The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Cure for Burnt Bottoms?

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chris319's picture
chris319

Cure for Burnt Bottoms?

I hope I have found the cure for burnt bottoms on my sourdough boules.

I found a table of the heat conductivities of various materials. I had been using metal vessels to bake, and the bottoms of things kept getting burnt in my electric oven.

Not surprisingly, glass is a worse conductor of heat than metal. Air is an even worse conductor. This suggested a remarkably simple solution.

I took two 9" Pyrex pie plates and nested/stacked them. Once stacked, there is an air gap of 1/8" to 1/4" between the two pie plates. This air gap acts as an insulator. To prevent sticking, I sprayed the bottom of the top pan with cooking spray. I then baked some Pillsbury canned biscuits just to test the efficacy of my solution. It worked! No burnt bottoms! Parts of the biscuits were just a little darker on the bottom, but they were nice and golden, not burnt. I think I'm onto something.

A little about my baking setup: I'm using a modified Waring TCO600 6-slice toaster oven and I like it a lot. I modified it by removing the upper heating elements. These caused the tops of things to burn so out they came. Now it just has the lower elements like a full-size oven's bake element. I use a toaster oven because it seems wasteful to use a high-wattage full-size oven for something as small as a boule or six biscuits which use just a fraction of a big oven's interior volume. The toaster oven has a much smaller interior and with my modification draws only 750 watts when the heating elements are on. I had been using a metal "heat shield", the toaster oven's metal baking pan, over the heating elements, much like a gas oven,  but found this to be energy inefficient. The insulator only needs to be under the food, not over the heating elements. I had been using a "baking stone" made of Teflon and it worked quite well indeed, but opted for a non-Teflon solution due to (possibly unfounded) health concerns about the toxicity of Teflon. I have ordered a small silicone rubber cake pan to be placed inside the top pie plate as a sort of liner to prevent sticking and eliminate the need to use cooking spray.

Wood would make a great insulator but I don't think it could withstand the oven's 400 - 450 degree heat.

Next I have to adapt this solution to work with a muffin pan.

dabrownman's picture
dabrownman

electric oven uses 3000 watts per hour according to its spec sheet.  Assuming it runs full blast for an hour and half to preheat to 550F for an hour  and bake at 475 F for a half an hour that would be 4,500  watts.  At 10 cents a Kwhr,  I figure it costs 45 cents to bake a loaf of bread.where your mini oven, if it preheats and bakes a loaf of bread in an hour like mine does, it's only 7.5 cents - big savings percentage wise if not that much money wise. 

They make stones for the mini ovens too kind of expensive but I have seen them at Goodwill for a buck or two occasionally.

happy baking

Bakingmadtoo's picture
Bakingmadtoo

But does your oven run at full blast for all that time? Mine certainly doesn't, it gets up to temperature in about 15 mins, after that it uses hardly any electric, just coming on and off occasionally to maintain temperature. I have a smart metre, the first 15 minutes it runs at around 60p per hour, after that it drops to under 10p per hour, with the odd blast at the higher rate. So I have never really managed to calculate the cost of baking a loaf in mine.

dabrownman's picture
dabrownman

producing mega steam in ahout 20 minutes after that is runs part time but it is a 1,250 watt Cuisinart so i figure about 10 cents a loaf in it vs 3-4 times that amount in BOB but the Big Old GE doesn't run all time for a hour and a half either.  Wether it si 8 or 12 cents for a loaf of bread isn't critical since my apprentice comes from German  aristocracy - she can afford the 4 cent difference in a low or high guesstimate:-)

Bakingmadtoo's picture
Bakingmadtoo

Chris319, I am constantly amazed at the ingenuity of folks here. I think somewhere on this site there must be solutions for every problem a baker might come across!

lazybaker's picture
lazybaker

T-fal has a line of AirBake baking sheets that have air in between the aluminum sheets. I haven't tried them.

I use two jelly roll pans on top of each other. I think there's a small air space between them, too. I have to do this, or else my croissants come out burnt at the bottom if I use one jelly roll pan.

I wonder if you could just place a baking sheet under the muffin pan. Also, lighter pans don't retain heat as darker pans do. Still, over-browning occurs with light pans but not as badly as darker pans.

Mini Oven's picture
Mini Oven

Gosh, I hope mini oven owners are not taking their ovens apart, when all they had to do is turn down the temperature.  

Removing the top element because it burns the tops and then buffering the bottom of the loaf because the now exposed  lower coil burns bottoms because it now has to make up for the loss of top heat, seems backwards.  Your tinkering frankly leaves me scratching my head.  Why?  Can you explain or expound more?  Why not reduce the size of the loaves or get a bigger oven? 

Over browning and burning usually means the heat source is too hot or too close to the bread.   Did you try turning the heat down and bake inside a casserole?  It's a great solution for small ovens.  It protects the loaf, spreads the heat around the loaf and holds steam next to the crust for nice expansion.  

chris319's picture
chris319

all they had to do is turn down the temperature

If the solution were that simple why do you think I'd be going to all this trouble?

The crux of the problem is that the bottom cooks faster than the rest of the loaf/biscuit. When the top is golden brown the bottom is burnt black. Part of the reason is that the part of the loaf not in contact with the baking surface (with the upper heating element disabled) is heated by convection (hot air). The part that is in contact with the baking surface is heated by conduction (it is in contact with metal/glass/whatever). Remember convection and conduction from science class?

You can turn down the temperature but you'll have to bake longer. If you don't increase the baking time at the lower temperature your baked goods will be underdone. There is still the problem that the bottom is cooking faster than the rest of it.

the now exposed  lower coil

The lower element is always exposed. It comes from the factory that way.

A full-size electric oven has two heating elements: the "bake" element on the bottom and the "broil" element on the top. Go to your electric oven and turn it on as if to bake. Do you see the broil element coming on? No, you don't. There's  a reason for that. Toaster ovens are designed to make toast. For that reason both the top and bottom elements come on at the same time to toast both sides of a slice of bread. I disable the upper element to emulate a full-size electric or gas oven. Now there is a further complication: by leaving the upper heating element operational, the food is directly exposed to the radiant heat from the heating element and this is what burns the tops of things. The law of gravity dictates that the food sit on some kind of surface. This surface gets between the food and the lower heating element and acts as a heat shield, so there is no direct exposure to the radiant heat from the lower element.

 Why not reduce the size of the loaves or get a bigger oven?

A full-size oven uses a LOT more energy for two reasons: 1) the heating element draws more power (2400 watts vs. 750 watts) and 2) a full-size oven has a huge volume of unused space inside. All that space is fine if you're doing two thanksgiving turkeys for a family of 12 but for a boule or a pan of 6 biscuits it's cavernous. Reducing the size of the loaf won't help. Biscuit bottoms burn and they're pretty small. When I make biscuits with garbanzo or almond flour, burnt bottoms are a serious problem. Those flours are less forgiving than wheat flour.

Did you try turning the heat down and bake inside a casserole?

A glass casserole dish is going to act as an insulator, i.e. it's not going to conduct heat very well (remember my saying glass is a poor heat conductor?). Once again we're throwing away energy because the glass is keeping it out. The insulating properties of glass are why I use Pyrex under the food and by golly it works well! I have an iron Dutch oven which weighs a ton and is too big to fit inside a toaster oven.

I have some airbake sheets and they do work well -- but only in the big oven. They're too big to fit inside a toaster oven.