I have a confession to make: I love my little cob oven, but I really don't fire it up all that often. I bake bread and make pizza all the time (doing one or both at least once a week), but 9 times out of 10, I opt to cook them in my electric oven, even during the summer, and even despite the fact it tops off at a measly 550 degrees. And here's why: she's a beaut (or at least she was, until I cocked up the "decorative" plaster layer we added a few months ago, leaving her riddled with the unsightly, parched-desert-floor cracks you can see in the image above), but she's not very efficient. It takes a lot of wood and at least two hours of firing to get her hot enough to use, and even then, she's usually only got enough gas to handle one load of bread before cooling down. That's a lot of time, wood, and effort for 4 loaves of bread. Pizza fares a little better; once the oven is hot, she stays hot enough to keep making pies as long as there's a small live fire going at the back. I've dreamed about someday trading her (sorry, Dear) in for one of those luscious (and larger) Le Panyol ovens, like the one I used at the Kneading Conference in July, but, even if I could afford the 5-10 grand an oven like that would cost, it wouldn't really solve my problem.
That's because dome masonry ovens, regardless of size or which end of the cost spectrum they sit, are inefficient when used infrequently—as they are in most home settings—since they operate by virtue of retained rather than direct (or continuous) heat. Unlike my (or your) range oven, which comes up to temperature relatively quickly and stays there as long as you don't move the temperature dial, you have to burn a lot of wood before a retained heat oven is ready for use. Retained heat equals delayed heat. The heat of the fire first gets pumped into the mass of the oven walls and floors; only after the masonry is sufficiently saturated with heat does it begin to reverse direction and heat the oven's interior. The bigger the oven—or the thicker its walls—the longer the delay (which is why a fancy and roomy Le Panyol is no real panacea.)
Bread is baked in retained-heat oven without the presence of a live fire; after the oven is saturated, the fire is raked out and the bread loaded. At this point, the oven only stays up to temperature as long as there is enough heat socked away within the masonry. Each load of bread depletes the amount of heat remaining in the masonry; after so many loads—depending upon how long the oven was originally fired—the temperature within the oven will begin to plummet, requiring a second firing before more bread can be baked.
While pizzas and flatbreads are typically baked using a live fire, cooking them properly still calls for a fair amount of heat to be stored in the masonry, for two reasons. First of all, pizza cooks from the bottom and the top simultaneously. In order for the bottom of the pie to cook quickly, the floor of the oven needs to be hot (and to stay hot—just as with bread, unless there is a good reserve of heat buried in the hearth, each subsequent pie will draw down its temperature). Secondly, live-fire cooking calls for an already white-hot oven. Not only is the flow of air into the oven faster in a hot oven (ensuring a clean, bright fire), but the fire itself serves mainly to augment the heat supplied primarily by the surrounding masonry.
In a commercial setting, where an oven gets used day in day out, the inefficiencies of retained heat ovens disappear almost entirely, because the oven never sees enough time between firings to cool down. Each firing serves only to restore what little heat is lost during the down time (and in a well-insulated and tightly sealed oven, little heat need be lost). Daily firings of these ovens are akin to topping off a nearly-full gas tank every morning on the way to work: it doesn't take long, and there's zero chance of the needle ever getting close to E.
Until I have my fantasy bakery/slice joint up and running, where I can fire my oven daily, I'm left in something of a bind. Like most of us, I lead a busy life, and don't really have enough time to take full advantage of my WFO. And even if I did have the time, it's an awful waste of resources (even renewable ones) to burn all that wood for a few measly loaves of bread or an evening's worth of pies. I still use my cob oven, but not very often, and not without a twinge of guilt each time.
But I think I've found a solution to my dilemma. Enter the barrel oven:
I recently stumbled upon a website called Firespeaking, run by Oregon-based husband-and-wife cob and masonry builders Max and Eva Edleson. They have begun promoting the building of what are known as wood-fired barrel ovens as a modern, more efficient take on an earthen WFO. It was their description that first caught my attention:
The "barrel" oven is a very practical and wood-efficient oven which can be built at very low cost using mostly natural and recycled materials. The oven is sometimes also called a "mixed" oven because the heat generated by the wood burned cooks both by directly transferring heat into the cooking chamber as well as by retaining heat in the oven's mass and slowly returning that heat to the inside of the oven. For these reasons, this oven is much more practical to use and requires much less wood to do the same amount of baking as in the retained-heat mass ovens and traditional domed earthen ovens. It allows for quite a bit more spontaneity too since you can be baking just 15 minutes after lighting your fire. The firebox and the inside of the oven are sealed off from each other so the baking chamber is always clean of ash and carbon-black.
Here's the money quote, in case you missed it: "[The barrel oven] allows for quite a bit more spontaneity too since you can be baking just 15 minutes after lighting your fire." 15 minutes?! Holy cow! Not even a range oven gets hot that quickly.
Here's how it works: the fire is built in a long firebox toward the base of the oven, with its flue running up and around the exterior of a 55-gallon metal drum sitting above it, and then out the chimney. Dome ovens typically have limited airflow until the fire and oven is hot enough to create strong convection currents, which usually necessitates starting with a small fire near the door, only adding wood and moving it back toward the back of the oven as heat begins to build. By contrast, the fully vertical design of the barrel oven means that a healthy draft is established easily, ensuring efficient, complete—and clean—combustion of the wood almost from the get go. And because the barrel is made of (highly conductive) metal, it easily absorbs much of the heat produced. Meanwhile, because the barrel and its surrounding airspace are encased within masonry walls (made of clay, just like a cob oven), which have loads of thermal mass, excess heat from the fire slowly accumulates, requiring less and less fuel the longer the oven is in use. This is why the barrel oven is sometimes referred to as a "mixed" oven, since it combines the best of both types of ovens: direct- and retained-heat. In other words, it's the Prius of wood-fired ovens.
Here's what the barrel oven looks like on the inside:
This was the other aspect that grabbed my attention: because the fire is separated from the oven itself, and because the cooking chamber of the oven itself doesn't need to be made from thick, dense materials, there's loads more room for baking compared to most dome ovens, which have just a single deck. The design of the barrel oven includes two sliding shelves, each large enough to hold two 13"-by-18" half-sheet pans, or one full sheet. That's enough room for eight to ten 1-kilo loaves of bread, or four 12-inch pizzas at once. (It's also longer than it is wide, making it ideal for baguettes.) Contrast that with my lowly cob oven, which at best holds 4 loaves of bread or a single pizza at any one time.
Here's the thing you need to know about barrel ovens: they are a recent invention, and not quite ready for prime time. The first barrel ovens purportedly originated in Africa and were popularized in Argentina and Chile in the late 90's. They proved an important tool after the collapse of the Argentine economy in 2001, where they were promoted as low-cost and efficient ovens for small-scale commercial bakers. Unlike cob ovens, which can be made from common materials by just about anyone, the core of the barrel oven does involve some handiwork. While Firespeaking's design includes details like a double insulated door which requires welding ability, it is possible for a dedicated enthusiast to bolt together a simpler version. Moreover, unlike dome ovens, which have literally thousands of years of development behind them, the technology behind barrel ovens is in its infancy.
The Edlesons have built 4 barrel ovens around the States so far, with several more in the works right now, and they are in the process of starting to sell barrel oven kits—with all the necessary metalwork already assembled—for which they have a waiting list. The kits cost less than $1000, including shipping; the remaining materials (clay, straw, etc.) can be had cheaply, if not for free. They are also working on a pamphlet detailing how to build a barrel oven yourself, including the metalwork, due out by the end of this year (2011). They see the barrel oven as the ideal choice for small family run businesses or CSAs, but I can see it appealing equally to the home baker or pizzaiolo who—like me—wants something with more capacity and higher fuel efficiency. If you are interested in learning more about barrel ovens, check out their website, and be sure to sign up for their mailing list.
This stop-motion video, made at a recent barrel-oven building workshop taught by Eva Edleson in Asheville, NC this past spring, provides a great overview of the building process (which, once the parts and materials are accumulated, takes but a few days), as well as a good sense of how the oven functions: