The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

"Magic Bowl" effect with an aluminum foil roasting pan

dmsnyder's picture

"Magic Bowl" effect with an aluminum foil roasting pan

Covering loaves during the first third to half of the bake is one way of achieving a humid environment in a home oven, Its purpose is to approximate the effects achieved by injecting steam into commercial ovens. It enhances oven spring and the spreading of cuts (bloom) in the loaves. This technique has been discussed extensively and repeatedly on TFL.

Various members have used pyrex bowls (with the risk of shattering), stainless steel bowls, larger roaster covers and ceramic covers such as "La Cloche." Each has its advantages and limitations. Most bakers want to have covers for both boules and long loaves such as baguettes and bâtards. Oven size and baking stone size present limitations to the feasible options.

After having had success baking boules under a stainless steel bowl, I wanted to use a cover for baking long loaves. I used the cover and the base from a large enameled steel roaster a couple of times. Its length was just right for my baking stone, but it was a bit too narrow to comfortably accommodate two bâtards. I had loaves stick to the sides of the roaster a couple of times, damaging the crust. Looking for alternatives, I found a couple of large, light-weight aluminum roasting pans in my pantry. They are 15.75"x11.25"x3". My stone is 16"x22", so they fit on the stone well.

They don't have quite as good a seal with the surface of the stone as more precisely made alternatives, but the results of using them is pretty close to that achieved with other covers. On the positive side: They are meant to be disposable (although I use them over and over again), and they are very inexpensive. Also, they come in a wide variety of sizes and shapes.

The brand I have is called "EZ-Foil." Here is a link to the company's web site:

The online vendors I found only sell these in large quantities. I got mine at a local hardware and housewares store in a package of two pans for something like $5.00. Maybe less.

I have no financial connection with this company and am not saying it's "the best." It's just the one I happen to have bought. 


niagaragirl's picture

It's a great idea for those who want to simply give the method a try without a big financial investment to see if there's improvement. And they can be found in most supermarkets, and even in the dollar stores these days.  Although the dollar stores may carry a different brand.

Jw's picture

thank you David, for that great tip. That kind of material is available around here as well. Would you still use other methods for humidity? Cheers, Jw.

dmsnyder's picture

Hi, Jw.

I still use a SS bowl for boules. For longer loaves, I most often use Hamelman's method - pre-humidifying the oven before loading with ice cubes in a metal loaf pan and steaming after loading with boiling water in a cast iron skillet.


xaipete's picture

Well I guess this post is that last word on foil pan cloches! Thanks for gathering all of this information together, sharing your experience, and putting it in one post.


Susan's picture

I've been thinking about the three ways an oven cooks.  A stainless steel (SS) bowl stops convection and radiation from the oven, and only bakes by conduction (at least until the SS starts radiating its own heat).  A Pyrex bowl allows both radiation and conduction from the oven.  Conduction between the SS bowl and the Pyrex would be different, I think.  Is the Pyrex bowl--because of its mass--keeping the crust cooler longer, allowing for a longer rise?  Think of the punch of heat from below, too!  These factors are complex, according to my ChemE husband, who offers this info.

Even though I use an SS bowl here in Prescott, and occasionally use a big rectangular roaster in San Diego, my favorite is still the 4L Pyrex bowl.  (As an aside, I am not seeing any changes in my bread because of the altitude difference--350 ft in SD to 5,750 ft. in Prescott.)

Admittedly, Pyrex is much more dangerous.  I've not had one shatter, though I did hit the edge of one against the edge of the granite counter and chipped it big-time.  That one immediately went in the trash.  The major problem with the Pyrex bowl, as I see it, is that it is terribly hot, heavy, and hard to handle when removing from the oven.  An oven mitt or pocketed hot pad or Ove' Glove does the trick, but I hate to think about a burn from the hot glass. 

It's quite possible that the reason I like the Pyrex so much is that you can SEE the loaf rising, and that's so much fun!

What does the Peanut Gallery have to say?

Susan from San Diego


xaipete's picture

I seem to recall reading something about the nature of pyrex and shattering. I've had an occasional pyrex shatter in my lifetime and well calling it a shatter didn't do justice to the incredible mess and number of fragments.

At any rater, pyrex is more prone to shattering, I think, when it is cooling down. So, if that is the case, where you put the bowl after it comes out of the oven is probably pretty important.

I noticed that there are some very expensive oblong glass roasters on eBay, just incase anyone is interested.


xaipete's picture

I found the article I read about pyrex on Cook's Illustrated. --Pamela

Published November 1, 1998.


When do I risk having a baking dish explode? Can I put a frozen glass pie plate directly from the freezer into the oven?

The problem of exploding glassware is not unfamiliar to us. An editor here had a Pyrex dish containing roux (a mixture of fat and flour) shatter on him after removing it hot from a microwave to a cool, damp countertop. To find out what might have happened in your case and his, we contacted Don Miller, an engineer who supervises the glass lab at the University of California at Santa Cruz.

IMiller offered several possible explanations for our exploding glass. One is that the glass may have been scratched, which, he said, "can happen by many means over years of use. Once this happens, it changes the whole structure of the glass and makes it more vulnerable to breakage." Another is temperature change. "The fact that it broke in many pieces," he said, "leads me to think there was a reaction with . . . a cold surface." Yet another possibility is moisture. If it comes into contact with moisture of any kind, this alone could make the hot glass break. Combine any two or all three of these factors, and you have a recipe for disaster.

We checked out these theories with Jim Kamandulis, senior quality analyst for World Kitchen, the company that owns Pyrex. He concurred on all counts, even giving us a name for such events: down-shock. 

Down-shock occurs when there is a sudden cooling of a glass surface. If any flaws, such as scratches, are present when such rapid cooling occurs, the dish can shatter. The opposite, up-shock (breakage upon a sudden heating of the glass) can also occur, he said, but glass is much more vulnerable to down-shock. 

How to prevent down-shock? Miller suggested inspecting the dish before use by turning the bottom toward your face and then looking into bright light, but often it's impossible to detect a tiny but fatal flaw. It is possible, however, to avoid the problem of contact with a hard, cold, and/or wet surface by placing the hot dish on a clean, dry dish towel. Kamandulis also advises strongly against using even slightly damp potholders to remove a hot Pyrex dish from the oven; they, too, can cause the dish to break, right in your hands. 

Moving Pyrex From the Freezer to the Oven It should be fine to transfer a filled Pyrex pie plate from the freezer into a preheated 425-degree oven. However, Kamandulis emphasized the need to preheat the oven before putting the pie plate in. He explained that the pie plate would likely break if it came into contact with any direct heat source and also that some ovens may use the broiler as well as the bottom heating element to quickly heat up to the desired temperature, resulting in a heat intense enough to be regarded by Corning as the equivalent of direct heat.

The transfer from freezer to preheated oven is okay because the glass from which Pyrex products are made is tempered. Tempering, Kamandulis pointed out, is a mechanical strengthening process that increases the thermal shock resistance of the glass. The glass is heated to a uniform temperature and then quickly quenched with air, a process which amounts to rapid chilling. This creates compressive layers on the surface of the glass, increasing its impact- and thermal-resistance.


LindyD's picture

As much fun as it would be to watch the action in the oven, Susan, my relatively new stove carries the scars from removing a cold stone from the oven.  I wouldn't attempt Pryex even if I had TWO Ove-Gloves.  Murphy's Law thrives in my kitchen.

The stainless steel bowl has worked well - I haven't yet tried my jury-rigged foil cover, but will get a chance to do that in a couple of hours when the Pane Francese rolls are loaded.  If it works okay, tomorrow I'll use it on the Pain à l'ancienne my kids requested. 

9:52 p.m edit:  I've no idea whether the foil cover worked or not.  I baked nine rolls covered and nine rolls with normal steam.  They took the same amount of time to bake and looked the same coming out of the oven.  Round two, tomorrow...

merrybaker's picture

There's more Pyrex exploding out there than you might think --

SylviaH's picture

Many years ago I had a large pyrex baking dish...crack in half in the oven..messy and had do apparent damage going in...I don't know what I did wrong!  I still use them...carefully and for lower temperature cooking and baking.


xaipete's picture

All these products are capable of shattering, and I think I had a least one piece of each of them shatter in my life time.


SulaBlue's picture

With Le Creuset stoneware?

xaipete's picture

Hi Susan. I've been thinking about your post and what you say about the various differences between types of covers and heat conduction. Why I don't doubt what you say is true, I wonder if it is really a factor when the loaf is only being covered for the first 10 to 15 minutes?

An aside: I bet a pair of the silicone gloves would be a great at lifting off the hot pyrex bowl.


Janknitz's picture

What an interesting discussion on the transfer of heat through various materials!

I have had amazing success with a foil pan and with a clay cloche.  I've only used it once so far, but by far the best results have been with the clay cloche.  

For highly hydrated doughs (i.e. AB in 5 or no knead), it is not necessary to spray the bread or wet the cover--there's plenty of hydration in the dough that seems to vaporize and provide adequate steam.  

mountaindog's picture

Thanks David - do you find that 3" deep is enough for your batards and boules? I'll give it another shot. I have a very large stone and like to do multiple loaves and boules, so I've been thinking of getting a hotel pan/steam pan from a catering supply house, but still not sure if I can find one big enough for multiple loaves.

dmsnyder's picture

Hi, md.

I've never had a problem with 3" being insufficient. The only issue has been with the width being adequate to accommodate two loaves far enough apart to brown evenly.


samf526's picture

Has anyone had their baguettes rise/spring in very unusual, deformed shapes when covered by an aluminum roasting pan?  I've been trying this method for a few weeks now, and invariably, my baguettes do not expand uniformly along their lengths or along their widths (think of a hilly terrain).  They also end up somewhat flat (similar to what people have described when they oversteam....which has never happened to me, as I have a gas oven that doesn't ever retain enough steam).  However, I usually cover the baguettes only for ~6-7 minutes, so oversteaming seems unlikely.

Re: the nonuniform expansion in the oven, could this be due to a lack of proper heat circulation under the aluminum pan?