiral outer encasing a length of silicone tubing. Never under pressure in my design, so that's not an issue.
Not to be confused with other versions, which might be made of vinyl, and which would melt.
Yes, the design does not affect normal use of the oven at all and does not reduce the available space, once the kiln shelf is removed.
Lance
just not sure how to formulate it.
I have observed with my slow heating (no stone) electric oven that when it hasn't heated up to 230°C and I have put the bread in at say 175°C to 190°C with no steam, I get a nice rise as the oven continues to heat toward 230° C.
Could this imitate what steam tends to do; that is; cool the oven and let the heat rise somewhat gradually with the oven spring?
I am aware that there are ovens that tend to blast heat while preheating possibly burning crusts but mine doesn't and seems to have an old temperament. I'm also asking, is the energy wasted in a household oven to overheat the oven to say 250°C cool it down with steam, vent and let the oven temp rise again?
Maybe the addition of steam is to temporarily cool down the oven for a gradual rise in oven temp moreso that what steam actually does for the bread.. It might be difficult to toggle a large bakery oven. However in a home oven....this is not so difficult.
Mini o economizing. :)
The steam serves a different primary purpose (very rapid heating of the dough surface through condensation of steam at 100°C directly on the surface of the dough) and only incidentally acts to cool off the oven. If you are not seeing comparable oven spring when you wait for the oven to fully pre-heat, then I would suspect that the thermostat is not very sensitive and the oven is cooling off quite a bit before the heating element is switched back on. Some ovens see 50°C temperature swings between thermostat turn-off to turn-on. By loading your dough before the thermostat turns off the power to the heating element, you get the early heat that you need and are not getting otherwise. A convection oven dramatically reduces the impact of a large thermal hysteresis, but is not a substitute for a sensitive thermostat.
This is a case where a pan of lava rock can help (in two ways). First it stores heat to make steam quickly when you add some water. Second, the steam will tend to more quickly drop the oven temperature so that the thermostat turns the heat back on. All while the steam is condensing on the dough and doing what it is supposed to be doing (hydrating and gelatinizing the surface starch). In a small oven, it is probably best to overheat somewhat just to get the oven surface temperature up to where radiation can augment convection and condensation of steam to deliver early heat to the dough. But you will benefit a lot from some added heat storage mechanism in the oven cavity (stone, tile, lava rock, steel plates, ..) which is charged up by the initial temperature overshoot during pre-heat.
because there's no real scientific literature that I can find on the subject, and Modernist Bread seems to agree with you. They declare steam helping with oven spring to be a myth after listing a few tests they did. Unfortunately it's not presented as comprehensive data, it's just a small paragraph. I'm gonna be re-reading this thread a few times to take it all in, I really appreciate what you're doing.
If you have not come across it, here is a link to a short piece I wrote on home oven heat transfer:
http://bit.ly/2PGyPbB
I did it for myself but others have found it useful.
Doc, did the first loaf (baked without steam) and the second loaf (baked with steam) bake under the identical conditions (time, heat) with the exception of steam and no steam?
I have read this post completely many times, and like other post of yours, I pickup something new most of the time.
If, and I believe they were baked under identical conditions with the exception of steam/no steam, it seems evident that the steam doesn’t increase stretch in the crust. It is also super interesting to me how much more browning the steamed baguette attained.
Danny
Doc, it is difficult to believe that neither of the first 2 bakes didn’t expanded over all and increase the width of the lines, before blowing out at the bottom. At 70% hydration you mentioned, they were a little loose. A ballon would expand in all directions before bursting in a small area.
I see your results, but they are puzzling to me. I am interested to hear your reply.
Danny
”inquiring minds want to know”
I had not noticed the difference in browning, but yes they were baked using the same computer-controlled cycle, except that the one without steam had the box humidity set to zero (though it cant actually hold it at zero).
The pale loaf compared to the browned loaf convinced me that the steam does in fact great enhance the cooking of the exterior of the loaf.
But, please speak about the inflation. You said that the 70% hydrated dough was soft when shaping. Let’s say the steam has absolutely nothing to do with softening the skin as indicated in your test. Still wouldn’t you expect that the whole dough would expand some before enough internal pressure forced the dough skin to breach, in this case at the bottom. How can the fact that it didn’t spread between the lines be explained?
Danny
I could be considered a type of "doubting Thomas". After reading Doc's test and hearing claims that steam does not facilitate the stretching of the gluten skin during baking, I had serious doubts. Common sense (which at times can be misleading) lead me to believe that steam would settle on the skin and keep it more pliable for a longer time. Because the skin remained more pliable, it is reasonable to expect that as the humid skin stretched, the oven spring would be larger. And everybody wants more spring...
The good news and the bad.
Although steam does not make the dough skin more stretchable, it does gelatinize the starch on the skin. This seems to “seal” the skin. It becomes more air tight. You can actually watch as the skin starts to shine on the doughs with additional steam. The inflated gasses can not escape as easily. I think this is why we get better oven spring!
Another benefit that may not seem so obvious, is the fact that steam causes the skin to brown faster. As the skin browns, it becomes gradually harder. When properly timed, the hardened crust will cause a fracture near the score line and produces those desirable ears that we all strive for.
For a better viewing experience, use this link.
Tip - did you know that YouTube has a function that will allow the viewer to either speed or slow the playback speed of a video? To utilize this function click on "Setting", located in the YouTube video screen and choose "Playback Speed". There are a number of options. Slowing down the Playback Speed is an excellent way to study a video and obtain much more detail.
By-the-way, Doc is right...
Danny
Clearly, if you allow the loaf to continue to proof, the dough will increase in volume which requires that the surface stretch to accommodate the volume increase. But as you raise the temperature, there is some limit above which the yeast is killed and the dough can still stretch. I suspect it depends on the humidity, but when you put a loaf into the oven and the oven is cold, and then you turn the oven on, there is a period of time during which the loaf can expand, and the surface will stretch. Then at some point the surface cooks and transforms into a constraining membrane that must break before additional surface area can be created by volume expansion. The question is "what is that point?". Between the point where the surface area stabilizes and the point where the surface breaks, the loaf continues to expand and tends to become spherical (even a baguette is attempting to become a sphere, but in fact is limited to making a cylinder with hemispherical end caps, even if you are perfect at shaping).
I love your scientific tests, both Doc and Danny. Especially love the video documentations.
Forgive me if I misread a post, but I feel like I'm still missing a key piece of data in this steam testing. Doc didn't include an unsteamed, scored dough, and unless I'm wrong, Danny repeated the same. I think we're agreement that scoring directs where the expansion occurs and thus gives us control over the final shape of the baked loaf -- both of your tests demonstrate that. But to see what steam actually is or is not doing, we should test how steam affects a scored dough. (And by "we," it's not the condescending royal plural here -- I do mean "we" including me and anyone else taking part)
Some more Devil's Advocate here, for sake of rigor: I'm not sure if the two parallel sharpie marks on the top are an accurate measure of whether or not steam keeps the skin pliable and able to expand more. First, in your unscored loaves, the distance between the two lines didn't significantly change with or without steam, but that could be because the main expansion didn't happen there. The blowouts pricked a hole (pun intended) in the test's ability to measure the intended area (the two lines on top). Also, even if there weren't blowouts, maybe the top isn't the best area to measure. Danny's profile angle of the oven clearly shows that both loaves do increase in volume, so instead of measuring the tops, maybe the marker lines should been along the side -- or better yet, measure the circumference around the equator. But an unscored dough will still have the blowout issue.
I'm interested in seeing how steam or no steam affect a scored dough's overall oven-spring. I do find Doc/Danny''s argument intriguing (if I understand correctly) that steam actually hardens the outside faster, and thus combined with scoring, directs the expansion upward for maximum oven spring. But I'm not sure it's completely debunked yet about steam helping to keep the skin stretchable in the early part of the bake and contributing to oven spring volume. Both ideas could be correct, just at different times in the bake.
I know I'm late to this thread, so forgive me if this is already moot and I'm just not caught up yet. I'm going to start documenting my own experiments better in order to contribute.
--Steve.
Welcome to the discussion, Steve! As far as I am concerned these discussions are always open and eager to take on new thought.
Speaking for myself, and I think Doc, we are always open any testing or experiments that may refute our findings. If you read enough of my post you will see me write, “this is what at think at the present time”. The truth never changes but our understanding and pursuit of it does. I live by the statement that, “the truth sets us free”. Often we get other bakers critiquing our test and experiments and that is fine. But it is refreshing when we find someone who is actually willing to test further. Please test and share your findings.
You wrote, “ I do find Doc/Danny''s argument intriguing (if I understand correctly) that steam actually hardens the outside faster, and thus combined with scoring, directs the expansion upward for maximum oven spring.” At this time it seems to me that the steam does not assist the stretching of the dough as I once thought. But I think I learned the steam does cause the temperature of the crust to rise quicker. Once the crust heats it begins to brown and once it begins to brown, the crust hardens. If the crust is to fracture, in order to form the ear, it seems necessary that the crust lose some of it’s stretch (harden). The timing of the hardening of the crust is also very important. It must coincide with the expansion of the gas. If the crust hardens after the oven spring the bread is apt to have a nice bloom but fail to produce an ear. This is where the benefit of the steam takes place, I think.
Take a look at some of these time lapse videos and share any new observations. It is nice to have a new pair of eyes n the project. I can’t explain how much I learned from these videos. http://www.thefreshloaf.com/node/61659/ear-bloom-and-oven-spring-skin-deep-beauty
Danny
Danny,
"I live by the statement that, “the truth sets us free"
I agree but I really like Gloria Steinem's similar quote:
"The truth will set you free, but first it will piss you off" :-)
Haha...
I keep a mind set of humility. Life has taught me that. When I was young I thought I knew everything. But didn’t have the intelligence and life experience to know that I knew very little. I study a lot and therefore have loads of opinions. But I know some of them are wrong. The problem is, I don’t know which ones they are :D
Right. Living life can have a way of slapping down any arrogance. Here's a distilled quote from Donald Rumsfeld:
"There are known knowns. There are known unknowns. And there are unknown unknowns."
I think when it comes to bread making for most of us the later two far outweigh the first. But I think that can be why bread making can have a life long appeal. There's always something to learn and try.
The lack of a scored loaf without steam is indeed an omission, and something that is relatively easy to remedy. How about you do the experiment with no steam and a scored loaf beside an unscored loaf? You don't need to make a movie but it would be a good idea to take before and after photos against some kind of background that would provide an ability to quantitatively compare the before with the after. However, I would note that the wives tale claims that steam allows the dough to expand without making any claim about what lack of steam does. So a run without steam, while potentially filling in a hole the matrix of experiments, does not address a hypothesis being tested and thus has no possibility to prove or disprove anything. Which is why it was omitted. But I would be interested in seeing a good comparison.
Consider the following experiment which I think provides an analog of the outcomes observed: Take an empty balloon made of two 12" diameter circles of 0.002" thick Mylar joined at their outer perimeter, with a port installed somewhere to allow inflation with air. Now draw two parallel lines on the surface that does not contain the inflation port. Now inflate the balloon. Mylar is VERY strong (about 25,000 psi) and while it stretches as much as 100% before it fails, the required pressure is pretty high (about 30psi in this case). So what is the behavior that you see between the empty state and the point where the surface might show some stretching? And what is the distance between the lines drawn on the surface? Until the internal pressure reaches 1 atmosphere, there is no possibility of surface strain since there is no differential pressure across the membrane. The height of the balloon goes from essentially zero to the point where height and width are equal. The surface area of the balloon is equal to the area of two 12" circles (~226 square inches) which does not change until the internal pressure rises to the point where the surface begins to stretch. As balloons tend to do, they minimize the ratio of surface area to volume which in this case produces a sphere with a surface area of 226 square inches. Such a sphere has a diameter of 6/sqrt(2) or ~4.24", but it is as tall as it is wide. After that, as you increase the inflation pressure, the surface expands until if fails somewhere.
For a piece of dough, exactly the same thing happens (except that dough is quite weak relative to polyester), it expands uniformly, tending to become a sphere if the surface does not stretch before reaching that point. A boule matches this behavior best because the tension is fairly uniform everywhere while a batard or baguette tends to approximate a cylinder with hemispherical end caps and fails somewhere along the cylindrical surface because that is the high stress area. It always fails where it has the least ability to resist, someplace where there is a weak spot or a defect.
In the case of the dough piece that was not slashed (see photo), the surface area stretched a few percent and was strong enough to resist the internal pressure until the starch was strong enough to hold the shape of the loaf and it was fully cooked, at which point the internal pressure is relieved by leakage of the trapped CO2. As is visible in the photo, the defect that allowed the surface to fail facilitated a small local surface area expansion and a crack that opened by a small amount.
The only residual question might be what is the tensile strength (and modulus of elasticity) of the dough surface with and without steam. The evidence is that there is not much difference, but if you can measure the surface area increase under the two conditions we will have a better estimate than zero. So I encourage you to help us out by performing the experiment and reporting back on your results. I expect that the unslashed loaf surface area will expand by a few percent while the slashed loaf will manufacture new surface area at the slash as the loaf expands, perhaps as much as 15% if the dough is well developed, carefully handled, and properly proofed and baked.
Thanks for the welcoming replies, everyone. Danny, I've binged your videos -- I love your scientific explorations quite a bit as I've shared some of those same questions. Even more than that, I appreciate your growth mindset of not taking everything just as gospel without evidence.
Same for you Doc -- I'm slowly making my way through your papers and posts as well.
Like you guys, I had plenty of questions when I dove into the sourdough pool 2 years ago. And some were about certain "givens" that people kept repeating without explanation.
Doc, I was especially curious about your "what causes oven spring" investigation with Emily B and wished the x-ray test would've worked. Because even now, there's something that still bugs me:
Claim: We want to transfer heat to the dough as quickly as possible when loading the dough into the oven. Hence, pizza stones and large thermal mass Dutch ovens. AND steam, which transfers heat much quicker than dry air.
But why? This might be a tangent, but part of the same steam discussion. I've had equal results using heavy Dutch ovens as using disposable aluminum roasting pans -- the important part for me is making sure they are sealed (closed systems)(I use a gas oven that won't hold in steam). And then there are folks who have experimented with cold Dutch ovens and un-preheated ovens. So what exactly is happening during the first part of a bake that allegedly needs fast heat transfer? Like Doc, I don't buy the factor of yeast giving one last burp, otherwise why not go for slow heat transfer to give yeast a longer burping time?
I've experimented with the cold starts myself, and haven't noticed much difference. Then again, that was before the gauntlet was laid for me to start officially documenting and reporting.
Looking forward to all of your folks' wisdom.
Steve, when you mentioned, “ I've had equal results using heavy Dutch ovens as using disposable aluminum roasting pans” I thought about this test. It may interest you.
http://www.thefreshloaf.com/node/56822/cast-iron-cooker-vs-graniteware-thermal-data
Thanks. I hadn't seen that thread. I've settled in on a graniteware lid over a thin baking sheet for one of my setups. Because they're so thin, they heat up very quickly, so no oven preheating needed. Only caveat is that I have to put it towards the top rack of my oven or else the bread bottom might burn. I usually do a combo cooker on the bottom, and the GW/baking sheet on top.
Steve, when baking with a graniteware cover, I almost always bake on a preheated stone with the cover only.
I have a stone that was cut for my oven. It has a 2” space to the wall on all 4 sides. Where most people say there 650 gram loaf bakes in 35-45 minutes mine consistently bake to an internal temp of 206F and higher in 22 minutes. maybe it’s the stone and/or maybe the fact that I don’t vent my electric oven. I’m not sure.
Where did you get a custom-cut stone? Was it originally a baking stone, or made for another purpose?
https://bakingstone.com/order/
I’ve had it for years and am completely satisfied. I tried a baking steel and went back to the stone.
It has been a long time since I had a gas oven, but others have reported that you can add a stone/tiles on a high rack to get some more thermal mass into the box, put your stone on the bottom with a couple of layers of (crumpled and re-flattened) heavy foil under it (so that it mostly heats from the top), then after you load your dough and your steam generator, shut off the oven and plug the vent for 5 or 6 minutes. After that, unplug the vents before you reset the oven to whatever temp you want to finish the bake. Control how long the steam lasts by how much water you put in the steam generator. Terrycloth towels draped over a rod with the bottom edge in a pan of water wicks up a lot of moisture and has a very large surface area exposed for evaporation. But you need to pull the terrycloth at some point or it too will brown. 100% cotton is good to 400°F, not 500°F.