Pressure Cookers

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Introduction - Technology

Pressure cookers are special cooking pots that can be sealed airtight and allow pressure to build up inside. A mechanical device (screws or interlocking parts) presses the pot-lid firmly against the pot-body. A gasket or seal in between the lid and the pot prevents steam to escape from the pot. With rising heat, the steam pressure inside the pot builds up beyond atmospheric pressure, allowing the temperatures to rise well above boiling point. This design enables to save time, energy, and resources. The temperature inside a pressure cooker can well go beyond 110° C, which reduces the time needed to cook food. In addition, very little steam escapes between the pot and the lid, thus requiring less water to cook the food.

Market and Field of Application

So far, pressure cookers have often been overlooked as potential components of efficient integrated cooking systems. They are normally made from thick aluminium or stainless steel, which makes them heavier and more expensive than conventional pots. They might also be difficult to produce in many developing countries. Prices are seldom below 20 US$, top-of-the range products easily exceed 200 US$. In regions, where pressure cookers are not commonly used, the relatively high costs of purchase are an obstacle for their spread out. Pressure cookers are more popular in urban areas, where the fuel has to be paid for in cash, and in regions, where local food can easily be cooked with pressure cookers: especially in Asia (China, Nepal, and India).

Worldwide, different models of pressure cookers are offered on markets. In order to find the most appropriate model, different features have to be taken into consideration, such as price, size, main kind of stove applied (electric, gas, fire), durability, and maintenance. Additionally, the replacement of the seals is an important point to consider. The following pictures show examples of pressure cookers found during a market analysis in Tajikistan in 2010/2011.

Afghan pressure cooker, without any plastic parts. (Picture: Heike Volkmer)	Chinese model (Picture: Heike Volkmer)
Pressure cooker (Picture: Friederike Müller)	Old Soviet pressure cooker (Picture: Friederike Müller)

Pressure cookers can be used with nearly any stove and fuel type. When used on an open wood-fire, however, care should be taken that non-metal parts do not get exposed to the flames, otherwise they might melt or burn.

Pressure cooker can also be used in combination with a fireless cooker, such as a heat retention bag or box (discussed later). With this type of combination, fuel savings of 80% were measured in a test in Tajikistan carried out with Welthungerhilfe. If the pot is put into a heat retention bag or box before the pressure valve releases steam, no energy in form of steam is lost. Information such as cooking time to boil, cooking time after boil is reached, and time required for the pot to remain in the heat bag are necessary for, e.g, instruction manuals. This information depends on the altitude, food to be cooked, and type of pressure cooker and heat retention bag.

Pressure cookers can also be utilized for cooking traditional cooking recipes. However, user training and awareness training are necessary to show users how to cook traditional recipes on the new equipment. One example of doing this is to handout a pressure cooker cookbook for traditional dishes.

In higher altitudes the low atmospheric pressure reduces the boiling point of water. Therefore the cooking is slower and requires more fuel or food remains undercooked. The required boiling time for softening the food is between one fourth and one fifth of the normal boiling time, depending on the altitude.

As the steam within the pressure cooker creates a higher boiling temperature, the potential of pressure cookers to save fuel and cooking time rises with increasing altitudes, as shown in the following table:

Altitude in meters	Sea level	1000 m	1500 m	2250 m	3000 m	Pressure cooker A
Boiling temp. degrees Celsius	100 ºC	96.6 ºC	95 ºC	92.2 ºC	90 ºC	118 ºC ~ 120 ºC

Advantages of Pressure Cookers

• Pressure cookers can be used with most fuel types and stoves.
• At high altitudes where the boiling point is lower, they offer great advantages to raise the temperature above 100°C and prevent food from being left undercooked.
• Cooking is much faster and thus the pressure cooker can save considerable amounts of time and energy.
• It is possible to sterilise goods using a pressure cooker.
• Nutrients and flavors are retained: Because foods cook quickly with a small amount of liquid in an almost airless environment, vitamins and minerals that are normally boiled away in the cooking process condense in the pot and absorb back into the food retaining the precious nutrients naturally found in our food.

Disadvantages of Pressure Cookers

• More expensive than normal pots.
• As steam builds up inside, they cannot be used for frying or roasting.
• Can not be used for foods that need to be stirred during cooking (like maize porridge).
• Opening the cooker must be done carefully since hot steam, under pressure, can escape with force and scald the cook.
• Pressure cookers are not appropriate for dishes, where different ingredients need to be added at different times, as they cannot easily be opened during cooking.
• Seal between the pot and the lid wears out and must be replaced; thus a service system has to be in place.
• Cooking with a pressure cooker requires the change of accustomed cooking processes (behaviour change).
• Due to the hotter steam the risk of scalding is higher.

Safety Aspects

If appropriately used and maintained, pressure cookers are safe to use. However, several important considerations should be kept in mind. To prevent explosions, regulators and safety valves let surplus pressure escape. It is really important that the safety valve and regulator are fully functional. Pressure cookers should never be filled until the top of the pot, as the regulator and the valve can get blocked easily. In case of too high pressure the steam can abruptly escape, which can lead to scalding. In addition, pressure cookers made from aluminium should not be cleaned with sharp items or with soda, as afterwards aluminium can enter the food, which will cause diseases.

Unfortunately, if the pressure cooker is poorly maintained or inappropriate used, the cooker can explode, which can result in serious injuries.

Further Information

• Everything about pressure cookers: Pressure-Cooking Times & Instructions: fastcooking.ca - pressure cookers

http://discoverpressurecooking.com/index.html

• Manual on Pressure Cookers (*Russian): Manual PRESSURECOOKER

References

This article was originally published by GIZ HERA. It is basically based on experiences, lessons learned and information gathered by GIZ cook stove projects. You can find more information about the authors and experts of the original “Cooking Energy Compendium” in the Imprint.

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