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Ovens

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Oven cooking is as ancient as civilization, as old as the baking of bread. Today, oven cooking is the most common food preparation method, and ovens are one of the most widely used kitchen appliances. Even the smallest establishment usually has a microwave to heat appetizers or sandwiches, and large facilities may have a conveyorized bake oven for high volume production.

Ovens are available in numerous sizes and designs. Some are designed for specialized food preparation tasks, while others are meant for a range of cooking applications. One recent design, called a Flash Bake oven, uses a combination of high intensity visible light and radiant heat to increase production speed and improve food preparation quality. There are also many "cook and hold" ovens that improve preparation consistency and product quality and cook foods at lower temperatures to increase nutritional value and reduce energy consumption.

Ovens are often the largest consumers of energy in a food service kitchen. Oven design and construction quality, as well as fuel type, affect the amount of energy lost to the kitchen as heat. In typical electric ovens, only 40 to 60% of the source energy is used to cook; in gas ovens, this is only 10 to 30%. The remaining source energy escapes into the kitchen, making staff uncomfortable and adding to cooling costs.

Some newer oven technologies increase speed and energy efficiency and reduce food-portion weight loss, making oven operation more economical. These improvements usually involve greater initial cost, but may actually reduce overall costs over time.

Oven types

There are a wide range of oven types. The most common types are described below.

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All-purpose ovens

All purpose ovens are used for baking, roasting, cooking pizza, and many other combined cooking tasks. Each section of an all-purpose oven adapts easily to a modular lineup.

All-purpose oven production capacity varies by model. Independent controls and heating element banks are usually located at either the top or bottom of the oven unit. These let operators perform special tasks, such as custom browning, with balanced or unbalanced heat.

Some standard oven decks are air cushioned to improve heat diffusion. Others have a removable core-plate that optimizes heat diffusion and holding.

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Convection ovens

Convection ovens circulate air in the oven cavity using a fan. This air movement speeds cooking by increasing heat transfer to the food. Convection ovens are ideal for low-temperature slow roasting, and many feature a slow "cook and hold" setting. Slow roasting meats at low temperature reduces shrinkage (and thus food costs) and tends to produce food of higher quality. Electric convection ovens are often preferred because they have smaller losses in oven humidity during cooking.

The air flow through the oven chamber allows convection ovens to cook large loads and multiple racks effectively. Modern units have oven chambers insulated on all six-sides, providing peak energy efficiency. Solid state thermostats precisely control temperature, with cooking times digitally displayed for easy monitoring.

Most electric convection ovens preheat to a typical operating temperature of 350°F within six to ten minutes. Comparable gas ovens are generally slightly slower coming to temperature. Both types offer optional non-stick or stainless steel liner panels that are removable for speedy cleanup.

An optional heat-keeper recirculation system can save energy costs with gas convection ovens by re-using heated air that would normally be wasted. In these gas models, a power burner is provided for maximum energy efficiency.

Convection ovens are not ideal for every oven application. They tend to dry products out during cooking, which may deteriorate food quality, especially with pastries. In these cases, a traditional oven is better.

Half-size convection ovens

Half-size convection ovens are a good choice when a full size oven for a given commercial cooking application would result in significant energy losses. In these cases, the smaller size of the half-size oven reduces losses while still meeting food production requirements.

Combination ovens

A combination oven combines the features of a convection oven and an atmospheric steamer. These ovens use the combination of oven and steamer cooking methods to maximize quality and speed. Steam injection is especially desirable in producing high-quality, golden-brown, crusty breads. Quality is further enhanced by the forced air distribution.

This multipurpose oven offers a variety of cooking methods:

  • Hot air convection (some with water injection for high moisture)
  • Convection steam
  • A combination of convection, steam, and hot air circulation, and a cook-and-hold feature

Enclosed tubular convection heating elements produce heat that circulates by a small blower motor. Most units have an extra large observation window to monitor cooking and a timer to track cooking time. Time and temperature controls with digital displays help operators track the cooking process. Some units also offer memory programming for multiple recipes with cooking cycles. The steam boiler can be heated electrically or by gas.

A roll-in floor model combination oven and steamer has a cooking capacity of dozens of cafeteria pans and bun pans.

Proofing ovens

Many breads and pastries require a high humidity environment for optimal yeast action and product baking. To meet this need, special ovens exist with enhanced humidity control for the "proofing" stage in baking. These ovens can also be used to hold cooked food for extended periods of time.

Most holding ovens surround food with hot air to keep it warm. This causes moisture to evaporate, which shrinks food, reduces visual appeal, and deteriorates flavors, texture, and consistency. However, food will not release moisture and dry out if the air around it is kept saturated. Most proofing ovens have been perfected to the point that they can keep some foods moist and others crisp in the same oven enclosure.

Steam injection ovens

Steam injection ovens are essentially standard convection ovens that can produce and inject steam. This steam injection desirable in producing high-quality, golden-brown, crusty breads. Quality is further enhanced by the forced air distribution.

Electric rotary ovens

Electric rotary ovens are ideal for supermarkets, delis, and convenience stores. Large glass doors help build purchase-point interest by allowing the product to be viewed during cooking.

These ovens cook with a combination of convection and radiant heat and often incorporate an air circulation system that allows the unit to act as a warmer. This system maintains high humidity to keep the food contents juicy. In addition, the self-basting cooking action of these units enhances browning .

Electric rotary ovens are equipped with digital timers and controls simplifying operation. They also usually come with multiple racks. The large removable trays and racks are easy to clean, which reduces labor costs.

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Microwave ovens

Microwave ovens cook by heating water and chemical molecules in food with short-wave radio energy like that used in radar and television. The frequency most commonly used in the microwave oven is 2,450 megahertz. Microwave ovens consume the least amount of energy and are highly space efficient.

One microwave oven advantage is quick de-frosting, heating, and cooking of foods. The ability to defrost and warm foods in a matter of seconds makes these units popular with food service facilities wanting high menu variety for a large volume of customers. These establishments often pre-cook foods and refrigerate them until peak serving periods and then quickly heat portions during peak time periods.

A disadvantage of the microwave, however, is it cooks foods from the inside out, as opposed to outside in as with most cooking systems. This typically does not provide the surface browning desired in many cooking applications. This can be solved by transferring the food to another type of oven for final browning.

Cooking capabilities differ only minimally among different microwave oven models. Microwave ovens are available in an array of sizes and with a number of features. Top and bottom, or bottom-only energy feeding systems are available. Each type has rotating wave guides to minimize "hot spots" common to residential style units.

Flash bake ovens

A Flash Bake oven uses a combination of intense visible light and infrared energy to cook food rapidly. The visible light penetrates the food to provide heating while the infrared energy cooks the food surface to achieve the desired browning. Microprocessor control makes these units flexible and intelligent in their operation, and can produce superior quality for fish, meat, vegetables, breads, and many other types of foods.

The primary benefits of Flash Bake technology are its speed and energy efficiency. The shortened cooking time also has the advantage of producing more nutritious and better tasting food. The Flash Bake oven was designed to cook relatively flat, thin foods. Pizza, nachos, quesadillas, and other foods with similar geometry are ideal for this technology.

The primary disadvantage is one of perception: the oven simply appears to be too small to be a serious food preparation device. However, the unit's high speed and excellent performance have been proven in many establishments. These establishments have found the unit highly cost effective. Perceptions should change as the benefits of this oven are demonstrated to commercial food service professionals.

Another disadvantage of the Flash Bake is that the increased heat transfer rate must be balanced against possible surface overheating. This can be minimized by operator training and advanced computer controls.

New oven technologies

Gas and electric oven manufacturers continually improve oven insulation and controls, heat transfer effectiveness, and heat recovery. These improvements yield higher efficiency and shorter preheat times. Many newer designs also maintain a more uniform temperature in the oven zones.

For example, conduction ovens circulate a heat transfer fluid through plates to provide more accurate and uniform heating. Also, Flash Bake technology is especially effective in the preparing trendy foods, such as quesadillas and pizzas.

Comparing electric vs. gas ovens

There are many factors to consider when selecting an oven: initial cost, food preparation productivity, ease of operation, heat generation in the kitchen, and whether electricity or gas is used as the energy source. However, consider that energy only accounts for 3 to 5 percent of a typical food service establishment's total costs. Therefore, while one fuel may be less expensive in a BTU to BTU comparison, the best choice in cooking equipment is the one that minimizes total operating costs, not just energy costs. Features that reduce labor costs or result in higher food product yield will nearly always outweigh any energy considerations. Make sure that you include all of these factors in any equipment evaluation.

Therefore, when comparing gas an electric models, compare equipment that is similar in all ways except the energy source.

Advantages of electric ovens

In general, electric ovens offers these advantages:

  • Electric units are more efficient, adding less heat to the kitchen that must be removed by the kitchen cooling system.
  • Electric units require less maintenance, require less ventilation, and are more portable.
  • Electric ovens, especially those with electronic controls, deliver more consistent run quality and require less operator supervision. They are also considered to be cleaner and more flexible (especially where maintaining oven humidity levels is important). Kitchen design and modification may also be simplified because venting may be unnecessary.

Energy and money saving tips

  • Here are a few common-sense operating tips that save money with a oven.
  • The efficiency of ovens depends upon how well they are constructed, and insulation levels and quality are significant factors. Consider this in purchasing decisions, since some inexpensive ovens have little-to-no insulation in the oven door and will cost more to operate.
  • Ovens consume considerable energy when left on, even if no food is being cooked. Energy is lost through the oven walls and leakage around the door opening. These losses can be a significant operating expense, so turn all oven equipment off or lower temperatures during non-operating intervals. This saves energy, reduces cost, and increases oven life.
  • When a food service production does not call for a full sized oven, consider a half-size oven that may operate at much lower cost.

Oven components

An oven is composed of a box-like enclosure, heating elements, and controls. The enclosure ranges from a counter-top size to larger free-standing and floor model units. Ovens usually have a hinged door at the front or side (conveyer ovens have openings on two sides), and include adjustable racks or trays to hold food . The quality and amount of insulation and presence of an air curtain (to retain oven heat when the door is opened) all affect energy efficiency and uniformity of heating.

In standard electric ovens, electric heating elements may be at the top, bottom, or sides of the oven. Gas units use gas combustion chambers. Microwave designs provide heating energy by channeling electromagnetic waves into the oven and rotating the food items to assure uniform heating. Flash Bake ovens use a combination of high intensity light plus infrared radiant energy for extremely rapid heating. In some special oven designs, steam is used to shorten cooking times and improve certain food preparation. Yeast-raised breads and pastries are often baked in humidity-controlled proofing ovens.

Deck ovens and conveyer ovens use convection as a heat transfer medium, but are named for the special large heated deck on which food is placed during cooking. These are commonly used for roasting, baking, and cooking pizza.

Oven controls indicate desired oven temperature. Certain designs also provide "cook and hold" cycles that extend holding time and improve the quality of food.

Oven operation tips and issues

Since ovens are so common, most people are familiar with their operation. The oven is first preheated to the desired cooking temperature. Next, food to be cooked in the oven is usually placed in containers of metal or glass or on metal pans. The food is then heated at a specified temperature for a certain period of time. The time required depends on the size and shape of the food items heated and the rate of acceptable heat transfer to those items. For example, thin items like pizza heat much rapidly than large items like whole turkeys, and a stuffed turkey takes significantly longer to cook than an unstuffed turkey.

Some foods require changes in oven temperature during cooking, especially where surface browning is desired. For example, a recipe may require extended initial baking at 325°F, and the last few minutes at 425°F.

The most common oven-cooking process surrounds the item being cooked in hot air. However, air is a relatively poor heat transfer agent, especially compared to the heat transferred by a griddle or immersion in hot oil. The air heat-transfer can be accelerated by circulating or blowing the hot air around the food being cooked.

Apart from air, some oven designs use high intensity and infrared light, microwave energy, or steam. Each design has a special niche in the preparation of foods. No one oven design is ideal for all food preparation, so many modern ovens incorporate a combination of these technologies.

For more information about the benefits of electric convection ovens vs. gas, please contact us for a copy of an EPRI performance report.