There’s nothing quite like coming home to a fire on the hearth, the warmth and allure of the flames drawing us in. That’s one reason more and more healthcare facilities are making hearth ovens the centerpieces of their retail cafeterias. Perhaps more importantly, though, foodservice directors are finding that these show-stopping pieces of equipment aren’t just for pizza anymore.
While we may have started cooking over an open fire, for thousands of years we’ve cooked in stone or brick ovens, for good reason. The domed shape of these ovens captures the heat from the fire and reflects it back onto the food being cooked. And the stone or brick used to construct them acts like a heat sink, retaining heat and making the oven more efficient.
Today’s versions are even easier to use, and though they grew popular as pizza ovens they’re incredibly flexible and very fast. Healthcare operations are finding that the theater hearth ovens provide, along with the quality of foods cooked in them, help keep staff on campus for meals and increase traffic from outside their facilities.
Built Like A Brick…
The key concepts behind hearth ovens are the domed shape that captures and reflects heat back down to the floor of the oven, and the refractory, or heat-resistant, materials used to construct them. They allow these ovens to get as hot as 900°F to 1,000°F, far hotter than most commercial ovens.
Manufacturers use basically three types of materials for oven interiors—red clay brick, alumina ceramic tile or cast ceramic. Aluminum oxide is the compound in clay and ceramic that makes them resist heat. The higher the alumina content the denser the material and more heat resistant.
Wood-and coal-fired ovens built in Italy nearly a hundred years ago used red clay bricks because the material was plentiful and high enough in aluminum oxide content to make a good cooking oven (as opposed to an industrial kiln, which needs to withstand higher temperatures). Hearth ovens imported from Italy still use bricks like these.
Early ovens introduced here in the U.S. also used bricks, again because they’re easy to come by and have enough heat resistance to withstand high temperatures in wood-burning ovens. These bricks typically range in thickness from 2½ in. to 4 in., but can be placed on end to provide thicknesses of as much as 8 in. in spots.
The mortar that fills the gaps between bricks and helps hold them together is a different material, and can act as a barrier to heat conduction from one brick to the next. That has the potential to cause uneven heating across an oven floor. The constant expansion and contraction over time as an oven heats and cools can cause mortar to crack and fail, leading to the collapse of an oven dome. Though very rare, these types of catastrophic failures do occur.
Denser alumina tiles or bricks range in thickness from about 1½ in. on oven floors to 3 in. or 4 in. in the oven dome. The higher aluminum oxide content of these tiles means they don’t conduct heat quite as well as brick, and because mortar has to be used in oven construction, temperatures across the floor of an oven using tile, again, may be uneven.
The third type of construction uses cast ceramic material. One manufacturer casts the floors of its ovens in one piece, and the domes in another (using a proprietary formula for its ceramic material). That eliminates the many seams common to brick or tile ovens; fewer seams means heat conducts more evenly through both the floor and the oven. Another maker casts its domes in one piece, but uses large alumina tiles for its oven floors. Cast floors can be up to 6-in. thick, and cast domes as much as 4 in. or more.
One drawback of cast ceramic is that cracks tend to form from expansion and contraction. They look unsightly, but when the oven heats up again, they close up as the material expands from the heat again.
Hold That Heat
With temperatures ranging from 575°F up to 1,000°F, hearth ovens obviously get hot. Various types of insulation are used to hold that heat, making the oven more efficient and preventing the ambient room temperature from getting warmer.
Hearth floors typically sit on an insulation board, which then sits on ¼-in. mild steel. Domes are encased most often in ¼-in. mild steel, but at least one maker uses stainless around the dome. Manufacturers insulate the gap between the brick or ceramic dome and the steel casing.
Some manufacturers, whose ovens operate at somewhat lower temperatures, use a foamed-in-place insulation. Others use a ceramic-fiber wool insulation, typically effective at higher temperatures. Some use a combination of ceramic wool and solid ceramic pieces depending on oven design.
The thinking behind each is not only how to retain heat inside the oven, but also where to place insulation and how thick it has to be to do its job while creating the most cooking area in the smallest footprint possible.
The other reason to insulate as well as possible is to enable you to install the façade of your choice. Obviously, you’ll want the oven to fit in with the overall design of your servery or cafeteria. Manufacturers try to make it as easy as possible to add whatever material you want to the exterior of the oven, including tile, stone, wood, metal and more. If you want stucco, manufacturers will even ship your oven encased in wire mesh, ready to finish.
Insulation here is key. One manufacturer claims that its insulation is so effective you can use combustible exterior materials (such as wood) with 1 in. of clearance. Another manufacturer needs 3 in. of clearance for non-combustible materials. That not only affects the design process but also the amount of space you may need for the oven, all considerations to take into account before you select and order one.
Fire It Up
Traditionally, hearth ovens were wood-fired, and some old-world Neapolitan-style pizza parlors, particularly on the East Coast, still insist on coal-fired ovens. These days, you have a lot of choices. The key, really, is having a fire, or flames, on the hearth. Wood smoke, especially from fragrant woods such as apple or mesquite, adds flavor to food. But it’s really the caramelization from the flames and the heat of the oven that provide most of the flavor in food cooked in hearth ovens.
The fire on the hearth also heats the air in the dome, heating the dome itself, which reflects that heat back down into the floor. The hearth fire also conducts its heat through the floor. When both oven floor and dome are hot, they cook food quickly and impart lots of flavor in the process.
Coal-fired ovens are the most difficult to use since coal fires are more difficult to light, and they require more tending to keep the coals banked and hot. Woodfired ovens, on the other hand, are relatively easy to operate even though they might seem to need as much care and attention as coal-fired ovens. Most makers say that employees can learn the basics of starting and tending a wood fire in about 15 minutes, and can be proficient cooks with a little practice and common sense.
You can also spec hearth ovens as a wood/gas combination or solely gas-fired. With both there are differences from model to model and from maker to maker. Gas-fired ovens come equipped with one or combinations of three types of burners.
One type is what’s sometimes called a “torch” burner or atmospheric burner. Torch burners stick up from the floor into the oven and produce a high amount of Btu as their job is to heat the oven. Atmospheric burners are effective, but tend to be noisy.
Display burners are straight-line burners that look much like those in a gas fireplace. And, in fact, many manufacturers add ceramic “logs” to give them the look of a wood-fired oven. These burners also serve as the primary heat source for many models, but some models may offer the combination of a torch and a display burner.
You can find a third type of burner on some models that’s designed to help maintain both the floor temperature as well as air temperature in the oven. In some cases, makers mount an infrared (IR) burner beneath the floor for operators who expect times of extremely high volume. Remember that in most hearth ovens, the fire or flame on the hearth heats both floor and dome, and the dome’s heat also is reflected back down to the floor. When product such as pizza covers the entire floor of the oven, it may lose some of its temperature. An IR burner beneath the floor ensures more constant, even temperatures. A thermostat in the floor regulates the burner’s operation.
In wood/gas combinations, manufacturers add either a torch burner or an under-floor IR burner as the gas assist. These models also have somewhat more precise temperature control, since the gas burner will turn off if the wood fire is heating the oven adequately.
Down To Size
Hearth ovens are traditionally round, with a single opening. These round models can range in size from about 48 in. in diameter up to 90 in. or more. Round ovens make terrific show pieces in the center of a servery, for example, if you have the space, but also fit well into corners.
Several makers also offer rectangular versions that work well on cooklines, for example, or where space is more limited. Rectangular ovens often have two openings, and if piped for gas, can come with different burner configurations, allowing you to cook a little differently on each end of the oven, for example.
Capacities range from about six, 8-in. personal pizzas or two, large 16-in. pizzas in smaller ovens to around 20, 8-in. pizzas or seven to eight, 16-in. pizzas. Depending on how hot the oven gets, thickness of your pizza crust and amount of toppings, cook time can range from two to six minutes or so. Factor the size you need by determining how many pizzas you’ll need per hour during peak periods, for example, and divide by the cook time and the number of pizzas that the oven will hold based on diameter to get an idea of the size oven you’ll need.
Take A Deep Breath
Manufacturers vent oven models differently. The vent on many round models is in the eyebrow over the opening, but some models locate it in the dome. Likewise, rectangular models may vent exhaust from different locations on the oven depending on model.
Gas-only ovens can be grouped with other cooking equipment under a central Type I ventilation hood. Ovens burning solid fuel (wood, coal or combination wood/ gas) must have their own Type I ventilation hood and ductwork. Ovens that burn solid fuel generate more soot and other compounds such as creosote that can build up quickly in hoods and ductwork. They have to be cleaned more often to prevent the possibility of fire.
Cleaning the ovens themselves is a snap. They tend to burn hot enough that all they require is ash removal each day with a brush. Obviously, wood-fired ovens will have more ash to clean out than gas ovens, but the job is simple. If you do experience any kind of buildup from food grease, heating the oven to about 575°F for an hour will turn the residue to ash.
These ovens will run you anywhere from about $12,000 to more than $30,000, or about $16,000 to $45,000 with installation. They’re not inexpensive, but they cook as fast or faster than conveyor or deck ovens, and produce great food quality and flavor. And the theater they provide should increase traffic enough to justify their cost.
The best time to install them is at the same time as a walk-in, before the space has been walled in. These ovens weigh anywhere from 1,000 lb. to 6,000 lb., and they’re quite large. Some manufacturers construct them in two or three sections to make them easier to fit through existing doorways. But at least one manufacturer constructs ovens in a single unit. Most can be moved by forklift and even pallet jack, but if you plan ahead, often setting the oven in place with a crane is easiest.
As originally printed in FER Magazine fermag.com
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