Posted: 10/13/2012 12:17:43 PM
A basic slow cooker consists of a lidded round or oval cooking pot made of glazed ceramic or porcelain, surrounded by a housing, usually metal, containing an electric heating element. The lid is often of glass
seated in a groove in the pot edge; condensed vapour collects in the
groove and provides a low-pressure seal to the atmosphere. The contents
of a crock pot are effectively at atmospheric pressure, despite the
water vapor generated inside the pot. A crock pot is quite different
from a pressure cooker and presents no danger of an abrupt pressure release.
The ceramic pot, or 'crock', acts as both a cooking container and a heat reservoir.
Slow cookers come in capacities from 500 ml (16 oz) to 7 liters (7.4 US
quarts). Due to the placement of heating elements (generally at the
bottom and often also partway up the sides), there is usually a minimum
recommended liquid level to avoid uncontrolled local heating.
Many slow cookers have two or more heat settings (e.g., low, medium,
high, and sometimes a "keep warm" setting); some have continuously
variable temperature. A typical slow cooker is designed to heat food to
77 °C (170 °F) on low, to perhaps 88-93 °C (190-200 °F) on high. Many
recipes that include sauce or liquid will reach the boiling point around
the edges, while food in the center remains gently cooked. This may be
because slow cooker settings are based on wattage, not temperature.
Raw food and a liquid (such as water, wine, or stock) are placed in
the slow cooker. Some recipes call for pre-heated liquid. The cooker lid
is put on and the cooker is switched on. Some cookers automatically
switch from cooking to warming (maintaining the temperature at 71–74 °C
[160–165 °F]) after a fixed time or after the internal temperature of the food, as determined by a probe, reaches a specified value.
The heating element heats the contents to a steady temperature in the
79–93 °C (175–200 °F) range. The contents are enclosed by the crock and
the lid, and attain an essentially constant temperature. The vapor that
is produced at this temperature condenses on the lid and returns as
liquid. Some water-soluble vitamins are leached into the liquid.
The liquid transfers heat from the pot walls to its contents, and
also distributes flavours. A lid is essential to prevent warm vapour
from escaping, taking heat with it and cooling the contents.
Basic cookers, which have only high, medium, low, or keep warm
settings, have to be manually turned on and off. Others have settings
for high and low (e.g., four hours high, eight hours low) which allow
the cook to choose a cooking time after which the cooker switches to
"keep warm" mode. The most advanced cookers have computerised timing
devices that allow the cooker to be programmed to perform multiple
operations (e.g. two hours high, followed by two hours low, followed by
warm) and to delay the start of cooking.
Because food stays warm for a long time after switching off, slow
cookers can be used to cook food to be taken to be eaten elsewhere
without reheating. Some cookers have ways of sealing the lid to prevent
the contents from spilling during transport.
Cheaper cuts of meat with connective tissue and lean muscle fibre are suitable for stewing, and tastier than stews using expensive cuts,
as long slow cooking will soften the connective tissue without
toughening the muscle. Slow cooking leaves the gelatinised tissue in the
meat, so that it may be advantageous to start with a richer liquid.
The low temperature of slow-cooking makes it almost impossible to
burn food even if cooked too long; however, some meats and most
vegetables will become nearly tasteless or "raggy" if overcooked.
Food can be set to slow-cook before leaving for the day, and will be
ready on return. Some models include timers or thermostats which bring
food to a given temperature, and then lower it. With a timerless cooker
it is possible to use an external timer to stop cooking after a set
time, or both to start and stop.
Cooking the meal in a single pot reduces washing up, and the low cooking temperature and glazed pot make cleaning easy.