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July 2003

By Jennifer Hicks
SPECIAL REPORT: Wood-Fired Ovens Take Center Stage

Sure, they can boost the ambience of your dining room, but that’s just one reason to look at wood-fired ovens.These units also offer fiercely fast cook times,flexibility and all the flavor you—and your customers—long for. 

Ever stand too close to the mouth of a wood-fired oven? If you got away with eyebrows unsinged, bully for you. These ovens are some of the hottest around, literally, and for many who buy, drama’s the draw. With one piece of equipment wrapped in a fancy designer façade, you can charm your customers with dancing flames, sizzling food, wood-roasting aroma. You get the idea.

But the reasons to consider a wood-fired oven go way beyond the drama. The intense heat of these ovens produces benefits found in no other equipment. Fiercely hot, fast cooking seals in juices, caramelizes sugars, and produces full flavor profiles your customers—and your bottom line—can appreciate. And virtually no menu item is off limits.

And fact is, if you’re interested in the flexibility of a wood-fired oven, and don’t care so much about showing off for your customers, you can install back of house. Some operators buy these ovens purely for their capabilities and then haul them into the kitchen, where they get all the benefits of the technology but there’s no need for a designer outfit (or the architect’s fees).

When we quizzed suppliers about what to call these ovens, we found most prefer the term wood-fired or wood-burning oven, but one still favors the old-style “brick oven” name—from the low-tech days when ovens were indeed fashioned mostly from bricks—and another prefers the term “stone hearth oven.” What an oven’s called often comes down to the marketing goals of the supplier. The point is we’re talking about ovens with thick domes and floors made of some type of refractory material, plus the ability to burn wood, wood and gas together, or gas alone.

The long-time major suppliers of wood-fired ovens include Earthstone, Renato Inc., Rosito Bisani and Wood Stone Corp. Last year, a new entrant, Doughpro/Proprocess Corp., joined their ranks. Earthstone, Renato and Wood Stone all assemble in the United States, while Doughpro and Rosito Bisani import from Australia and Italy, respectively. All companies offer a range of standard models, some degree of customization, and single- and dual-fuel capabilities.

Which brings us to this point: Why would you want a “wood-fired” oven that uses gas alone? The oven’s design is really what you’re after, no matter if it’s fueling wood or gas, or a combination. The use of a refractory dome and floor plus really high heat—typically to 600&Mac251;F during peak production—creates a huge heat sink that cooks, uh, fairly quickly.

So, for example, during peak periods you can bake a pizza in a just a few minutes, roughly half the time that pie would be sitting in another type of oven. Or you can institute a diversified menu of broiled seafood or roasted chicken and meats, with cook times here also dramatically reduced. And since the oven retains much of its heat overnight—despite cutting off all fuel at day’s end—you can come in and bake bread or roast chickens in the morning even before the unit has been fired to full temp for the day.

That flexibility is what led Wildfire, a Lettuce Entertain You brand, to add wood-fired ovens to its equipment lineup. At the newest Wildfire, in Schaumburg, Ill., the wood-fired oven is “one of our most versatile pieces,” says Executive Chef Joe Decker, our cover subject. This unit, to be opened by the time you read this, will rely on its Wood Stone oven to turn out some of Wildfire’s signature dishes, including all of its seafood offerings, plus specialty pizzas and vegetables. Wildfire gets a fast, fiery roast from the oven, says Chef Decker, which seals in juices—a big plus for the fish dishes. When it’s open this Wildfire, the fifth unit in the chain, will seat 450 and serve an estimated 1,000 covers daily.

Kinda Like A Clay House
Wood-fired oven design has evolved over many decades, but the basic principle remains the same. Thick, domed walls offer high thermal mass, which generates a thermal flywheel effect, meaning that the walls’ mass moderates temperature swings and maintains temp consistency over time. It’s the same principle that makes adobe houses efficient, comfortable structures.

The first wood-fired ovens appeared in North America in the 17th century for use in homes. Commercial use cropped up in the late 19th or early 20th century. Decades later, in the 1970s, California-style pizza baked in a wood-fired oven made its debut, setting up this style of oven as a flexible, flavor-nurturing alternative to traditional pizza deck ovens. Today the wood-fired oven’s flexibility is utilized in countless casual-dining chains, hotels and pizzerias.

If you stripped away the fancy façade found around most wood-fired ovens, you’d find some common elements, no matter the model: a domed interior and thick floor made of tough refractory material; a domed front opening, and a steel shell covering the works. In ovens that make use of gas, you’d find at least one burner. And some ovens also offer some form of insulation.

The differences in today’s ovens appear mostly in the materials used, and how the ovens are manufactured. Domes can be fashioned of such materials as alumina—the unrefined precursor of aluminum—combined with another refractory agent; high-temp ceramic, or refractory cement, which contains some lesser degree of alumina in most cases. Domes are either cast as one piece or several pieces that are then fitted together.

Floors can be set as separate bricks or tiles, or cast as one or several larger pieces. Materials include alumina, ceramic, cordierite—a magnesium alumina silicate material—or a combination of clay, alumina and refractory sand.

There are two schools of thought when it comes to brick/tile and one-piece flooring. Those who favor brick or tile claim that in the event of stress fractures, it’s easier to replace these smaller pieces than a one-piece floor. Meanwhile the one-piece proponents believe there’s better heat retention in a single floor because the no-brick design means no gaps between heat-conducting materials. We’ll leave you to sort out those opinions on your own.

Insulation is another point of differentiation. Some oven makers put insulation between the dome and the steel shell, in the form of a spun ceramic fiber or a cast mixture of pearlite and cement. Still other makers instruct you to wrap your oven in a blanket of insulation before enshrouding the works in a façade. We’ll detail insulation further when we discuss individual suppliers.

Keep in mind that no matter who makes it, a wood-fired oven is a hefty acquisition. Standard ovens run from 3’ to 8’ in width and weigh several thousand pounds. You’ll be looking at a price tag beginning at $6,500 for an “off-the-shelf” model and ending somewhere beyond $20,000, depending on how much customization you’re after. Typically your baseline model fires wood alone, and as you add gas—either to assist the wood or as a single fuel—price increases. And remember that you’ll want to budget for a façade—designed by your architect and built onsite—if you install in sight of the dining area.

Firing Up The Big Boys
An alphabetical run-down of who makes what begins with the company that’s been in the U.S. market the least amount of time. Doughpro/Proprocess Corp. began selling wood-fired ovens about a year ago; it commissions each oven from J.W. Beech Pty. Ltd. of Brisbane, Australia, which has been selling this type of oven worldwide for 12 years.

Doughpro construction veers away from traditional manufacturing, which requires the casting of domes before the steel shell goes on. In this process, a 1&Mac218;4”-thick steel shell is constructed with a front opening and rebars—steel reinforcing bars—mounted inside. Then refractory cement is poured in to a thickness of 8” to 14” in different areas. Thus the dome material hardens right inside of its shell, with the rebars helping hold everything in place. The floor is made of 3”-high alumina bricks, each 6” x 12”.

Fuel options include wood or gas alone, and wood with gas assist. When adding gas to a wood-fired model, you get one burner rated at 76,000 Btu. With the gas-only option you get up to three burners and up to 228,000 Btus. The distance between floor and dome is 151&Mac218;4”.

While Doughpro’s standard ovens come round, you can also order rectangle- and even triangular-shaped custom units. And since the steel shell is made first, you can also spec additional windows, for visual appeal or to add a slot for chargrilling.

These ovens arrive in two pieces, which makes maneuvering through doorways a little easier. Once put together, you can wrap the ovens in insulation before building a façade. Doughpro offers a 4-year warranty.

Next alphabetically, Earthstone Wood-Fire Ovens comes to market with five standard models ranging from 3’ to 7’ wide. Fuel options include wood or gas alone and wood with gas assist.

Round domes are cast from a mixture of 80% alumina and 20% refractory aggregate with special additives that protect walls from the acidic byproducts of burning wood. Earthstone then prepares an insulating material made of a hardened, lightweight combination of pearlite and cement that has the consistency of Styrofoam when it’s heated. This material fills a void area from 4” to 20” between dome and steel skin, forming a secondary molded body of insulation. The company says the combination of the 4”- to 6”-thick alumina dome and pearlite/cement insulation maximizes the dome’s thermal mass for good heat retention and efficiency.

For its floors, Earthstone mixes alumina, clay and refractory sand, presses the mixture into tiles at 8,000 psi, and then kiln-fires them at 2,800&Mac251;F until they ceramitize. Tiles measure 12” x 12”, and 11&Mac218;2” thick. As for burners, you’ll find one rated at anywhere from 90,000 Btu to 170,000 Btu, depending on the size of the oven. Finally, Earthstone promotes its 5-year limited warranty, the longest in this group.

Meanwhile, Renato Inc. offers 10 standard wood-fired models ranging from 3’ to 7’ wide. Domes are made of precast refractory cement, while bricks are made of a material called cordierite, a magnesium alumina silicate material. Cordierite offers a smooth surface, a low coefficient of thermal expansion, and excellent resistance to thermal shock, which is just what you’re looking for in an oven floor. Renato purchases the preformed bricks from a supplier; each brick measures 24” x 24”.

Fuel options include wood, gas or both. Smaller Renato ovens come with one burner, and you can step up to two burners in larger units. Btu ratings range from 25,000 to 66,000. Also, you can outfit these ovens with an infrared gas burner beneath the oven floor to maintain the desired floor temperature. The company originally added this feature to cater to bread bakers, who typically need a stable floor temp for proper bread baking, but it works for just about everyone else, too. A separate thermostat controls the under-floor burner.

Two special features keep the introduction of wood and the removal of ash out of the path of food. First, a second door at the back of the oven allows two different people to take charge of cooking upfront and adding wood at the back, a method Renato says promotes cleaner food handling. And second, an ash bin underneath the wood pile means no ash need be swept out the front of the oven during cleaning. The company recommends cleaning out the bin daily, but it can hold up to four days’ worth of ash if necessary.

Renato ovens offer interior dome-to-floor heights of 9” to 12”, and a limited 1-year warranty.

Rosito Bisani brings in its ovens from an Italian company called Forni Morello. Unlike its competitors, Rosito Bisani offers only single-fuel models; no wood-with-gas-assist option is available.

Domes are made of 95% alumina with a binding agent. The alumina mixture is vibrated during the curing process to remove air pockets and thus produce a solid, dense material. It’s then cast as five to seven separate pieces, each 7” thick, which are fitted together in tongue-and-groove fashion to create the dome. The steel shell goes on last.

Inside a Rosito Bisani oven you’ll find a three-piece alumina floor—a T-bar and two crescent-moon shaped slabs. So you get some of the benefits of a one-piece floor along with easy replacement, if needed. Slabs are 12” thick.

Of the standard models, you can choose from four options in 4’, 5’ and 6’ widths. You get one burner in each oven, rated at just under 72,000 Btu up to 120,000 Btu, depending on oven size. Height from floor to dome is 15”; all ovens come with a 1-year warranty.

And a final note: Rosito Bisani says that in ETL testing its ovens were found to require zero clearance for combustible materials. This means you’ll need no insulation around the oven before you install a façade.

Rounding out the list is Wood Stone Corp., which offers 10 stone hearth ovens in round, rectangle and square shapes, ranging from 5’ to 8’ in width. Your fuel options include wood alone, wood with gas, or gas alone.

Inside a Wood Stone oven you’ll find just two pieces: a 4”-thick dome and 4”-thick monolithic floor, both cast of high-temp ceramic. Beneath the floor there’s 4” of rigid insulation and an infrared burner, which has its own separate thermostatic controls.

Dome and hearth are connected by a carefully tensioned stainless steel exoskeleton, which ensures structural integrity. Also, the dome is wrapped in at least 2” of spun ceramic fiber insulation before it’s enclosed in steel.

In each of the smaller ovens you’ll get one burner rated at 70,000 Btu, while the larger models offer two burners each rated at 110,000 Btu or higher. Height from dome to floor is 20“-26”; Wood Stone’s warranty is 1 year. Also, all of Wood Stone’s components are engineered in the United States, and the company does its own casting.

A Word On The Environment
On to ventilation. Owning a wood-fired oven poses several challenges, including the age-old problem of how to vent your smoke and fumes. If you order a gas-only model, it can share hood space with any other equipment under a standard hood. No problem there.

But if you’re burning wood, the whole picture changes. NFPA 96 states that you cannot mix the byproducts of solid and nonsolid fuel in the same ventilation system. Thus, with a wood-burner you’ll need a chimney with natural draft going all the way to the roof or a hood with specs to suit wood fuel.

Wood-only cooking also requires a commitment to procuring good wood. Nearly any natural hardwood will work—cherry, oak, maple, mesquite, etc.—but it must be untreated. Treated wood—including most milled wood, say oven suppliers—adds chemicals to the cooking process. Stuff you don’t want.

Finally, keeping your oven in prime working condition takes very little effort. In all models, everything that’s left inside will incinerate eventually, leaving you with ash. Nearly all suppliers recommend you sweep out that ash daily. Renato, you will remember, provides an ash bin, to be emptied every day.

Most suppliers also recommend you make sure your burners haven’t clogged with food or debris. Schedule periodic burner cleaning with your service tech.

At day’s end, you either lay logs on the wood fire or turn out the gas, put night doors in place and go home. Overnight the oven will cool somewhat, to a floor temp of roughly 400&Mac251;F, which means you’ll be able to come in early the next day and begin production even before you preheat—bread baking, chicken roasting, etc. Once you’ve fired the unit, it’ll take an hour and a half or so for the oven to come up to a peak operating temp of about 550&Mac251;F to 625&Mac251;F.

There’s more to know about wood-fired ovens, of course, but this basic guide should get you started. Bring your questions to these major suppliers.

Here’s who to call with wood-fired oven questions:

Doughpro/Proprocess Corp.

Earthstone Wood-Fire Ovens

Renato Inc.

Rosito Bisani

Wood Stone Corp.

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