November 2007
The Essence Of Speed
By: Mike Sherer

Whether you're looking at traditional microwave ovens or combi versions that add a convection or radiant heat component, today's microwave technology makes short work of many cooking applications.

Like most pieces of equipment in your kitchens, microwave ovens do some tasks extremely well, but they can't do everything. With both traditional microwaves and combination microwaves on the market today, the trick to specifying one is to figure out how your stores will be using them and then go after the units you need.

As a refresher, microwaves are waves of electromagnetic energy that travel at the speed of light. When directed intensely at food, they interact with bipolar molecules, or molecules that have a positive charge at one end and a negative charge at the other, such as water, fat and salt molecules. The microwaves make these molecules rotate, and as they spin they bump into each other. The resulting friction creates heat, and the heat is conducted throughout the food, heating it or cooking it.

While technically sophisticated, microwave ovens have few parts. A transformer transfers power to a magnetron, which generates microwaves. An antenna or "wave guide" directs the electromagnetic waves into the oven cavity in a specific pattern. And a fan cools the components and exhausts heat from the cavity.

That's the science behind a microwave oven. The art of cooking in a microwave takes a little more time to learn. Microwaves are most effective at exciting water molecules, which means they heat/cook foods with high water content more effectively and faster than foods with a lower moisture content. It also means they are very effective as steamers.

With that in mind, applications are more readily apparent. Traditional microwaves are great for defrosting frozen foods, reheating chilled foods, steaming small batches of vegetables, heating side dishes, and finishing meats or other entrées to a desired degree of doneness. Combination microwave ovens—units that add convection or radiant heat to a microwave oven—have even broader applications.

The Need For Speed
The big advantage of a microwave, of course, is speed, which is why most restaurants, including the Bob Evans Restaurant in Merrillville, Ind., where we shot our cover, have at least one. Convection, radiant heat and steam heat all cook food from the outside in, as heat is transferred to the food product and conducted to its center. Microwaves cook foods using molecular friction inside the food itself to create heat and conduct it throughout the food. Add a little water inside the oven and microwaves will quickly turn it to steam, creating additional heat within the cavity to cook even faster.

Contrary to popular belief, microwaves don't actually cook food from the inside out. While microwaves do penetrate much deeper into food than do convection heat or infrared radiation, they lose about half their power for every three-fourths of an inch they penetrate. By the time they reach the center of a six-inch bird, roast or casserole, for example, they've essentially disappeared, transferring all their energy into the food.

Depending on the item, though, foods typically cook two to four times faster in a microwave than in conventional equipment. That means you can quickly cook small batches of food to order. Pre-cut and portion all your vegetables, for example, and you can steam a plate of vegetables to order as entrées come off the broiler or out of the oven. Another approach: Some chefs use microwaves to pre-heat thick cuts of meat that patrons order well done so they can go on the broiler at the same time as those that other patrons at the table ordered rare or medium rare. And some cooks quickly finish all types of entrées in the microwave.

A Question Of Power
Like most equipment, with microwaves power equals speed. The more powerful the stream of microwaves directed at the food, the faster the food will cook. A small consumer microwave may operate on about 600W. Light-duty commercial microwaves usually start at about 1000W, and heavy-duty ovens range from 1600W to 3000W.

That may sound like a lot of power, but microwaves are pretty energy efficient. The first microwave oven ever built was 6 ft. tall, weighed 750 lbs. and used 3000W, about three times a typical consumer or light-duty commercial microwave today. An early commercial model, introduced in 1954, generated about 1600W and cost around $3,000.

Sometimes, however, you don't need all that power. For defrosting or gently reheating items, you need lower power settings. Most microwave models give you 10 power settings. Some offer as few as four. More is usually better so you have flexibility.

Some commercial have two magnetrons, and some even have four. One advantage of multiple magnetrons is that if a magnetron fails, the oven will still operate, albeit more slowly since it will cook at only half power. Another advantage is even cooking.

Almost all foods have different thicknesses, different densities and irregular shapes that will cause them to cook unevenly. Because microwaves cook by creating heat within food products themselves, water content, fat content and product density all affect how evenly products cook. And since they cook so quickly, any unevenness in the cooking process can be magnified.

Microwave oven manufacturers address this challenge in a few different ways. The key is spreading the microwaves more evenly throughout the oven cavity. One way to do that is by adjusting the antenna or "wave guide." Designing the antenna to create the right pattern of microwaves inside the oven is more art than science. Some models use a rotating antenna to spread microwaves more evenly throughout the cavity (the same reason some consumer models use a rotating plate to turn the food).

Another way is by adding a magnetron. Not only does that increase the concentration of microwaves, it also allows manufacturers to launch microwaves into the oven from different directions. Most ovens launch microwaves from the top, directing energy down into the food. Makers of dual-magnetron ovens typically mount one above and one below the oven cavity, so microwaves are directed at the top and bottom of the food.

Finally, the oven cavity itself is designed to help spread microwaves. Microwaves can't penetrate metal. They reflect off the metal walls of the oven cavity and back into the food. Cavity size and shape are usually matched with the antenna to produce the best dispersal and concentration of microwaves into the food.

Keeping It Under Control
You can't throw all those microwaves at the food, though, without some control. Just as you wouldn't drive a Shelby GT without good brakes, you wouldn't want to run a powerful microwave without a way to adapt it to different foods.

Because microwaves heat from the inside instead of with an external heat source, you really cook with time as opposed to heat. As mentioned earlier, most ovens offer power settings, giving you some control over "heat." But even using power settings, foods will still cook in a fraction of the time they take using conventional cooking equipment. A few extra minutes in a conventional oven may not overcook an item. A few extra minutes in a microwave could be disastrous.

Digital controls make it easy to key in a set amount of time to cook a product as well as the power settings you want to use. Most models on the market today have touch pad push-button controls to set power and time and LED displays to indicate settings and time remaining. A few models still offer analog electromechanical timers, but they may not be as accurate or give you as precise a setting as you may want.

Most models also are programmable, allowing you to pre-program a cook cycle that employees can access with the push of a button. These usually let you program three-stage cooking, too, giving you the ability to defrost, warm and cook frozen products in one step. Some memory pads hold up to 16 programs, others up to 20. Another nice feature is a button on some models that automatically calculates cook time when you put two portions of the same item in the oven.

Models with digital controls and displays typically have self-diagnostics that alert you when something is wrong. And all units have a safety interlock that automatically shuts the oven off if the door is open.

The door, in fact, is one of the few moving parts you have to even think about, let alone worry about. Most models have doors that open left to right, so you don't even have to worry about specifying right- or left-hand hinges. A few models, particularly those with larger capacity to hold half-size 6-in. hotel pans, open from top down.

Most have grab and pull handles. Try to stay away from handles with latches built in. Doors tend to get a lot of use—most manufacturers test them 250,000 to 400,000 times—so a handle with moving parts will likely fail before a simple grab and pull handle.

A Little TLC
Microwaves also are pretty easy to care for. Keep the interior clean as you should with all ovens. It's particularly important in microwaves. They dry out stuck-on foods completely, and carbonize it. The dried foods can disrupt the magnetron or cause fires inside the oven.

Cover foods when you cook them in a microwave. Not only does covering food speed cooking and even it out, it keeps food moist. Best of all, it keeps food from splattering on oven walls and ceiling, making it easier to keep clean.

Most commercial models have a removable air filter to keep dust and grease out of the components. Clean the filter regularly to help keep components cool and prevent the fan motor from working too hard.

Use only microwave-safe plastics in your microwave oven. Don't use metal pans. Since microwaves reflect off metal, any metal that's too close to a magnetron can bounce microwaves back into the magnetron and damage it. Aluminum or tin foil has so many reflective surfaces when it's crinkled that microwaves bounce all over the cavity.

Technically, you can use metal in a microwave oven in certain situations. In an oven with a top-mounted magnetron, for example, if you put food in a metal pan, the pan will act much like the bottom of the oven. Newer models launch microwaves from the sides of the oven, so they don't reflect off shallow metal pans, meaning you can use standard hotel pans.

An important thing to look for in a supplier is a good support network. Microwaves have become so reliable that some manufacturers offer 3-year warranties on parts, labor and travel. Nevertheless, pick a supplier with a good customer service department, local service reps who can readily fix problems, a strong R&D department to help address solutions specific to your operation, and on-staff chefs to help train your managers how to use and program their ovens with your menu items.

And while microwave ovens will cook a wide variety of foods, there are many things they don't do well. They don't brown foods, and don't do baked goods very well. So these days manufacturers are designing ovens for specific products. More often, on new models you'll see controls programmed to defrost, heat and/or cook specific menu items. And manufacturers are more than willing to work with you to tweak an oven for your proprietary applications.

Turn now to our Microwave Technology Gallery for a look at the latest microwave and combination microwave ovens on the market. All have been introduced in the last several years, and there's even a brand new entrant in the category.

Some Speedy New Combinations
Several manufacturers now offer combination microwaves that include convection heat, an infrared heating element, or both. The obvious advantage is that convection and/or radiant heat browns foods, making them more appealing. These ovens also produce dry heat, letting you carry out an even broader range of tasks, such as roasting or broiling meat and poultry, baking pizza or bread, or toasting sandwiches.

An even bigger advantage, though, is increased speed. Convection and/or radiant heat combined with microwave cooking can speed the cooking process by 10 to 15 times when compared to conventional cooking equipment such as standard convection ovens. A thick salmon fillet or beef tenderloin might take 20 to 25 minutes in a convection oven. Some of the new microwave combos can cut that time to about 2 minutes and 15 seconds.

Yet another advantage of many of these models is that although they still have a small footprint and fit on a countertop, they have the capacity for one or two standard hotel pans. And given their speed, that means they can produce the same volume of food as a 10-pan convection oven in the same amount of time, say suppliers.

There are three variations on theme with this type of microwave combination oven. One combines high-speed convection heat with the microwave. Another adds an IR heating element to that combination for increased browning. Makers of these two types of ovens also build a catalytic converter into the units for ventless cooking. You can put them anywhere in the kitchen since they don't need to be placed under a hood.

One manufacturer makes a third type of combination oven that adds microwave-assisted cooking to a traditional combi oven. The result is an incredibly versatile humidity-controlled convection oven that cooks very fast. It also has a 10-pan capacity, so it can churn out high volumes of food in a short time. Though stackable, the oven is a floor model that's designed to go under a hood.

Again, your choice will depend on your specific applications. Because all of these ovens use a combination of cooking techniques and cook so quickly that slight variations in time or power can result in improperly cooked product, all of them have sophisticated programmable controls with enough memory to store a hundred or more cooking cycle recipes. A couple of models let you store these recipes on a memory card or key that you can use to program additional ovens. You can even program the floor model unit with a personal computer.

When you spec these combination microwave units consider the same factors you'd consider when spec'ing a traditional microwave oven: power, controls, number and placement of magnetrons, type of wave guide, versatility, programmability, ease of use, and serviceability.

Check with manufacturers on the warranties they offer, and ask about their warranty service records to get an idea of reliability and any challenges you might face.

Ultimately, the best way to find out which of these speed demons is right for your operation is to ask manufacturers for demonstrations using your menu items. Get cooking!

Microwave Myths
Don't believe everything you read or hear about microwave ovens. There are two persistent myths about them that suppliers wish they could dispel.

No nukes
Microwaves do not "nuke" food. That is, they do not emit ionizing radiation like X-rays or high-speed particles like gamma radiation. They generate electromagnetic energy waves that are between radio waves and radar in frequency. All microwave oven designs are thoroughly tested to make sure microwaves can't leak or escape the oven cavity. Doors all have safety interlocks that shut off the oven if the door is ajar.

Plastic containers don't cause cancer
Another common myth is that if you microwave food in plastic containers, the plastic will leach carcinogenic chemicals into the food. Certain plastics will melt if the food they contain gets hot enough in a microwave oven, and no one wants melted plastic in their food. But any plastic containers specifically marked "safe for microwaves" will not melt or leach chemicals into food.