The Fresh Loaf

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dabrownman's picture

After my future son in law brought me a beautiful loaf of Acme SD from SF this week. Lucy decided to make one of her own that she thought would look better on the inside and taste lot better too – the two areas the Acee bread was a bit lacking.

Wow you can really tell the 4 different grains here!

I also missed Lucy’s 13th birthday the week before when I was visiting my Dad after his knee surgery.  She was not happy about me being gone but life gets in the way of celebrations sometimes and I am happy to note that my Dad’s recovery remains on track.

The bran levain is s much darker than the dough flour.

Lucy was hoping I would bring her a pet raccoon from the Ozark mountains of Southern Missouri but we couldn’t quite get the one living under his shed trapped and every time it came out I wasn’t quick enough getting to the .22 rifle to bring Lucy home a pelt either.  So poor Lucy didn’t get a present this year except for this bread and she doesn’t get any of it to eat either!

This is a simple formula, as far as formulas go with Lucy, like most SFSD breads tend to be.  The levain was a 2 stage, 12 hour. 100% hydration, 12% pre-fermented sprouted grain one where all the bran from the sprouted grain was used for the first stage and the high extraction sprouted grain was used for the 2nd stage.   Once the levain doubled after the 2nd stage, it was retarded for 24 hours to bring out more sour notes.The 4 sprouted grains were rye, red wheat, spelt and Kamut and the overall sprouted grains came in at 20% making it a healthier and heartier SFSD white bread variety.  The overall hydration was 80% with the 80% white flour being LaFama AP and Albertson’s bread flour both of which were on sale this week for $1.49 and $1.79 for 5# bags at the grocery store. The 2% salt was pink Himalayan sea salt.

We did a 1 hour autolyse with the salt sprinkled on top and we did a double hydration with 2% water going in with the levain before the first set of 40 slap and folds.  We then did 2 sets of 10 slap and folds and 3 sets of 4 gentle slap and folds all on 230 minute intervals.  The dough has risen about 40% when we pre-shaped it and then shaped it into a squat oval.

We plopped it seam side up into a rice floured basket and bagged it in a new trash can liner for 14 hours of retard overnight.  When we took it out of the fridge we fired up the oven to 500 F with the Combo cooker inside.  Once hot we un-molded the dough onto parchment on a peel, slashed it 6 times, cross hatch style, like the Acme bread and put it into the oven as we turned it down to 425 F – the supposed temperature used at Larraburu.

Killer bruschetta using heirloom cherry tomatoes from the back yard and that Acme Sourdough bread.

It helps to have a nice sourdough blueberry pancake breakfast on bake day

Since the dough was cold I upped the stem period to 24 minutes from our usual 18 to make sure that the dough had enough time under steam to spring.  We were hoping, since it was a whitish bread, high hydration and cold, that it would blister nicely under steam as the crust gelatinized it would trap the water vapor from below to cause blisters right under the skin.  That is Lucy’s thinking at any rate and she is sticking to it!

It did spring and bloom explosively under stream, showing it was a bit under proofed and there were quite a few blisters too.  Once the lid came off we turned the oven to 425 F convection to brown it up which it did nicely.  We took it out of the oven when it read 209 F on the inside.  We will have to wait to see what it looks like inside but the outside was not quite as nice as Acme’s perfect 10 score that we gave it earlier this week but this one was close at a 9.

The inside of this bread is what SFSD is all about.  Even though it had 20% whole sprouted grain the crumb was very open.  It was also glossy, soft and moist.  The best part is that this bread tastes terrific - fantastically delicious.  My future son in law says that this bread is hands down way better than the Acme loaf he brought me - even when it was as fresh as this one. We ate a quarter of the loaf straight away as part part of cheese, tomato, bread, fruit and melon plate as an appetizer with a nice glass of red wine.



12% pre-fermented 4 sprouted grain flour, 2 stage, 100% hydration, bran levain retarded for 24 hours.


8% high extraction sprouted 4 grain – Rye, spelt, Kamut and red wheat

40% LaFama APp

40% Albertson’s bread flour

80% water - overall hydration

2% PH Sea Salt

Lucy reminds us to never for get the salad!

Skibum's picture

This is my liquid levain version of Peter Reinhart's soft pull apart dinner rolls. I really enjoy the soft texture and the flavour that the honey brings to the mix.

I baked this time on parchment on a cookie sheet, so the rolls could grow to their natural roundness, rather than sticking together as was the case last bake.

Prior to baking I gave them 2 coats of egg wash, waiting a minute in between coats. I baked @ 350F for 15 minutes with steam, then another 14 minutes no steam. Great results once again, with great flavour and a shred able crust!

Here is the recipe:

68g liquid levain

236g milk scalded and cooled to below 90F

363g strong bread flower

1/2T kosher salt

39g honey, I slopped a little more

43g melted butter, again, I slopped a little more

1/2 large egg, or 25g egg

The left over half egg supplies the glaze before baking.

Happy baking friends! Ski

alfanso's picture

Yesterday's bake was a dry run to see what's what.  Today corrections were made, and hopefully for the better.  This time I used a spring pan which had a slightly wider base than the Angel Food pan, and also employed a small bowl in the center in order to enlarge the hole in the crown.

Otherwise everything else was business as usual.  And although this didn't get quite the loft and open score of yesterday's bake, some of the loft issue may be related to the crown being a little wider in diameter.  I think that overall I'm more pleased with the look of this one.  

1250g x 1 corona

IceDemeter's picture

So, there I was last Thursday with two fine loaves for all of the sandwiches that I'd need for a busy weekend out of town, a container of "issues" in the fridge, and a lot of questioning on the strength of my poor old NMNF starter.  Well - the husband managed to do some neck damage, which cancelled the plans for the weekend (and cancelled the need for so many sandwiches!), and left me with some actual time on my hands.

Besides the "issue" in the fridge, I also had been pondering the idea that I have been under-fermenting and under-proofing all of my loaves out of some kind of paranoia that going over was the ultimate unrecoverable error.  That this paranoia was sheer balderdash was proven by dabrownman's still-really-good-even-though-way-overproofed 100% WG bake, so I figured that maybe this would be a good time to experiment.

Friday had me feeding and babying that container of "issue", and by dint of getting it really nice and warm and feeding it up, I managed to get it acting fairly lively by the end of the day, and it was looking even better on Saturday morning.  The only problem was that I had so very, very much of it...  

I took the weight, figured that I didn't want to go more than 25% pre-fermented flour, and did a quick mix of 15% rye, 10% spelt, and 50% AP flour that would add to the 25% rye in the "issue levain", and started working with it, getting to a comfortable 75% hydration and kneading it to full windowpane.  I put it in a large clear container for the bulk ferment, and had it in the oven with the light on and the door open an inch (which gave me about 83 degrees F) and I let it go until it had fully doubled (which I have never done with a partially whole grain mix - never more than 30-50% increase) which took about 5 hours.  

While it was fermenting, I got this "brilliant" idea that I should do a loaf with half of it and then do rolls with the other half (since I had the perfect amount for 12 x 90g rolls --- and I have NEVER managed a successful bake of lean dough rolls).  The dough felt pretty good when I dumped it on to a damp work surface, preshaped half in to a quick batard and covered it to bench rest, and then started scaling out the rolls.  I got them all measured out, and then used a light dusting of flour on hands and bench to lightly shape them and put them on to parchment covered baking sheets to proof.  They needed to be covered, so I used some floured plastic wrap that I have frequently used over loaves (I keep it set aside for this), and then got the loaf shaped and in to a parchment lined banneton to proof.

Well - I let them proof, and proof, and proof... and got to the point where there was finally some visible rise in the loaf and a bit of enlargement in the rolls, so fired up the oven.  I figured that the rolls should go first --- aaaaand found that the flippin' wrap was fully and completely stuck to each and every roll.   Well, drat (not the word - but you get the idea).  I used the scraper to get the wrap off as well as I could, but things didn't look good at all.  Ah well - in to the oven with them!  I had a baking steel preheated in the oven, and a couple of empty tins (no lava rocks yet) heated, and had blocked the oven vent, so had the husband carefully pour in a couple of cups of boiling water to try and get some steam going,  There wasn't a LOT of oven spring, but there was some at least --- and I could see that adding the lava rocks could be successful for future tries.

While they were baking, I was watching the loaf, and I got to actually see as it tipped over the edge in to being over-proofed (it started deflating quite slowly, almost like a balloon losing the air).  It actually is kind of sad and pitiful to watch...  It was just a few minutes from that point to the oven being ready, so I tried scoring (oh, dear, how sad) and got it in to the heat.  It had some minor oven spring, but more sideways growth, and the scoring barely opened, but the crumb was surprisingly light:


All in all, I ended up with a truly ridiculous amount of bread for two people.  It all came out tasting wonderful, so it has been carefully wrapped and frozen and we are working our way through it, but there is no way that I need to bake this week!

That is just as well, since I have dedicated this week to getting a hearty and happily refreshed new round of NMNF ready to be stashed back in to the fridge, and the sad last remnants of the Feb and Mar versions can go in to the "discard" bin and get baked in to some muffins or biscuits or scones or something.  It has taken a few days now of keeping it warm and fed and cranking out new levels of yeast, but I finally have it truly zinging along now.  It more than doubled in less than 2 hours after the last feed, so it's now time to thicken it back up to 67%, and put it back in to it's slow cold snooze.   It's amazing how satisfying it is when your starter finally looks like this:

There's enough for me to try freezing some of it, and enough for a fully matured levain to just wait in the fridge for me to be ready to use it next week (if we manage to get through all that I made last week)...  'Til then, I'll be gratefully living vicariously through everyone else's bakes and blogs!

It is fairly typical that things don't go as planned, but the baking and the playing and the experimenting has still been a source of fun and happiness.  As a bonus, I am starting to learn not to be afraid of over-proofing, and have a much better feel for what my dough should look and feel like at various points in fermentation (and will be letting them go longer than I used to --- but hopefully not over the edge again!).  I also learned that I can get steam generated (and that I really need to get lava rocks - if only I didn't loathe shopping!) for baking things that can't really fit in to my trusty roaster.

Thanks for all of the encouragement, support, suggestions, and inspiration --- and keep baking happy!

IceDemeter's picture

It's been "one of those days" for the past couple of weeks, for weather (barometric pressure and temps all over the place), for scheduling, and for baking.

I started last week with the intention of doing a three-stage levain build out of 10g of my rye NMNF starter and then letting it retard in the fridge for a day or two.  I was in and out of the house and not really watching what was going on with it, but hadn't been too surprised when there wasn't any visible growth after the first feed, but was quite shocked that there was no signs of life at all after the second feed.  Following SOP, I discarded the amount of the second feed, repeated it, and went to bed, assuming that it would be fine over night.  

No joy in the morning, though --- no signs of life at all, although it didn't have the "wet flour" scent that I get out of an autolyse, for instance, but instead had that sour / tart / acidic scent of a well-aged starter.  I had no way of knowing whether it was the main starter that was the issue (it's been in the fridge since Feb 10, so it's been a while), the flour (it was freshly ground whole rye, but maybe I went too fine / too fast and over heated it), or the water (I always use filtered tap water that has been sitting out for at least a few hours to dissipate chlorine --- but it is spring, and there can be more minerals in the water due to run-off, or more chlorine in the water as they "shock" the system).  I didn't have time to think too much about it, so I stuck that one in to the fridge labelled "issue", and started again with 10g from a branch-off from the main rye starter that I'd stuck in to the fridge as "insurance" back in early March.  

Well - there wasn't a lot of joy happening with this one, either.  I ended up bringing it with me, and discarding and repeating the second feed a total of 3 times through the day (putting all of the discards in the "issue" container).  It finally seemed to show some movement right before bed, so I gave it a good stir and left it overnight.

Next morning, it hadn't quite doubled, but had shown some action, so I discarded the last feed again, and went for one more try.  I also started another one with 10g from my durum version of NMNF, and fed it with freshly ground hard red wheat (to see if it was the water).

The wheat one exploded happily in to life and doubled after the second feed, so I gave it the third feed and put it in to the fridge after it doubled again.  The rye one didn't double, but did grow about 40%, so I discarded one last time and tried again (added it to the "issue" jar), and then it did just double in the next four hours.  I gave it the third feed just before bed-time, and it was doubled and ready to go in the morning.

I now had two levains (had only planned on one), but figured that it would be nice to have a 100% whole wheat loaf using the wheat levain, and to do my husband's favourite rye banana loaf with the rye levain.  I knew that I wouldn't have a whole lot of solid time to spend on things, so figured that this would also be a good opportunity to see what would happen by following a method from one of Alfanso's bakes to use the fridge during bulk ferment to slow things down and make shaping easier, and still to do a retarded proof after shaping.

I wanted to keep things fairly simple, and also wanted to clean out some odds and ends of grains that were hanging out in the pantry, so my 100% fresh milled whole grain wheat loaf came out as:

39.3% soft white wheat
20% red fife
14% durum
13.3% hard red
13.3% spelt
79% hydration

It didn't come out as a "brick" by any means, had a reasonable oven spring, got close to the dark bake that I like, and did have the light but full crumb that I want in a "sandwich" loaf:


I had found that the loaves from the last bake had seemed to taste more dry than I liked, so I baked this one covered at 450 for 25 minutes, then uncovered at 425 for a further 30 minutes, only until it hit 203 degrees inside.  That solved my issue of "too dry tasting".

My rye banana loaf was our now "standard" of:

40% rye
60% AP
47% bananas
6.7% toasted oat bran / wheat germ porridge
6.7% toasted almonds
81% hydration (includes water content of bananas)

I didn't get a chance to start this one until later in the day than the WW one.  It didn't "feel right" to me during the stretch-and-folds, so I didn't chill it during bulk ferment, but kept it at room temp until it had risen about 30%, then shaped it and got it in to the fridge for a retarded proof.

It still wasn't feeling "right" to me the next day (I just couldn't get a feel for if it was under or over or proofing at all), but it came out of the oven okay:

It seemed to rise and open up fine, and the crumb and flavour were just what I wanted, so the "not feeling right" must have been from my worry about whether the recalcitrant starter was actually going to work or not.

All went well, and I had a couple of fine loaves to keep us in sandwiches for our busy days out and about...

Except - well, "issues" and "those days" continued in next blog...

alfanso's picture

But since it is "Italian bread", let's go with sesame semolina corona.  This is the Jeffrey Hamelman semolina dough with my 125% hydration rye liquid levain in lieu of his 125% bread flour liquid levain.

Neighbors due Friday afternoon for homemade torta di riso, rice cake - courtesy of my better half, home "brewed" limoncello, cheese -courtesy of various cloven-hooved beasts, and bread.  As I've made them my sesame semolina baguettes before, I decided on tackling a new shape, and have a preliminary run-through before subjecting any guests to it without a test bake.

Without a specialty banneton of any kind, it was time for some simple improvisation.  Using a 2 part Angel Food pan, I took the entire dough, already bulk risen and retarded, opened a hole in the center and dropped it into the pan.  Then back to retard it went for an overnight nap.  With a teflon-coated pan, there was no issue with the dough releasing cleanly.  A healthy swipe across the surface of the dough with a wet paper towel allowed the sesame seeds to adhere nicely.

15 minutes under steam, another 15 minutes after rotating and a final 2 minutes venting.  I've never baked anything greater than 750g , and then perhaps only twice, so this was a new adventure for me in a few ways.  Still too fresh out of the oven to cut open.  If all goes as planned, I'll prep the real thing today for a Friday afternoon bake and better form a round hole in the center.

Crumb shot added

1250g x 1 corona

Lazy Loafer's picture
Lazy Loafer

Many of you will be familiar with different versions of Peter Reinhart's Struan, a multigrain sandwich bread that he seems to have a version of in each of his books. I have often made the version from "Artisan Breads Every Day" and my customers (and I!) find it very tasty. I make it quite a bit.

I decided to try a version with some different ingredients, just for a different flavour profile, and I think I've hit on a winner. The original had corn meal, oats, wheat bran and cooked brown rice (I used basmati rice). This time, I substituted durum semolina, spelt flakes, ground flax seed and cooked wild rice. Here's the formula:

  • 351 g bread flour (I use Roger's Silver Star)
  • 23 grams durum semolina (fine)
  • 16 grams spelt flakes
  • 12 grams ground flax seed
  • 31 grams cooked wild rice
  • 31 grams brown sugar
  • 10 grams salt
  • 10 grams yeast (active dry)
  • 16 grams honey
  • 187 grams water
  • 62 grams kefir (could use any milk, or milk and yogurt blend)

All ingredients were mixed in a stand mixer for 2 minutes, then rested for 10, then mixed for another 2 minutes. The dough was stretched and folded at 10 minute intervals 4 times then bulk fermented in the fridge overnight.

Lovely stretchy soft dough...

By morning it had risen to fill the little container I put it in, and the dough was full of nice bubbles.

In the morning I shaped it and let it proof until an inch above the rim of the pan. I scored it down the centre (I do this for most of my pan breads so they don't split at the side) and baked at 350F for 40 minutes, rotating the pan halfway through baking.

It had nice oven spring and a good colour when baked.

I could hardly wait to cut into it, see the crumb and taste it - it smelled sooooo good! Also, I had orders for seven loaves and had to make sure it was good before making the dough for that order. :) And I was not disappointed...

The crumb is very moist and soft (mind you, I didn't wait until it was fully cool before cutting it, but still...), and a beautiful soft warm yellow hue from the semolina. The crust is thin and easily cut. There is enough texture from the slightly undercooked wild rice and the spelt flakes and the flavour is simply wonderful. I could eat half a loaf just with butter! Tomorrow I'll have a couple of slices toasted for breakfast (that's my second test). And bake another seven loaves!

Skibum's picture

Greetings friends, I haven't been posting much lately, as I haven't been baking much.

Super happy with my FoodSaver for storing fresh food and particularly bread. I baked a batch of soft pull apart dinner rolls April 26th. By vacuum sealing, freezing and taken out as needed. My last roll is as fresh today, 3 weeks later as it was when fresh from the oven! Take out a roll, re-vacuum and re-seal, then back in the fridge.

As a single ski bum I have either had to give bread away or double bag it in zip locks to freeze which never gave me a good re-heated product.

The vac sealer has also transformed my re-heating of my slow smoke BBQ. Pulled pork and vac sealer then re-heated sous vide style is as good a fresh pulled. My latest kitchen toy is a Anova sous vide precision cooker. Most impressed with the results so far!

Happy cooking, baking and eating folks! Ski

dabrownman's picture

My future SIL had a bachelor party in SF over the weekend and he was kind enough bring me a boule f the closest thing that Acme makes to traditional SFSD.  It was a bit more than day old by the time I got it.  Here is the website - they just call it Sourdough -

It is a handsome loaf for sure.  Deeply browned, scored perfectly with some blistering.  I give it a 10 on looks alone.  The crumb is moderately open for a bread that is all wheat grain - white flour.  I give it an 8.5 on the crumb.

It is slightly sour as today's SFSD breads seem to be and it is a a total white flour bread made of wheat so the taste is pretty bland.  I would prefer one with a bit of rye and spelt in it - say 5% each and one with a bit more tang to it so I give it a 7.5 for taste.

Overall it gets a 8.67 out if 10 - one fine bread for a balery that makes a lot of it.  Now I have t make some cioppino to see how it sops up a fine fish stew.


Doc.Dough's picture

This post has no pictures and is not going to interest a lot of readers since I did it to help my own understanding of what is going on in the oven.  Writing it down forced me to explain more when I didn't understand why and fix apparent inconsistencies.  If it is too much technobabble, just jump out and find something interesting. For those who wade through it, I welcome comments, corrections, clarifications, and questions.  Just consider it a work in progress.  When you understand this, you should be able to write the versions that apply to wood-burning ovens and deck ovens with external steam generators.


The modes of heat transfer from oven to bread include:

  • Conduction (by direct contact with a hot surface)
  • Convection (both natural and forced mechanisms from hot oven air)
  • Radiation (the heat flow between the oven walls and the bread in the oven)
  • Phase change (the evaporation of water from, and condensation of steam onto the dough surface)

For pan bread, the sides and bottom of the loaf are cooked by conduction of heat through the pan while the top is cooked by a combination of radiation, convection, and possibly condensing steam. The relative contribution from each mode is dependent on the oven, the temperatures involved, and whether there is any mechanical stirring of the air to enhance the convective heat transfer.

For freeform loaves baked on a metal pan, the bottom is cooked by conduction of heat through the pan while the remainder of the loaf is baked by other mechanisms.  When the baking surface is tile or stone or firebrick (something other than a thin sheet of typically aluminum or steel), heat stored in the baking surface is transferred by conduction to the loaf which both heats the loaf and cools the baking surface. The rate of heat delivery to the loaf is determined by the mass of the cooking surface, the initial temperature of the material, the thermal conductivity of the cooking surface, and the specific heat (cp) of the cooking surface material as well as the density, thermal conductivity and cp of the dough. The rate at which the energy stored in the baking surface is replaced from the oven primary energy source depends on the geometry, surface temperatures and convective flows, and also on what else is simultaneously in the oven (e.g., other loaves of bread or other pans above or below).

There is always some amount of free convection in any oven, driven by the temperature distribution within the oven which heats or cools air causing it to expand and rise, or contract and fall as its density changes. This results in the top of an oven generally being hotter than the lower shelf positions. Convection ovens have mechanical fans that circulate air within the oven to both increase the heat transfer rate to the food and to achieve a more uniform temperature distribution within the oven (top to bottom, side to side, and front to back). Even the small fans in widely available home ovens deliver very high temperature uniformity and shorten baking times because they increase the heat transfer rate from the oven heat source to the food.  The general guidance for using a convection oven is to reduce the temperature by 25°F and bake for the amount of time that is called for if you were using a conventional oven.

For most non-convection, non-steam injected ovens, radiation from the oven walls is the principle heat transfer mechanism.  The Stefan-Boltzmann law governs radiation energy transfer between the oven surfaces and the bread.  It takes the form of:

Qdot12= s A1 F12(T1^4 – T2^4)

where s is the Stefan-Boltzmann constant, A1 is an increment of oven wall area, F12 is a shape factor that accounts for geometry and surface emissivity, T1 is oven wall temperature and T2 is the bread temperature (both in °K).  Note that the heat transfer rate Qdot is proportional to the difference between the fourth powers of the absolute temperatures.  This is not (T1 - T2)^4, but T1^4 - T2^4 which is a really big number at typical bread baking conditions [T1 might be 250°C (523°K) and T2 might be 15°C (288°K) at oven entry].   At these temperatures, a 30°C reduction in oven wall temperature produces about a 20% reduction in radiant heat transfer rate and about a 13% reduction in convective heat transfer rate.

In steam-injected ovens, condensation of water on the surface of the dough delivers a lot of heat.  The enthalpy of vaporization for water (2250 J/g), is more than five times the energy required to heat the same quantity of water from 0°C to 100°C (418 J/g) and is delivered directly to the surface of the dough when steam condenses. Steam does two things for you; it brings water directly to the dough which helps to fully gelatinize the starch forming a shiny, waterproof, gas tight membrane that prevents CO2 from escaping through the surface (thus forcing dissolved CO2 in the dough just under the skin to form blisters when it comes out of solution as the dough temperature rises to exceed the temperature at which the CO2 can remain dissolved).  The cooked surface is also physically strong and cannot stretch to accommodate expansion of the trapped CO2 (oven spring) and will thus facilitate fracture along the lines defined by your lame when you slashed the dough (or randomly at weak spots if you forgot, or slashed ineffectively).

During the first few minutes in the oven, the dough is cool enough to condense steam on the surface, and the more steam there is in the oven the more effectively and rapidly it cooks what will become the crust.  If there is inadequate steam, the dough will still cook, but the starch will not be fully gelatinized so that the crust is not as shiny or gas tight as you might desire and the coloration will be different and generally dull.

When the surface temperature of the dough gets high enough that it exceeds the local water vapor saturation temperature (oven dew point) steam no longer condenses on the crust.  At this point, while the specific heat (cp) of unsaturated steam is somewhat higher than dry air (by about 2x), the dominant heat transfer mechanism in a non-convection oven switches over from phase change (condensing steam) to radiation (from the oven surfaces). In convection ovens, the size of the fan and the capacity of the heating elements will determine whether radiation or convection will be dominant. In most home ovens, the convection fan is adequate to maintain uniform temperature throughout and does increase heat transfer by about 15% above what it would be with radiation plus free convection, but does not provide sufficient air velocity to raise convective heat transfer to a point where convection dominates radiation as the mechanism for transferring heat to the bread.  In commercial convection or combination ovens, the situation is reversed and since the heating elements and the convection fan are big and powerful, they transfer heat via convection considerably faster than radiation alone.

Gas ovens (with burners that share the bread baking volume) suffer from the absolute need to exhaust combustion gasses when the fire is on and in the process sweep out both the steam that is generated by combustion and any steam that is added to the oven (by both your steam generator and by evaporation from the bread dough itself).  The conventional solution is to preheat the oven to very high temperature, include some additional heat storage capacity in the oven (tile, brick, stone, scrap iron), then turn off the gas and plug the vents after loading the bread until there is no additional value from further steam. At this point you can unplug the vents, re-ignite the flame, and remove your steam generator from the oven.

Crust thickness is determined by the depth to which the baking bread has been depleted of moisture, and is generally a function of both oven temperature and oven cycle time. If the oven is too hot, the bread will over-brown before it develops a thick crust.  If the oven is too cool, the crust will be light in color even though it may be relatively thick.

When generating steam by boiling water inside the oven, some energy that would otherwise go toward raising the oven temperature is used to boil water.  This can be a major factor in small ovens and is important to understand.

Bread loses about 15% of its initial weight to evaporation of water during the bake cycle, thus a 750g loaf will lose ~110g of water.  It takes 2.13 BTU/gm to evaporate the water so you expend about 235 BTU in the process. That 235 BTU is about 68 watt-hours of energy, which you can allocate over the bake cycle and think of as reducing the effective power of the oven.  For a 30 min bake cycle that is like reducing the 2500W heating element by 136w to 2364W except that the effective reduction is bigger at the beginning of the cycle than at the end because there is more water to easily evaporate at oven entry. 

If you consume a pint (pound) of water in a steam generator, you will use 1000 BTU or 0.3 KWH to convert it to steam (plus 1 BTU for every °F that the initial average water temperature is below 212°F).  A 2500W oven will take about 7 minutes to recover the heat lost to the steam generator, and for a 4.5 cu ft oven, it takes about 75g of water to produce enough steam to fill the oven.  You will have to make an assumption about how tight your oven is but it would not be a bad assumption to guess that you lose one oven volume of steam per minute of active steaming. My observation is that after the first five minutes in the oven, the surface of the dough stops looking wet, and for rolls and small diameter loaves, they have completed almost all of their oven spring (note that there is an alternate view that says you should steam until the dough begins to brown – just figure out what works for you).

Seventy five grams of water takes 3.84 KW-minutes to boil, but you need 75g of steam per minute (about a pint for five minutes of steam if you leak at one oven volume per minute), so with a 2.5KW oven, if you don’t want to substantially cool off your oven in the process of making steam, you need some energy storage in the oven.  Lava rock has a cp of around 0.2 so it takes a bit more than a pound of lava rock at 400°F to generate 5 minutes of steam, but that is not unreasonable since you will heat the rock up during your normal pre-heat cycle (I am assuming it takes 1 hr @ 500°F to get the lava rock thermally charged to 400°F in a non-convection oven). And you will want to use boiling water to charge the steam generator so that you don’t use another 20% of additional energy to heat the water up to boiling.


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