This is the most common piece of equipment found in kitchens. It consists of either one or two ovens standing on short legs with a boiling table on top and a space between the boiling table and the oven top to allow for plate and dish heating and for grilling. The external dimensions of a double oven range are approximately 6 x 3′ X 3′, the capacity of each oven either 5 cu. ft. or 71 cu. ft. and the time for the temperature of an empty oven to rise 350°F. above room temperature is approximately 30 minutes. Naturally individual variations in size occur according to the designs of the various manufacturers, but these differences are not great. It will be noticed that the oven in the normal range is too low to conform to the ideal conditions described above. This position for the oven is clearly unavoidable in a model with a griller and boiling plate on top, since it is essential that the height of the plate should not exceed 3′, otherwise difficulties in lifting pans and in using the boiling table will arise.
Another example of a double oven range is illustrated in Plate II. In this model the boiling table heated by gas and called the ‘Solid Top’ provides a continuous area of metal heated by means of specially designed burners at various points. By this method temperature variations are obtained at will over the surface, a great convenience when it has to accommodate a large number of pans requiring a range of cooking conditions from fast boiling to simmering.
The General Purpose Oven
One arrangement is for two ovens to be joined together and raised on stands, and the other for them to be placed one above the other. The first arrangement as illustrated gives ovens at a very convenient height for use; the advantage of the second arrangement lies in the small floor area required to accommodate the two ovens. The external dimensions of each single oven are 38″ x 34″ x 30″ for gas and 42″ x 32″ x 34″ for electricity, and capacity 7 cu. ft. The time for the temperature of an empty oven to rise 350°F. above room temperature is approximately 30 minutes.
Cabinet Type Roasting Oven
This oven is designed primarily for the cooking of meat. It is fitted with shelves widely spaced to allow for the roasting of joints and also with rails at the top of the oven from which joints can if required be suspended for roasting. The external dimensions are usually 46″ x 70 x 4′ 6″ with an internal capacity of 12-15 cu. ft. The time taken for the temperature of an empty oven to rise 350°F. above room temperature is approximately 45 minutes.
Ovens of this type have obvious advantages where many large joints are to be cooked at the same time. Their disadvantages lie in the operational difficulties of the shelves at the top of the oven and in the high fuel consumption it c re is not exercised. The doors are very large so that if they are left open for more than the minimum amount of time necessary, considerable heat loss will result.
The Pastry Oven
This oven is designed for baking only and for reasons explained earlier in this chapter it has a narrow clearance of approximately 9″ between floor and top. The pastry oven illustrated in Plate V consists of three separate compartments and the external dimensions are 56″ x 66″ x 47″. One cannot generalize about dimensions of ovens of this type, as wide variations occur to meet specialized demands. Thus the compartment type of oven may have anything from one to six sections with widths varying from 2′ to 5′ and depths from 2’6″ to 4′ 6″.
The Baker’s Oven
Although this very large oven used in commercial bakeries is very rarely found in kitchens designed for catering only, it is interesting to consider it briefly here. The total baking area, which is all on one level, may be anything up to 100 sq. ft.; an oven for bread baking only may be even bigger and so constructed that the loaves pass continuously through it during the cooking process. The production of an even heat throughout with the requisite amount of top and bottom heat is a specialized subject which does not concern us here. There are however two special features connected with baking oven engineering which deserve consideration.
The Biker’s Steam Oven
This oven is designed entirely for the baking of French bread ind rolls with crisp crusts. To obtain this finish, the dough when placed in the oven must first of all be exposed to an atmosphere of steam which cooks it on the outside, leaving it soft and moist. The process is completed by releasing the stem and allowing the bread to cook in a dry atmosphere which gives it a crisp brown exterior.
Baker’s Oven Heated by Steam Pipes
This oven is of interest because the method of heating is of a somewhat unusual and specialized type. It is well known that if water is heated in a sealed tube, temperatures well above the boiling point of water can be obtained owing to the high pressure exerted by water vapor in an enclosed space. This principle is made use of to supply heat in one type of baker’s oven. Sealed tubes of 14″ diameter partially filled with water and tested to withstand pressures up to 750 lbs. per sq. in., are fitted in parallel rows in the ceiling and floor of an oven. One end of each tube is extended for some distance away from the oven and projects a few inches into the furnace. The temperature reached by these tubes is as much as 500°F. and they are a very efficient source of radiant heat.
Forced Convection Oven
The design of this oven is such that not only are total cooking times considerably reduced for all types of foods, but the output per cu. ft. is increased compared with ovens of the conventional type. With the aid of an electric fan hot air is constantly drawn across the food and all the shelves in the oven receive heat at the same rate.
The heating elements whether gas or electric are located in the two side walls of the oven between the insulated outer casing and a perforated or slotted panel. In the gas type the heat exchange elements, of about 50,000 B.T.U. capacity, consist of a series of metal tubes of 1″ diameter each mounted vertically above a gas combustion chamber. In the electric type the elements are of the sheath type with a total loading in the region of 12 Kw The electric fan is located in the center of the back panel (Plate XXIII) and sucks air out of the oven chamber and into the cavity between the linings of the insulated casing and the oven wall and in so doing draws air over the heating elements and through the slotted or perforated wall panels. This air circulation is mainly in a horizontal plane. The cavity into which the fan draws air has an opening to the outside air so that steam and hot air can be released. In the cooking of some foods a moist atmosphere is required, and in others a dry one. The oven is provided with a control to cover these contingencies.
Rotary or Reel Oven
In this type of oven (Plate XXIV) the trays of food are in continuous movement thus ensuring even cooking. Another advantage is the ease of loading because, as explained below, the oven shelves can be stopped and made to be available for loading at a convenient height.
The oven consists essentially of a large insulated heated box in which shelves are suspended on horizontal bars connecting two cylindrical rotating spiders. The spider is a disc which rotates in its own plane about the center, having a number of projecting spindles, usually six, from each of which shelves or other objects may be suspended. The shelves are usually 18″ in depth and may be up to 20′ or more in width. Each tray is numbered and its position in the oven is shown on an indicator, so that it is possible to stop the revolving mechanism when the desired shelf is opposite the door. The door is arranged so that the shelf is at a convenient height for loading. In many arrangements trolleys carrying the food to be cooked are at the same height thus eliminating lifting. In ovens of this type a total roasting load of up to 1,500 lb. can be cooked at one time.
In another smaller oven with square shelves of approximately 18″ x 18″ there is only one spider and the shelves rotate around it, rather like the chairs on the giant wheel at an amusement park.
The Lasmec Oven
This is an oven of the traditional type, rather like the pastry oven already described but shallower in depth. The word Lasmec is derived from the initials of Local Authority School Meals Equipment Consortium, who have developed a range of equipment on 2 modular unit of 36″ x 26″, particularly with a view to improving the efficiency of apparatus for school meals. This equipment has also been found useful in residential establishments. All drains, water and fuel services are contained in floor ducts within the area of the equipment thus giving an improved appearance, reducing floor area requirements and making cleaning easier. Installation costs are also reduced.
The internal dimensions of the oven are 24″ x 19″ x 10″ and it carries one shelf giving a clearance of 41″. The oven, which is mounted on a plinth, can be stacked in tiers of one, two or three, Och of which will accommodate four baking pans of 22″ x 8″ or roast 20 lb. of meat in 5/6 lb. joints.
The gas oven is heated externally by flue gases which circulate around the oven from a burner beneath the base plate. The electric oven has tubular sheathed elements in the back and sides and both ovens are designed to give good heat distribution, reduced cooking times and more even cooking, compared with the older types of ovens, thus eliminating the necessity to re-position while baking.
The finish of the exterior of the ovens is dull stainless steel, the lining of the back and sides is polished stainless steel, with top and bottom plates in cast aluminium. The lining of the oven door is of vitreous enamel with an inner panel of stainless steel.
The Microwave Oven
In this oven the food is neither roasted nor baked. It is cooked by the effects of high frequency radiation waves which penetrate the food to a depth of 41″, causing the food molecules to vibrate, and thus generating heat. With this oven it is necessary to use for the food a covered container made of a material such as glass or plastic which permits the transmission of the radiation waves and is not therefore heated by them. The lining of the oven also remains cold and because of this the external surface of the food which is constantly losing heat by radiation to these cold surfaces cooks more slowly than the interior.
Radiation waves in the 2450 m/c band are generated by a magnetron with a power loading of 21 Kw. which beams the energy into the food. A slowly moving fan within the oven stirs up the waves by reflecting them in different directions and thus increases evenness of distribution.
An important feature of this oven is its speed of cooking–for example a trout can be cooked in three minutes and an apple in four minutes. Another feature is the retention of the flavor of the food because during the short cooking time less of the volatile substances which contribute to taste are able to escape.
Although this oven can be used very satisfactorily for cooking food from raw, it is used most frequently for reheating cooked food either from the frozen state or after it has been tempered in a refrigerator to 40°F.
In this oven food is cooked entirely by radiation by waves generated in the infra red band at wave lengths between 7,000. Å and 20,000 Å. The quartz tubes of 1.1 Kw. loading have a single coil tungsten filament between molybdenum electrodes in a gas filed chamber. A feature of this oven is the initial speed at which the high intensity radiation is generated. Within two minutes of switching on the oven is ready for use.
Heat Conducting Pins
This device is designed to conduct heat into the inner parts of a piece of meat and thus cut down cooking times. It consists of a hollow stainless steel tube with a pointed tip and a finned black anodized aluminium head. Within the tube sealed to withstand a pressure of a few pounds, is a small quantity of water which when heated vaporizes and exerts a pressure thus raising the temperature within. For efficient operation the pin must be inserted so that the tip is higher than the head (Plate XXV).
The pins which are made in different lengths of up to 18″ to 20″ will reduce cooking times by as much as half, and can also be used for quicker boiling. Yet another use is to increase the rate of chilling or freezing of food in a refrigerator or deep freeze. When used for this purpose the tip must be lower than the head.