Along with radiation and conduction, convection is one of the three methods of heat transfer used in cooking. Typically, when professionals talk about convection cooking, they are referring to the circulation of hot air around food in an oven, but there are different types of convection cooking, and convection also applies to cooking with liquid or steam. Convection technology often improves traditional types of cooking equipment by shortening cooking times and improving results. Learning about convection cooking may help you better understand the various types of convection equipment available and help you make the best choices for your menu.
Three Heat Transfer Methods
- Radiation – Radiation occurs when energy in the form heat waves (infrared) hits the surface of food. Heat energy is transferred into the food and causes it to cook. Cooking equipment such as traditional ovens and toasters rely primarily on radiation. Heating elements don’t come into direct contact with the food. Instead, they turn red hot and “radiate” heat toward the food.
Microwave ovens also rely on radiation, but instead of emitting heat energy, they emit a form of non-visible light energy called electromagnetic radiation. Electromagnetic radiation hits food and excites the food molecules creating heat. The heat cooks the food.
- Conduction – Conduction occurs when food comes into direct contact with a heat source. Energy from the heat source moves directly into the food and causes it to cook. Placing food into a frying pan or onto the surface of a hot griddle are good examples. Cooking occurs at the point of contact and that is why foods such as pancakes and hamburgers are flipped half way through the cooking process. It allows both sides of the food to come into contact with the cooking surface. Conduction also occurs with liquids and steam. Carrots, dropped into pot of hot water cook by conduction. Heat energy goes directly from the water into the carrot. The same with a steamer. Carrots placed in a steamer cook via direct contact with the steam.
- Convection – Convection occurs when a heated medium, such as hot air, steam, or liquid is put in motion around the food being cooked. While radiation and conduction are static processes, convection is a dynamic process. The heat source needs to be moving. In the case of a traditional oven, you do that by adding a fan to the cooking compartment. That circulates hot air around the food.
A roast sitting in a traditional oven will have a thin envelope of cooler air surrounding its surface. That is because the roast is absorbing heat from the adjacent layer of air. When a fan is added to the oven, circulating hot air strips the envelope of cooler air away from the roast replacing it with hotter air. That speeds up the cooking process. With liquids, convection is achieved simply by stirring the pot, or by allowing it to reach a rolling boil.
The convection oven is the most common example of convection cooking equipment in the commercial foodservice industry. The concept is simple. Begin with a traditional oven and add a fan to circulate the hot air. Over the decades, manufacturers have invested enormous amounts of research and technology into perfecting the original concept. Modern convection ovens outperform traditional ovens on nearly every level.
Convection ovens typically cook 25% faster than traditional ovens, at temperatures that are 25 degrees lower. That saves time and energy. Additionally, convection ovens cook with dry heat that provides superior and more even browning. Traditional ovens have hot spots. Convection ovens provide even temperature distribution throughout the oven cavity so there is no need to turn pans mid-bake or swap rack positions.
- Traditional Convection Ovens – Just like traditional ovens, traditional convection ovens usually have two heating elements: one on top and one on the bottom. They also have a fan, usually mounted in the rear of the oven compartment. The fan simply circulates hot air generated by the heating elements. These are sometimes called “American” convection ovens.
- True Convection Ovens – True convection ovens feature a third heating element mounted immediately behind the fan. With true convection ovens, the fan not only circulates hot air generated by the heating elements, it blows additional hot air directly onto the food. These ovens heat up faster, recover faster, and further reduce cooking times. They are sometimes called “European” convection ovens.
- Convection Ovens With Steam – Several manufacturers offer convection ovens with a steam feature that allows operators to add additional humidity to the baking compartment if desirable. Convection ovens generate dry heat, and while skilled users can adjust time, temperature, and ingredients to compensate, there may still be recipes that yield better results with more humidity in the cooking compartment. Convection ovens with steam offer that option. They are not designed for full-steam cooking and should not be confused with combi ovens (discussed below). They simply add some moisture to the cooking compartment when needed.
- Dual Speed Convection Ovens – Convection fans blowing across delicate items like custards, soufflés, cakes, and some breads, may cause lopsided or overly dry results. Dual speed units offer a slow fan speed for delicate baking, and a high fan speed for roasting. Most all convection ovens have the option to turn the fan off if you want to bake without convection heat.
Convection ovens are great for most roasting and baking needs including meats, vegetables, casseroles, cookies, pies, and pizza. Convection ovens come in a wide variety of sizes from small countertop models to large floor models mounted on legs. They can also be stacked two high. A convection option is often available as an upgrade when purchasing a traditional range/oven.
There are numerous price points, features, and configurations to choose from. Some convection ovens feature multiple fans, or fans that change direction to improve performance. Controls may be analog or digital with the ability to preprogram recipes. A Kitchen Spot Expert can help you select the best model for your needs from manufacturers like Admiral Craft, Atosa, Bakers Pride, Globe Food Equipment, Hatco, Moffat, Southbend, Star, Vulcan, or Waring.
When water is superheated, it is converted to steam. Traditional steamers (a.k.a., “steam ovens” or “steam cookers”) use steam instead of hot air to cook food. Convection steamers operate on the same principal as convection ovens, only instead of hot air, they circulate steam around the cooking compartment.
Steaming has many benefits. Steamed food retains more nutrients, vitamins, and minerals. It does not burn, scorch, or dry out. It requires no additional oils or fats. Steamed vegetables retain their vibrant colors and fresh appearance. Convection steaming shares all these same benefits, but does the job faster.
Many convection steamers are boilerless. Rather than a boiler connection, they feature a pan of water in the base of the unit and an onboard generator that coverts water to steam. The pan of water may be filled and emptied manually, or connected to a filtered water source and drain. Convection steamers do not cook under pressure, so the doors can be opened to add or remove food at any time, with quick recovery after the doors are closed.
Convection steamers are ideal for batch steaming, poaching, stewing, par-cooking, rethermalizing, and thawing frozen foods. Like convection ovens, they are available in a large variety of sizes and configurations with numerous features and option. A Kitchen Spot Expert can help you select the best convection steamer for your needs from manufacturers such as Accutemp, Cleveland, Crown Steam, Hobart, or Vulcan.
Combine a convection oven with a convection steamer and you get a combi oven. Combi ovens can be used in full convection mode for dry cooking, full steam mode for steaming, or both for ultimate control of heat and humidity. Combi ovens rely on convection fans to circulate hot air and/or steam around the cooking compartment. Time, temperature, and humidity (up to 100% inside the cooking chamber) are all adjustable.
Combi ovens cook faster. By combining convection heat with convection steam, you can cook at higher temperatures without losing moisture. Combi ovens also provide higher yields because food retains more moisture and shrinks less. Combi ovens are extremely versatile because they do the work of a traditional oven, a convection oven, and a steam oven using a single piece of equipment. That frees up kitchen space and saves on the original cost of equipping your kitchen. Combi ovens are also 30% more energy efficient than traditional ovens.
Many combis allow for pre-programmed multi-stage cooking. A food pan full of scalloped potatoes, for example, might be baked rapidly using both convection heat and steam. Then the steam can be evacuated from the oven and the dish can be browned and crisped using just convection heat. Finally, the heat can be lowered to an appropriate holding temperature with just enough moisture to maintain food quality until the dish is ready to be served, or cooled and stored.
Combi ovens are ideal for baking, roasting, steaming, boiling, stewing, braising, poaching, rethermalizing, thawing frozen foods, and more. Like convection ovens, they come in a wide variety of sizes and configuration with many different features. Like convection steamers, they typically generate their own steam, but usually require a filtered water connection for cooking, an unfiltered water connection for cleaning, and a drain. A Kitchen Spot Expert can help you choose the best combi oven for your needs from manufacturers like AccuTemp, Cleveland Range, Convotherm, Market Forge, Southbend, or Vulcan.
Convection Microwave Ovens
Several manufacturers have added convection cooking technology to microwave ovens. You can’t brown food in a microwave, and microwave ovens are notorious for uneven heating. Adding convection heat to a microwave oven solves both of those problems. With hot air circulating around inside of the oven compartment, you can brown food and eliminate hot spots.
When the microwave is running, you still can’t use metal pans or utensils inside the cooking chamber, and the door remains shut to contain electromagnetic radiation, but most convection microwave ovens can be operated in convection-only mode. Additionally, as with any microwave oven, you’re typically limited to cooking one dish at a time. Still, a creative chef can produce an enormous amount and variety of food in a small space using a carefully selected convection microwave oven.
Convection microwave ovens often fall under the category of “speed ovens” and are frequently used to prepare individual fast-food items like hot sandwiches, individual pizza slices, or side dishes. With browning capability, they are also great for many bakery products like cookies and brownies. They are popular in theaters, convenience stores, stadiums, snack bars, kiosks, delis, and fast-food operations. Manufacturers include ACP/Amana, Merrychef, and Panasonic. A Kitchen Spot Expert can help you determine if a convection microwave is a good choice for your commercial kitchen.
Impinger cooking is a specialized type of convection cooking. It is sometimes called “forced hot air cooking” because air is forced through a series of small air jets directed at the food. The pressurized hot air doesn’t just circulate around the food, it blasts the surface of the food for rapid heating. Impingement has traditionally been designed into conveyor style ovens. Food is seared from above and below as it passes by the hot air jets on a conveyor belt. Food items may sit directly on the conveyor belt or be placed on a pan or sizzle platter. The speed of the conveyor determines the total cooking time.
Impinger style conveyor ovens can cook a pizza four times faster than a traditional deck oven, and although they are a natural choice for takeout pizza operations, other possible applications include hot toasted sandwiches, nachos, breadsticks, cookies, seared seafood such as salmon and scallops, ribs, and more. Decks are stackable and available in a wide variety of sizes. A Kitchen Spot Expert can help you decide whether an impinger conveyor oven from manufacturers such as Lincoln are a good choice for you. Some manufacturers, such as MerryChef, have also incorporated impinger technology into their countertop speed ovens.
Hot air convection cooking increases cooking speed, improves browning, and promotes more even heating. Steam convection cooking increases cooking speed, helps food retain moisture, and improves yields. Used together, or in conjunction with other heating methods, convection cooking can dramatically change the way a classic commercial kitchen operates saving time, space, energy, and money, while improving food quality. Contact a Kitchen Spot Expert to learn more about convection cooking and the vast array of convection cooking equipment available.