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Monday, May 23, 2011

Homemade Fireless Cookers

Original Article

[Adapted from the USDA Farmers Bulletin #771]

The principle employed in the fireless cooker has long been known and may be briefly stated as follows: If a hot body is protected by a suitable covering the heat in it will be retained for a long time instead of being dissipated by radiation or conduction. In using a fireless cooker the food is first heated on the stove until the cooking has begun and then it is placed in the fireless cooker, a tight receptacle in which the food is completely surrounded by some insulating substance, which prevents the rapid escape of the heat so that it is retained in the food in sufficient quantity to complete the cooking. Sometimes an additional source of heat, such as a hot soapstone, or brick is put into the cooker with the food where a higher cooking temperature is desired. The same principle is also employed in other ways in cookery. For example, in camps, beans are often baked by burying the pots overnight with hot stones and ashes, the whole being covered with earth, and in the “clam bakes” on the Atlantic coast, the damp seaweed spread over the embers and the clams prevents the escape of the heat during cooking. The peasants in some parts of Europe were said to have started their dinner cooking and then put it into hay boxes or between feather beds so that the cooking may be completed while the family is absent in the fields.
One of the chief advantages of the fireless cooker is that it accomplishes a saving in fuel, especially where gas, kerosene, or electric stoves are used. Where coal or wood is the fuel, the fire in the range is often kept up most of the day and the saving of fuel is less. In summer or when the kitchen fire is not needed for heating purposes, the dinner can be started on the stove early in the morning and then placed in the fireless cooker, the fire in the range being allowed to go out. During hot weather the use of a kerosene or other liquid fuel stove and a fireless cooker is a great convenience, since it not only accomplishes a saving in fuel but helps to keep the kitchen cooler. As would be expected, the saving in fuel resulting from the use of a fireless cooker is greatest in the preparation of foods like stews, which require long and slow cooking.
The great convenience of the fireless cooker is that it saves time, for foods cooked in it do not require watching and may be left to themselves while the cook is occupied with other duties, or the family is away from home, without danger from fires or overcooking the food. Its use, therefore, may enable a family to have home cooking instead of boarding, or hot meals instead of cold foods. Another advantage of the use of the fireless cooker is that it makes it easier to utilize cheaper cuts of meat, which, although not having as fine a texture or flavor, are fully as nutritious, pound for pound, as the more expensive cuts. Long cooking at relatively low temperature, such as is given foods in the fireless cooker, improves the texture and flavor of these tougher cuts of meat.

While there are many good fireless cookers on the market, it is possible to construct a homemade cooker which, if properly built, will give very satisfactory results and is cheaper than one which is purchased. The materials needed are a box or some other outside container, some good insulating or packing material, a kettle for holding the food, a container for the kettle or a lining for the nest in which the kettle is to be placed, and a cushion or pad of insulating material to cover the top of the kettle.
For the outside container a tightly built wooden box, such as that shown in figure 1. is probably the most satisfactory. An old trunk, a small barrel, or a large butter or lard firkin or tin may be used. Another possibility is a galvanized-iron bucket with a closely fitting cover; this latter has the advantage of being fireproof. A shoe box 15 by 15 by 28 inches is convenient in size, since it may be divided into two compartments. The box should have a hinged cover, and at the front side a hook and staple or some other device to hold the cover down; an ordinary clamp window fastener answers the latter purpose very well. Whatever the container used, its size, which depends upon the size of the kettle used, should be large enough to allow for at least 4 inches of packing material all around the nest in which the kettle is placed.
Fig. 1.—Homemade fireless cooker, showing outside container and cushion for filling space above the cooking vessel.

The kettles used for cooking should be durable and free from seams or crevices, which are hard to clean. They should have perpendicular sides and the covers should be as flat as possible and provided with a deep rim shutting well down into the kettle to retain the steam. (See fig. 2.) It is possible to buy kettles made especially for use in fireless cookers; these are provided with covers which can be clamped on tightly. The size of the kettle should be determined by the quantity of food to be cooked. Small amounts of food ca not be cooked satisfactorily in large kettles, and it is therefore an advantage to have a cooker with compartments of two or more different sizes. Kettles holding about 6 quarts are of convenient sizefor general use, Tinned iron kettles should not be used in a fireless cooker, for, although cheap, they are very apt to rust from the confined moisture. Enameled ware kettles are satisfactory, especially if the covers are of the same material. Aluminum vessels may be purchased in shapes which make them especially well adapted for use in fireless cookers and, like enameled ware, they do not rust.
Fireless cookers are adapted to a much wider range of cooking if they are provided with an extra source of heat, since a higher cooking temperature nun’ thus be obtained than if hot water is depended upon as the sole source of heat. Obviously this introduces a possible danger from fire in case the hot stone or other substance should come into direct contact with inflammable packing material like excelsior or paper. To avoid this danger a metal lining must be provided for the nest in which the cooking vessel and stone are to be put. As an extra source of heat a piece of soapstone, brick, or an iron plate, such as a stove lid, may be used. This is heated and placed in the nest under the cooking vessel; sometimes an additional stone is put over the cooking vessel.

Fig. 2-Cover provided with deep rim shutting down into the kettle to retain the steam.
The container for the cooking vessel, or the lining for the nest in which it is to be put, should be cylindrical in shape; should be deep enough to hold the cooking kettle and stone, if one is used; and should fit as snugly as possible to the cooking vessel, but at the same time should allow the latter to be moved in and out freely. If the cylinder is too large the air space between it and the kettle will tend to cool the food. For this purpose a galvanized iron or other metal bucket may be used or, better still, a tinsmith can make a lining of galvanized iron or zinc which can be provided with a rim to cover the packing material (as shown in fig. 3). In case no hot stone or plate is to be used in the cooker, the lining can be made of strong cardboard.

Fig 3.—Metal lining for nest of fireless cooker: A, Rim to cover packing material. B, Metal container for cooking kettle and hot stone.

For the packing and insulating material, a variety of substances may be used. Asbestos and mineral wool are undoubtedly the best, and have the additional advantage that they do not burn. Ground cork, hay, excelsior, Spanish moss, wool, and crumpled paper may also be used satisfactorily. Of the inexpensive materials that can be obtained easily, crumpled paper is probably the most satisfactory, since it is clean and odorless and, if properly packed, will hold the heat better than some of the others. To pack the container with paper, crush single sheets of newspaper between the hands. Pack a layer at least 4 inches deep over the bottom of the outside container, tramping it in or pounding it in with a heavy stick of wood. Stand the container for the cooking vessel, or the lining for the nest, in the center of this layer and pack more crushed papers about it as solidly as possible. The method of packing with paper is illustrated in figure 4. If other packing, such as excelsior, hay, or cork dust, is used, it should be packed in a similar way. Where an extra source of heat is to be used, it is much safer to pack the fireless cooker with some noninflammable material, such as asbestos or mineral wood. A cheap and easily obtained substitute are the small cinders sifted from coal ashes, preferably those from soft coal, which may be obtained at the boiler house of any mill. The cinders from hard coal burned in the kitchen range will do, however. Experiments with this material made in this office showed that it is very nearly as satisfactory as crumpled paper as a packing material. If a fireproof packing material is not used a heavy pad of asbestos paper should be put at the bottom of the metal nest and a sheet or two of asbestos paper should be placed between the lining of the nest and the packing material. Whatever packing material is used, it should come to the top of the container for the kettle, and the box should lack about 4 inches of being full. A cushion or pad must be provided to fill completely the space between the top of the packing and the cover of the box after the hot kettles are put in place. (See fig. 1,) This should be made of some heavy goods, such as denim, and stuffed with cotton, crumpled paper, or excelsior. Hay may be used, but will be found more or less odorous. Figure 5 shows the vertical cross section of a homemade fireless cooker.

Obviously the fireless cooker must be to obtain the best results. It is best which require boiling, steaming, or long, slow cooking in a moist heat. Foods cannot be fried in it, pies cannot be baked successfully in the ordinary fireless cooker, nor can any cooking be done which requires a high, dry heat for browning. Meats, however, may be partially roasted in the oven and finished in the cooker, or may be begun in the cooker and finished in the oven with much the same results as if they were roasted in the oven entirely. The classes of food best adapted to the cooker are cereals, soups, meats, vegetables, dried fruits, steamed breads, and puddings.
When different foods are cooked together in the fireless cooker they must be such as require the same amount of cooking, since the cooker cannot be opened to take out food without allowing the escape of a large amount of heat and making it necessary to reheat the contents. It would not do to put foods which need about one and one-half hours to cook into the cooker with a piece of meat which would stay several hours.

Fig 5.—longitudinal section through tireless cooker, showing details of the construction: A, Outside container (wooden box, old trunk, etc.) B, Padding or Insulating material (crumpled paper, cinders, etc.). C, Metal lining of nest D, Cooking kettle E, Soapstone plate, or other source of heat, f, Pad of excelsior for covering top O, Hinged cover of outside container.

The size of the container used in cooking with the fireless cooker should be governed according to the amount of food to be cooked. Small quantities of food cannot be cooked satisfactorily in a large kettle in the fireless cooker. If a large kettle must be used better results will be obtained if some other material which holds heat fairly well is used to fill up the empty space. This may be accomplished in several ways. One is to put the small quantity of food to be cooked into a smaller, tightly closed kettle, fill the large kettle with boiling water and put the small kettle into it, standing it on an inverted bowl or some other suitable support. This boiling water will take up and hold the heat better than air would. Several smaller dishes (if tightly covered) may be placed in the kettle surrounded by boiling water. Baking powder or other tins often are found useful for this purpose. Another way is to place one food in a basin which just fits into the top of a large kettle and to let some other material, some vegetable perhaps, cook in the water in the bottom of the kettle. Two or more flat, shallow kettles placed one on top of the other so as to fill the cooker enable one to cook small amounts of different foods successfully. Such kettles, made especially for use in fireless cookers, may be purchased.
The time which each kind of food should stay in the cooker depends both on the nature of the food and on the temperature at which it remains inside the cooker, and before recipes for use with the fireless cooker can be prepared one must have some means of knowing how temperatures are preserved in it. In experiments made in this office a 6-quart kettle was filled with boiling water and put into the cooker, the packing of which happened to be newspaper. The temperature of the water, which was 212° F. when put into the cooker, was found to be 172° F. after four hours had elapsed and 155° F. after eight hours had elapsed. This shows the advisability of the common custom of allowing food to remain undisturbed in the cooker for at least six or eight hours, or in some cases overnight. If a soapstone, hot brick, or other extra source of heat is used, less time will be required. Materials which are denser than water (sugar syrup as used in cooking dried fruit), and therefore can be heated to a higher degree, will keep up the temperature longer when put into the cooker. Thus the density of the food material, as well as the amount and the length of time that the apparatus retains the heat, must be taken into consideration in determining how long different materials must be cooked in the cooker.
The recipes for dishes to be prepared in the fireless cooker differ somewhat from those for foods cooked in the ordinary way, chiefly in the amount of water or other liquids called for. Less liquid should be put into the food to be prepared in an ordinary fireless cooker, since there is no chance for water to evaporate. The cook must be guided largely by experience in deciding how long the food should be heated before being put into the cooker and how long it should be allowed to remain there.

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