Pressure cooker
The pressure cooker , pressure cooker , pressure cooker , steam pressure cooker , pressure cooker is a cooking pot in which foods at higher temperatures than the Normalsiedetemperatur (for water 100 ° C at sea level ) cooked can be, thereby shortening the cooking time. The increase in the boiling point is made possible by the fact that increased pressure can build up in the pressure-tight closed pot.
Some brand names developed into a designation that is still common today for the pressure cooker, especially Kelomat in Austria and Duromatic in Switzerland.
history
In 1679 Denis Papin invented the Papin pot , with which the boiling temperature of water could be influenced by generating different pressures. This was also used in scientific laboratories.
A modern pressure cooker came on the market in 1927 under the brand name Sicomatic ( Siko for short for "safety cooking pot") from the Riedling company Silit . The Flexsil brand pressure cooker from Sigg in Frauenfeld became popular in Switzerland . Its pressure relief valve worked with a weight stone, not a spring. The flexible (and pretensioned curved) lid was clamped into the inwardly protruding edge of the pan without a rubber seal, whereby the lid handle served as a lever and was not closed with a bayonet lock as is common today. On May 18, 1946, Max Keller from Zurich submitted a patent application to the Swiss Institute for Intellectual Property for “insert bodies for pressure vessels, especially for pressure cookers, with a signal device and a pressure relief valve”. 1949 arrived in Switzerland Duromatic from Kuhn Rikon to the market. The Kelomat was developed in Austria in the 1950s .
Layout and function
construction
The pressure cooker is a thick-walled saucepan, the opening of which has an outwardly curved edge with bayonet-like recesses for the pressure-resistant mounting of the lid. The lid has a rubber ring seal and usually both a control valve and a safety valve to limit the pressure . Modern pressure cookers have valves firmly integrated into the lid, whereas older ones were screwed in. The control valve usually has a pressure-dependent rising pin with ring markings to indicate the pressure. Nowadays the valve is coupled with the lid lock so that the pot can only be opened without pressure to avoid accidents.
There are perforated and unperforated inserts for the pressure pots for cooking dishes, which do not come into contact with the still liquid cooking water, but are cooked in the steam.
function
With the pressure cooker, the actual cooking vessel is usually closed airtight and watertight by means of a locking mechanism ( bayonet lock ) with the lid and a seal. The resulting water vapor pressure makes it possible to reach a higher temperature than normal for cooking and thereby shorten the cooking times. Usually there is about 1.8 bar absolute pressure during operation in the pot , i. H. 0.8 bar overpressure ; This is not very much, but it increases the boiling temperature of the cooking water to around 117 ° C. The RGT rule states as a rule of thumb that the reaction speed increases 2 to 3 times with a temperature increase of 10 degrees (overall cooking is an interplay of different chemical reactions). The pressure cooker can be used to cook “lowland dishes” even at high altitudes where water cannot be heated to 100 ° C under normal conditions.
safety
A pressure cooker is a pressure vessel that has to undergo a type test before it can be placed on the market, as it falls within the scope of Directive 2014/68 / EU on pressure equipment . As an additional security against the existing risk of the pot bursting (e.g. if the control valve is stuck), a pressure cooker always has a safety valve that can safely reduce any overpressure.
In principle, a pressure display is not absolutely necessary, but since the necessary pressure control enables a display with the simplest of means, it is built in. Usually this is a stick that protrudes more or less from the lid depending on the pressure. In this way, the minimum heat supply required to maintain pressure is easy to set.
Pressure cooker from the 1860s. Made by Georg Gutbrod , Stuttgart
"Steam pot" from De Dietrich , Alsace , 1898.
Pressure cooker
200 liter cafeteria boiler Voss with stove pipe, Theodor Lessing House , Hanover
1960s pressure cooker
Individual parts of a modern pressure cooker
Photo 2: Lid from the outside
- Lid handle with slide for unlocking the lid and for relieving the pressure . The safety and relief valve in this design is located below the handle overhang for safety reasons.
- Outer cap of the control valve. By turning it, the cooking pressure (and thus the cooking temperature) can be regulated
- Pressure display, increases with the increase in pressure
Image 3: Lid from the inside
- Latch (unlocking lug) is activated by the slide on the lid handle
- Control valve
- Safety and relief valve, is opened by the slide. In this case a spring-loaded ball valve.
- Sealing ring. The recess in the lid, which serves as an additional safety valve, is covered by the sealing ring in the picture.
In order to be able to open (turn) the cover, the catch must first be drawn in with the slide on the cover handle (the cover unlocks). At the same time, the safety valve, now in its function as a pressure relief valve, is forcibly opened.
Fig. 4: Individual parts of the control valve
- The cap of the control valve is screwed onto the valve bushing from the outside with the assembled valve (the spring 5 of the control valve is thereby tensioned) and after assembly can be rotated at the end of the thread by a maximum of 180 °, whereby the contact pressure of the spring 5 is changed.
- Valve bushing with sealing O-ring and four holes for steam discharge
- Inner (fastening) nut of the valve leadthrough
- The socket of the control valve and the pressure indicator is inserted into the outer cap from above
- Control valve spring - regulates internal pressure
- Pressure gauge spring
- Pressure gauge dipstick
- Screw cap of the pressure indicator, sealing cone of the control valve
- Rubber cap, is put over the screw cap 8, moves the pressure indicator and seals the internal pressure against the sealing seat within the bushing item 2. When they are raised, the steam is blown off and escapes below the outer cap.
application
In addition to the food to be cooked (roast, jacket potatoes, fruit for juicing, etc.), a certain minimum amount of water is added to the pot and the lid is sealed gas-tight. When heated, some of the water evaporates and the pressure in the pot increases.
Before opening a pressure pot, the pressure must first be released: either via the valve (quick venting) or by cooling. The quick ventilation is only suitable for solid food: liquid food would splash, potatoes would burst with quick ventilation.
The correct function of the valves, which can be impaired, for example, by contamination, must be ensured. If the pressure is too high, steam can escape from the seal or the sudden evaporation of the water when opening under pressure can lead to scalding. In the worst case, the boiler can only burst (“ boiler crack ”) if there is insufficient maintenance . Such a pressure cooker can cause serious injuries or scalds, even with a relatively low overpressure.
The pressure display usually has two levels. The second (higher) level is the normal one, with which the preparation times are reduced by around 50-70% (with the higher pressure and temperature values mentioned above). The first level is suitable for sensitive food, where the cooking process takes a little longer, but still less than in a normal saucepan. Cauliflower florets on 'normal' (3–3.5 minutes) can hardly be obtained à point ; At level one it is easier to reach the right cooking time.
See also
Individual evidence
- ↑ Hervé This-Benckhard: Riddle of the art of cooking: explained scientifically . Berlin, 1996, p. 10.
- ↑ Thomas Müller: About the beginnings of clinical chemistry at the Berlin University (1810–1813): Georg Carl Ludwig Sigwart (1784–1864) as a pioneer of a new scientific discipline. Dissertation, Humboldt University, Berlin 1992.
- ↑ The true steam-tamer, Basler Zeitung 16 November, 2009 ( Memento of 22 February 2011 at the Internet Archive )
- ↑ PAT 2, 15 l, No. 252507 , State Archives of the Canton of Zurich, archive catalog
- ↑ Pressure cooker & cooking times guide: What takes how long? sunday morning.com
- ↑ Pressure cooker faq . Retrieved July 19, 2010.
