Foodservice Equipment Reports

SPECIAL REPORT: Bringing The Heat

If there are two things operators almost universally clamor for, they’re speed and consistency. You can get speed a lot of ways. Throw a lot of Btus or kWs at a product, and you can cook it faster. If you move the air around inside the cooking cavity, as convection ovens do, and that works too. Add steam, if you want to retain moisture and/or increase speed, and shazaam, a combi oven cooks some items in half the time of a conventional oven.

How about consistency? One way is a conveyor running at a constant speed. One oven manufacturer, in fact, introduced a conveyor oven as far back as the 1880s. Some 90 years later, the modern version appeared, running a conveyor belt through the oven like a number of commercial food processors do.

Then a clever fellow by the name of Don Paul Smith patented a cooking process called impingement. In an impingement oven, air is forced through small nozzles, or fingers, directed at the food on the conveyor. The stream of air pushes away the barrier of cold air and moisture surrounding the product, allowing heat to transfer more quickly. Suddenly, impingement meant cook times shrank faster than a pile of chips at a craps table.

Smith’s company licensed the technology to two equipment manufacturers, and for many years, the market for conveyor ovens was divided into super-fast impingement ovens, made by those two players, and also fast non-impingement conveyor ovens made by others. In the late 1990s, however, the patents on impingement cooking expired, leaving the field wide open.

As manufacturers worked on their own versions of impingement or other airflow concepts, they found another rising concern among operators—the cost of energy. Conveyor oven makers saw an opportunity to jump in with both new impingement models and models that saved energy. The result is a market that today offers you a lot of choices that fit just about any application you’ve got.

Conveyor ovens primarily use three technologies—impingement, radiant heat, or a combination of the two. Which you choose depends on what you plan to use the oven for. While all three types of ovens are capable of cooking a wide range of products, each has its specific strengths.

Ovens that use either quartz or cal-rod elements to produce radiant heat are best at toasting, melting, and grilling or broiling. Ovens that use impingement do an excellent job of baking—pizza, cookies, pies, bread, etc. Ovens that use a combination obviously have a lot of versatility.

Since their invention, impingement ovens have dominated the conveyor market, giving pizza chains quality, consistency, greater throughput and reliability. For a long time, though, operators had limited choices in how they managed and manipulated the cooking process for different products. Airflow in the ovens was pretty much established by the design of the fingers. All you could control in the cook cycle was time and temperature.

But what if you wanted to add a menu item that requires a very different treatment? Oven makers have addressed that with a variety of features that allow you to handle varying product needs. Oven makers now often offer different finger or nozzle plate designs for different types of products. Since most fingers can be removed for cleaning, you can exchange one set for another in the field. At least one manufacturer now makes impingement ovens with adjustable fingers that let you change the oven’s cooking profile more easily.

Most conveyor ovens, though, can handle different products at the same time in a couple of other ways. Many models offer split conveyor belts as an option, letting you run one product through faster or slower than another depending on its cook time. Other models have a door in front, often called a “sandwich window,” that lets you put product in the oven halfway through the conveyor’s pass.

New models give you even more control. Digital controls let you program time and temperature specs for different products. Push a button to set the parameters for pizza, for example, and another button to cook a batch of cookies or fresh breadsticks.

One manufacturer makes ovens with different zones that allow you to change air velocity in different parts of the oven, providing a more customized bake or cook cycle for each of your menu items.

Yet another offers an oven with two separate blowers. Typically impingement ovens have one blower that forces air through the fingers so about 60% flows from the bottom and 40% flows from the top. By using two blowers with variable-speed fans, this oven allows you to move more air at the product for faster cook times, customize how much air you move to allow for different types of foods, and move air throughout the oven to cook all the way to the product edges and provide consistency.

Radiating Heat

Conveyor ovens that use a radiant-heat source were developed when oven makers started producing countertop versions of their bigger models. Many models are essentially conveyor toasters on steroids—more powerful versions of infrared toasters that can bake as well as heat and toast. Ideal for small sandwich shops, c-stores and a range of other operations, these smaller units offer a lot of versatility in a relatively small footprint.

But radiant-heat conveyor ovens have grown, both in size and popularity. Now some models rival impingement ovens in speed and throughput. While most radiant-heat ovens tend to be countertop models, there are now floor versions available as well. One advantage, according to manufacturers, is that radiant-heat ovens have fewer moving parts (no blowers) to provide simpler, quieter operation and excellent reliability.

In addition to making larger radiant-heat models, a couple of makers have taken new and slightly different approaches to this type of conveyor oven. One is a combination gas/electric radiant-heat oven. The other is a combination radiant-heat and impingement oven.

The gas-electric combo uses gas-fired infrared burners on the bottom that reputedly furnish as much heat as a deck oven, and electric elements on top that provide browning and melting to “finish” products. The maker cites quiet operation and greater reliability due to fewer moving parts as key benefits, along with high-heat capability.

The other hybrid oven combines the speed of impingement cooking with the browning characteristics of radiant heat in a countertop model. The manufacturer had customers who wanted to speed production of sandwich items. Impingement brought the time needed to heat refrigerated sandwiches down to about 25 secs. from 45 to 50 secs., and the radiant elements on both top and bottom toast sandwiches at the same time. Another customer now uses the oven to bake pita bread in its stores.

Power Vs. Energy Savings

Speed of cooking used to come at a price. Like fast cars, conveyor ovens burned through fuel quickly. But manufacturers have made significant strides in energy-efficient design. Here are a few of the tricks they’ve incorporated that trim energy use without sacrificing performance.

Better burners. Newer gas models use burners that are more efficient. One oven manufacturer also makes its own burners rather than sourcing outside. The all-stainless atmospheric burner doesn’t require a fan or moving parts, making it more reliable and quiet than some other burners.

Energy-management systems. Several models feature systems that monitor the oven cavity and automatically put the oven in idle mode when there is no product in the oven. Others have a manual switch that puts them in sleep or idle mode.

Better air circulation. Smarter airflow designs help save energy in two ways. A good pattern of impingement nozzles, or the ability to control air velocity with variable-speed blowers or zones, do a better job of removing the barrier of cold air and moisture that surrounds food as it’s cooked. That allows you to cook at a lower temperature, which saves energy.

Efficiently circulating that air through return vents also can make a difference in how hard blowers have to work, which can save energy, too. A couple of manufacturers now claim better air management in their impingement models.

Insulation. Perhaps no surprise, when conveyor ovens first hit the market few operators were concerned about energy costs. As a result, ovens ran hot and inefficiently. Units now are insulated on all sides, providing an added benefit of increased safety since they’re cool to the touch (or at least not capable of third-degree burns like in the old days). One maker even cooks in a powder-coated oven at trade shows to demonstrate how cool the oven’s exterior is.

More efficient components. In recent years, electronically commutated motors have made belt drives and blower fans much more efficient. Fan-blade design also has made blowers more efficient.

All of these improvements, though small on their own, have resulted in ovens that cook 30% faster with 30% less energy than older models. Those kinds of numbers defy the notion that power and energy savings are mutually exclusive.

Sizing Up Your Specs

Now down to the nitty-gritty. Like almost any other piece of equipment you buy, of course, which oven you choose depends on its intended application. As mentioned earlier, radiant-heat ovens tend to be better at heating and browning while impingement ovens tend to be better at baking. So your first consideration is what types of products you plan to heat or cook in the oven.

Next question is how much product you intend to cook and how fast. Oven throughput not only depends on the size of the oven and how fast it can cook, but what products you plan on sending through it. Pan pizzas, for example, take longer to cook than thin-crust. So how many pizzas per hour an oven can cook may vary dramatically from one operation to another.

Most models these days are stackable, so even if you overestimate how much product you can put through an oven during your rush periods, you can always stack another without destroying your floorplan.

Size not only affects throughput. If you plan on making 18” pizzas, obviously an oven with a 16” conveyor belt won’t do you much good. Likewise, if you want to toast Dagwood-sized sandwiches, make sure you have enough clearance to fit them into the oven. Openings can vary from about 3” to around 6½”.

Another consideration when it comes to size is where you plan to put your ovens. Do you need floor models or countertop ovens? What size footprint do you have space for in your stores? Will you have to locate your ovens under a hood or not? Gas models always require a hood, but depending on the food you plan to cook, you may not need a hood for electric ovens, especially smaller countertop models.

A note about hoods. Some oven manufacturers are making placement in your operation a little easier by providing alternative ventilation solutions. One manufacturer has optional catalytic converters for its ovens, which eliminates the need for exhaust hoods. Another manufacturer offers a hood specifically built for its ovens that fits on top like a glove. The company will help you vent the hood to the outside and spec any necessary makeup air equipment.

Finally, make sure the oven you select has the flexibility you need for changing menus. That may mean specifying ovens with split belts, sandwich doors for half-pass cooking, or ovens that give you more cooking options than just time and temperature, like the hybrid radiant-gas models, those that provide cooking zones or variable-speed blowers, or those that allow you to change out the fingers/plates for different product profiles.

Construction And Control

Basic construction can determine how long your equipment will last and how reliably it will perform over time. Look for all-stainless construction using 300 series stainless steel. Some models use 400 series stainless in their construction, which may not be as durable under certain conditions.

Some makers use aluminized steel for some parts of their ovens, such as bottoms and rears where it’s not visible, to save costs. The problem is that rough treatment and caustic cleaning chemicals can eventually damage coated carbon steel like aluminized or galvanized steel. The coating can dissolve or be scraped off over time, leading to oxidation of the steel underneath.

Conveyor belts should be constructed of stainless and easily removable for cleaning. Look at bearings, too. Larger bearings tend to wear more slowly and fail less often than smaller bearings. Typical sizes in the industry are ½”, 5/8” and ¾”.

Conveyor drives vary from V-belts to chain drives or direct drive. Direct drive may give you both greater reliability and greater control over variable speeds. Ask manufacturers if their service agents have any data on failure rates of belt drives.

Belt direction obviously is important to the work flow in your operations. In some cases you have to specify belt direction so the factory can produce what you need. More models now give you the option of changing belt direction in the field. In some cases, that’s a mechanical fix that you’ll likely want a service rep to perform, but could be handled by someone on staff. On other models, changing belt direction is a software command that you can handle through the control panel.

The more control you have, of course, the more flexibility an oven can give you. Look for digital controls that make it easy to program time and temperature cycles. On some models, the digital control panel allows you to change the cooking profile of the oven (e.g., from baking off cookies to toasting sandwiches).

Look for easy disassembly/assembly of parts like the conveyor belt and fingers/plates (if the model is an impingement oven) to make cleaning easier. One manufacturer, for example, makes top and bottom plenums for its oven identical so there’s no confusion when employees reassemble the oven after cleaning.

Most units have crumb trays below the conveyor belt that can be removed and cleaned easily. Regular deep cleaning, however, will help you maintain the life of your equipment, and the easier it is to take apart, the more likely employees will follow a set cleaning schedule. Some ovens actually have a self-cleaning feature (if you really want to improve employee morale). Also, consider any options you may want, such as legs or casters, or items already mentioned like half-pass windows.

Finally take a look at warranties, availability of parts and service networks. As reliable as conveyor ovens are, (and one manufacturer estimates that 75% of the conveyor ovens it’s ever made are still in the field), they can still break down. Make sure that the supplier you pick has the warranty coverage and service you need to keep you up and running as fast as your ovens.

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