November 26, 2007 - 7:31am
Better heat transfer
I am having problems with even heat in my oven. The loaves baked on the top rack pop up just fine, but the loaves on the lower rack tend to spread out a bit rather than springing upward. The difference is easily noticeable. I use stones, but I'm thinking that's not enough. I've been looking at the HearthKit, and Fibrament stones, and also at someone's homemade HearthKit (tiles lining the oven walls in addition to baking stones). I've also thought about convection, but to get even heat, I'm thinking I'd have to turn on the convection at the beginning of the bake, thus minimizing oven spring. Does anyone have a method that works better for them? Has anybody compared the Fibrament and the HearthKit?
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It's a common problem with conventional style ovens. You just can't get even heat especially with cooking on two racks. Maybe you should just try to time it so that one batch of bread cooks at a time. Professional ovens use revolving racks or individually heated decks. you can't simulate this in a home oven. Lining the oven walls might work some as you'd have some retained heat. I use a stone but none of the items you mentioned.
I have a convection/conduction oven and from my experience the convection isn't really worth getting. It isn't a real convection oven anyway (as I understand it most residential ovens that say they are convection are the same). There is just a fan in the back that circulates the heat but the heating element in the bottom of the oven still provides all the heat. A real convection oven heats the air and blows that hot air into the baking chamber. Anyway, I bake all my bread on the normal oven setting. I have never had luch baking more than one layer at a time. You might look at how much of the oven rack is covered by your baking stones. You need a couple or three inches of clear space on all sides to get good heat circulation. I'm surprised that the bottom loaves are the ones that are having problems as they are the ones that are receiving the most heat both from the heating element and from the retained heat of the stone. I think your best bet it to time your loaves so you can bake in one layer. I've read of routines where people mix up dough for 6 or 8 loaves and then retard the dough to different levels in the fridge so when one set of loaves comes out the next set is ready to go in. I'm not that good nor am I that organized so I bake one layer at a time, one batch each time. You know, the easiest solution if you have the space (and money) is to just buy a second oven or double wall ovens.
I hadn't ever heard that about convection ovens--it's good to know. The difficulty I'm having is that I really do need to bake using both racks. I have 2 sets of double ovens (so 4 ovens total) that I use in my home operation. For several reasons I won't go into here, a commercial oven isn't an option, at least not right now, and so I'm stuck with what I've got. I have baked bread just starting loaves on the top rack, and when it comes time to move them to the bottom, then another set goes in on the top, but that's really time-consuming. I don't understand either why the bottom rack is the problem; it would make more sense for the top to be. I suppose I just need to play around for a while and see if I can come up with a better solution.
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How tall is your oven, and does it have 3, 4, or 5 rack positions? One thing that occurs to me is that you just need more stored heat distributed more evenly. You could put an extra thick layer of stone on the bottom shelf and another stone on the top, increasing both the thermal mass and the radiant heat from the top (you might need to buy another shelf though).
If there isn't enough room for that, you could try putting a stack of refractory bricks on the sides of the shelves in use, again with the idea to simulate a brick oven and increase the overall thermal mass.
Just some random thoughts.
sPh
I had those same random thoughts. I'm not sure exactly how to work these things (your ideas are good) but my dad, who is much stronger in science than I am, wants to help me out. I'll have him read your comment.
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If you use two shelves, each with a stone, and preheat your oven correctly (minimum one hour) both stones should hold a large heat capacity. Oven spring requires a well heated stone, a loaf that is not overproofed, and steam.
Correct pre-heating pretty much rules out the heat factor. I know that heat in the oven might be uneven, but I think that would mostly manifest itself in differences in browning, baking time etc., but not too much in oven spring. Remember that the yeast dies when internal temp reaches around 140F (I believe). Even in an uneven heat situation your breads would reach this temperature at similar times because of the stones (they are the same aren't they?). The exception would be if your stone(s) do not leave enough room on the sides for correct air/heat circulation throughout the whole oven. You need at least 2 inches on either side. Now, if you do not heave sufficient steam, and what you have rises to the top with the other hot air, the bottom shelves would suffer steam deprivation. The crust will form too quickly and upward spring becomes hard/impossible. In addition, the bottom shelf is under additional heat stress because there is a stone both below and above this bread. The top shelf only has a stone below. This may exacerbate the crust drying out too quickly.
Although I can't come up with a reasoning about the effect of a nearly over proofed loaf right now, I imagine that if your loaves are nearly overproofed, the differences in environment that I describe above, could push the bottom loaves over the edge and cause some collapse (which would show as flattening, but should also be visible in the crumb structure).
You can't really use convection setting if you are also using steam because the fan would accelerate evacuation of the steam through the oven's vents. If you do not use steam, then I would definitely try the convection setting for a temperature lowered by 25F. What I would do is some experiments, carefully controlled. Observation of the results should point you in the right direction.
--dolf
See my My Bread Adventures in pictures
I was thinking about all these other suggestions above and all have good validity. what did strike me though is that you are having trouble with the bottom loaves and not the top. It's usually the other way around. You also say the bottom loaves flatten out. That sounds like overproofing, but it should get the same results for the top. Maybe it something you are doing. Let's say both sets of loaves are slightly overproofed. for some reason or other you are able to get the top loaves in more gingerly then the bottom. Then you go to the bottom loaves and kind of kerplunk them on the stones. this would cause them to flatten. maybe the lower rack is harder to get at because you can't get in at the correct angle. you're tall or don't or can't bend down enough or something. Maybe try to proof a little less than you are and try to get the bottom loaves in first and work at a better slide angle. Steam would effect over all oven spring, but I don't think it would cause them to flatten, More oven mass would be better retained heat, but not necesarily heat distribution. Mass on the oven walls could seriously effect circulation. Maybe it's just your technique. Over all a simpler and cheaper fix. Plus less proofing takes less time.
I have experimented with over and underproofing, in addition to it (hopefully) being just right. The loaves in the bottom tend to tear and bulge with over, under and correct proofing. The problem is lessened with overproofing, but then it's even flatter than it would have otherwise been. I am very careful when I slide my loaves into the oven, so I don't think that's the problem. My stones don't cover the whole rack, not by far. I preheat my ovens for at least an hour; the loaves that are baked at the end of the day (when the stones have been heating for several hours) have the same problem as the loaves at the beginning. I've experimented with several steaming techniques, but I haven't found any that really made a difference as the steam quickly comes out of the oven vents. I haven't really experimented with Susan's magic bowl, though. I'm afraid of burning myself, which is something I am prone to doing. Both my sets of ovens are the same model; maybe I should ask a neighbor if I can make use of their ovens to rule out the idea of just having a bad set of ovens for bread baking.
SOL
I use the top and bottom racks in my home oven with no problem, so the situation can be addressed.
It is important to understand that home ovens are uneven. Most professional ovens are uneven as well . As a result, half way through baking, I pull the bread out, switching between top and bottom shelves, and turning the bread so what faced forward now faces back.
I put tiles on both racks in my oven. I had to play with that a bit, because it seemed to make the uneveness worse. I settled on having about a 2" space on the left and right sides of the lower rack that is not covered. And a 1" space on the top rack. That allows enough air movement to let things stay fairly even.
Tearing around the bottom of the loaf is usually indiciative of low dough strength, poor loaf forming techniques, or not slashing the loaves.
I would work on dough development, perhaps making a somewhat dryer dough as well. Look into how you are forming your loaves. Weaker doughs need more force in loaf formation, stronger doughs you can be more gentle with. (Assuming you aren't playing with super liquid doughs like ciabatta... that's a different ball game.)
When you get oven spring, and it isn't entirely clear that this is an oven spring issue, slashing the loaf controls where the spring will occur. Oven spring's loaf tears will occur at the weak spot of the dough. When you slash the dough, you are creating a weak spot, and that is where the dough will expand the most.
Hope that helps,
Mike
My digital camera is out of commission right now, else I would take a picture of the 15 loaves each of Potato Rosemary Sourdough (boules) and the Blue Cheese and Walnut Sourdoughs (batards) that I started on the top racks today. All of them are beautiful loaves, no tearing, not flat. My doughs tend to err on the too strong side, rather than being too weak (as soon as I've used up these last couple of bags of flour, I'm switching brands, but that's another ball of wax). I use a gentler touch when shaping a dough that's a bit too strong. In my experience, it's the stronger doughs that have a greater tendency to tear, not the weaker ones. All of my loaves are scored symetrically in such a way that (at least on the top shelf) the ovenspring is even. If it were a problem with my technique, then I shouldn't be able to get good loaves on either rack, but like I've said, the loaves started on the top are fine. I have noticed that although still a problem, it's lessened in the few loaves I make that aren't sourdoughs. I think I'll test by removing the stones and bake a couple loaves on baking sheets to see if my stones' location is wreaking havoc on the heat distribution.
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Do you ever see things without actually seeing them? I opened the oven the other day to load the bread when I saw that my stones did cover up practically the whole rack for both the top and bottom. There was a little room front to back but practically none side to side. Why I thought I left enough room is beyond me. I experimented a bit yesterday and discovered that if I leave a little room open on each rack for air circulation, I end up with perfectly shaped loaves, top and bottom. Problem solved.
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