oven
An oven is an electrically or fuel-heated device for baking, roasting and grilling food. It is used in the household, in the trade and in the industrial sector. In parts of Germany and Austria, the oven will be oven , and oven or only tube called.
Historical oven in Hermannsburg
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Typology
Basically, ovens can be differentiated according to the type of
- Heat transfer : heat radiation , convection ( circulating air )
- Heating : direct or indirect
- Heat transfer medium : air , flue gas , thermal oil , water
- Energy sources : gas , heating oil , wood (logs, wood chips , pellets ), coal , electricity
- as well as according to the design: wagon furnace, deck furnace, continuous furnace, reversing furnace
history
Clay oven
Construction
The foundation is formed by large field stones embedded in sand . The baking surface is made of bricks that are laid on a layer of sand. The arch of the baking chamber is made of bricks and clay ( oven clay ). The clay walls are made of mud bricks, a mixture of clay, straw and water. The furnace walls are 0.30 m thick in most places. Height of the furnace inside 0.80 m, outside 1.10 m. Most of the time, the ovens did not have a chimney , but only a hole in the back of the oven for the smoke to be extracted. The stove was protected by a large roof.
Heat
In the clay oven half is about cubic meters of split meters of wood layered. The burn takes about 6 hours. The bakehouse is heated from the back to the front, so the logs are lit in the front room and then pushed backwards. Little by little the logs are now placed on the fire and pulled forward again. Then the embers are properly distributed in the oven. After 1 to 1.5 hours, the embers are removed from the oven. A wet jute sack is then wrapped around the embers and the oven floor is wiped out with it until it is clean (“ baker's flag ”). After the remaining embers have been removed, the walls radiate the stored heat onto the baked goods. Ears of rye were placed in the oven to control the temperature . If they burned, the stove was too hot and had to be brought to the right temperature (approx. 240 ° Celsius) with a wet sack. However, if the ears of corn turned nice and brown, the temperature was just right and the bread dough could be pushed in.
to bake
Most of the time a “pre-cake” was baked beforehand. Then the actual cake came in, which was done in five to seven minutes. Different types of cake were baked: butter cake , apple cake , and the Luffen, a kind of mares . Then immediately put 20 to 40 loaves of bread into the oven. These had to stay in the oven for about an hour. The bread consisted of mixed grain ( wheat and rye ), sourdough , salt and lukewarm water. Depending on the type of wood with which the bakery was heated, the bread had a soft or hard crust. Usually beech wood was used for heating. B. willow wood for heating, the bread got a softer crust. In autumn, after bread was baked, fruit ( apples , pears and plums ) were often dried in the still warm oven .
The term "push" means "shoot" or "shoot in" for bakers. This is done with the back shooter.
Fireplaces and thus also ovens were often the starting point for causes of fire in the 18th century. Orders from Count Palatine Karl IV. From 1772 served to prevent a fire in connection with fireplaces. So no more wooden chimneys were allowed to be built, no more wooden hoses were allowed to be installed, which had to lead the smoke from the fireplace to the fireplace, as it was also forbidden to lead stove pipes out of the window.
Modern craft ovens
Modern ovens are characterized by their baking chamber, in which the thermal energy is transferred to the baked goods through thermal radiation, convection and / or thermal conduction. During baking, part of the dough water evaporates, the dough piece loses part of its mass on the way to the finished baked product (so-called baking loss). An essential component of a modern oven is the steam device, which generates steam when water is added, which can be introduced into the baking chamber at the beginning of the baking process. This steam can condense on the still cold surface of the dough and keeps it flexible for a short period of time, so that a corresponding volume can develop due to the oven impulse that starts at the same time without the surface tearing open unintentionally. The steam also serves to create a shiny surface for the baked goods. Bakeries in France and Italy usually work with little, delayed or no steam at all, the corresponding baked goods such. B. baguette or ciabatta (also because of any durum wheat flours used) are crispy and have a rustic look.
The group of modern craft ovens can be divided in rack ovens , deck ovens and baking ovens .
Rack ovens
Rack ovens fall under the category of wagon ovens. Baking trays with dough pieces are pushed into a trolley (rack) running on rollers so that the rack oven can be loaded and unloaded in one operation. Rack ovens work on the principle of convection, i. that is, it is baked with hot air. For this purpose, the baking chamber air is sucked in by means of a fan, passed through a heat exchanger (with a large surface) and heated. The heated air is returned to the baking chamber via adjustable nozzles and flows through the rack trolley with the baking trays. Some of the energy from the hot air is transferred to the dough pieces, which are then baked. The air is then heated again. To achieve better uniformity, the rack trolley can rotate around its vertical axis; it is either driven onto a turntable or picked up by an overhead rotating hook. The heating can be done by gas or oil burners as well as by electrical heating resistors. An essential component is a sufficiently dimensioned steam device (steam generator), the heated thermal mass of which can be sprayed with water in order to generate steam when baking starts. Also of great importance is the venting, which removes the steam generated during baking and supplies "dry" fresh air if necessary. The baking temperature, the baking time, the amount of steam and the steam removal can be controlled via the oven control. Nowadays the control is mostly electronic with the possibility of saving baking programs in order to bake fully automatically without the baker having to intervene during baking. The rack oven is primarily used for small baked goods. The main advantages are the simple and quick loading and unloading as well as the relatively large baking area in relation to the installation area. The disadvantage is that when baking begins, the dough pieces sit on baking trays that are still cold, so that the bottom of the dough pieces is not baked as well as there is no bottom heat.
Deck ovens
The deck oven is the classic artisanal oven for making bread, which can be seen as the successor to the wood oven. It consists of several baking chambers lying one on top of the other with openings for loading that can be closed through the baking chamber door and hotplates, usually made of natural or artificial stone, for receiving the baked goods. The heat is mainly transferred to the baked good by radiation (all around) and additionally by heat conduction (from below). For this purpose, the baking chamber is heated from above as well as from below either directly (e.g. by means of electrical heating resistors) or indirectly via a heat transfer medium (e.g. flue gas, water / steam, thermal oil). Each baking chamber has its own steam device (see rack oven), which is also heated by the heat transfer medium, as well as its own venting device (steam slide). In the case of the electrically heated deck oven, the baking temperature in each baking chamber can be controlled separately via the upper and lower heat. In the case of the indirectly heated deck ovens, all baking chambers normally have the same temperature, but baking chambers can also be combined into groups through separate channels of the heat transfer medium, which then each have their own and conditionally controllable temperature. Electronic controls are also becoming more and more popular with deck ovens, even if the use of baking programs is only possible to a limited extent due to the uniform temperature for the baking chambers and only the baking time, steaming and steaming can be controlled in relation to the baking chamber. The ovens can be loaded using a cloth puller (shooter) for baked goods that have been pushed out or using baking trays. This is relatively complex and is increasingly supported by loading aids (semi or fully automatic). There is also the option of using so-called pull-outs, in which the entire baking surface can be pulled out and thus loaded and unloaded.
Shop ovens
In order to be able to offer constantly fresh baked products, more and more in-store baking ovens are used in bakery branches, which, depending on the dough pieces used (fresh, uncooked frozen, cooked frozen, proofing retarded or half-baked), range from simple warming devices to full-fledged ovens with hot air or deck ovens Use. It is loaded with baking trays. The controls are fully programmable, but easy to use, as the ovens are usually not operated by a trained baker, but by sales staff.
Industrial ovens
Due to the cost pressure, attempts are also being made in the baking industry to reduce manufacturing costs. Since material costs can only be reduced through increased purchase quantities without lowering the quality, the main approach is to reduce production costs through more and more automation (e.g. bread roll lines ). The tunnel ovens, single-hearth and very long deck ovens, which instead of the hotplate have a continuous or step-driven mesh belt on which the dough pieces move through the oven and are baked, have long been in use in the industrial sector. The baking time results from the length of the oven and the speed. Flue gas, thermal oil and water or steam are used as heat carriers. The steam usually comes from a separately heated steam generator. In order to avoid the imprints of the mesh belt on the underside of the bread, plate hinged belts or strip-shaped stone slabs can also be used. For reasons of space and to increase flexibility, multi-hearth continuous ovens were also developed. Here, before and after the oven, loaders and unloaders are required that move vertically and bring the dough pieces or the baked bread to and from the individual floors.
The production in bread factories is largely fully automated, apart from batch- wise dough production, the entire production process is continuous and works with assembly lines.
Household ovens
Almost every modern kitchen has an oven, the thermally insulated interior of which is usually heated with electricity or gas. Depending on the design, an oven can be operated in one or more ways.
Built-in ovens are standard 60 cm high and wide according to the European standard DIN EN 1116 "Coordination dimensions for kitchen furniture and appliances", ovens according to the Swiss SMS standard for under - mounting are designed for 55 cm recess width and with a slide-in drawer usually 76.2 cm high.
Heating methods
If the ceiling and floor of the interior are heated by heating coils , one speaks of top and bottom heat . If the top and bottom can be switched separately from each other, it is called top or bottom heat accordingly . The heat is transferred to the baked good from above and / or below by thermal radiation. In an oven with a grill , an uncovered heating coil mounted on the ceiling shines intensely on the interior in order to achieve an intensive browning of the grilled . With some devices, the air circulation mode can also be switched on in order to achieve faster cooking.
In the convection oven, the heated air is distributed faster and more evenly by a fan inside the oven. Several levels / baking trays can be used at the same time. Compared to ovens with conventional heating, the temperature can be set 20 ° C to 30 ° C lower, as the moving air makes the heat transfer more efficient.
A hot air oven having a circulating air oven as a fan, to which a ring heating element is mounted. The air is heated (the hot air) and circulated in the stove immediately after it leaves the fan. Even more even heat distribution can be achieved by periodically reversing the direction of rotation of the fan (e.g. every 1 or 2 minutes).
There are two technical variants:
- The heating element / heating coil and fan are inside the cooking space. Due to the high surface heat, it is only partially suitable for baking or casseroles.
- The heating element / heating coil and fan are outside the cooking space (greater installation depth, as they are attached to the rear of the appliance). This technical variant delivers the heat evenly into the cooking space.
Assembly
The oven is loaded from the front via a front door or a front drawer. Baking trays and grids are either traditionally attached to the inside of the oven in slide- in guides, pushed into the oven with telescopic rail guides or, when attached to the drawer, pushed into the oven with the entire baking trolley. In modern ovens, trays and grids are often equipped with telescopic rail guides and thus designed as telescopic pull-outs. The first oven with such a ball-bearing telescopic guide was developed by Neff under the name Clou 1987 / 1988 brought to market. If the oven is equipped with a baking trolley, the trays and grids are hooked into the front of the drawer and pushed into the oven with the entire drawer.
Self cleaning
Most of the newer oven models have a self-cleaning function called " pyrolysis ". This works exclusively through heat, which can be up to 600 ° C: The interior of the furnace is burned out, the dirt is carbonized so that it either falls off by itself or can be easily removed; this process is relatively energy-intensive . This ash can then be easily wiped off with a damp sponge (at the earliest after the cooking space has cooled down). Before pyrolytic self-cleaning , all telescopic runners in the oven must be removed, otherwise the fats and lubricants on the small ball bearings will also be burned off during cleaning.
This technique is also popular for cleaning cooking grids. When the grill fire has reached the highest heat, you place the grate over or directly in the fire for several minutes and then remove the dirt more easily.
Advantages and disadvantages of pyrolytic self-cleaning
advantages
- The better thermal insulation compared to conventional ovens means that less electricity is used. The relatively high energy consumption of the cleaning process is compensated for by better thermal insulation during normal operation.
- After the cleaning process, only ash remains, which can be easily removed with a damp cloth.
- The pyrolytic self-cleaning not only saves a lot of effort and time, it also saves the use of often expensive chemical oven sprays. Chemical agents for cleaning the oven are not necessary.
disadvantage
- Pyrolytic cleaning requires very high temperatures. The cleaning process is quite time-consuming at around three hours.
- Devices with a pyrolysis function are more expensive than those with a catalytic self-cleaning function.
Oven lamps
Oven lamps are special illuminants because they have to withstand temperatures of 300 ° C and more over the long term. In addition to the lamp base , voltage and power consumption, the temperature range and the size and shape of the glass body are more important than with other general-purpose incandescent lamps .
See also
literature
- Claudia Lorenz-Ladener: Wood ovens in the garden, building instructions for clay and stone ovens. Ökobuch-Verlag, Staufen 2011, ISBN 978-3-922964-69-8 .
Web links
Individual evidence
- ^ Franz-Josef Sehr : The fire extinguishing system in Obertiefenbach from earlier times . In: Yearbook for the Limburg-Weilburg district 1994 . The district committee of the Limburg-Weilburg district, Limburg-Weilburg 1993, p. 151-153 .