In food preparation, a crock-pot (also crock pot) is the name given by some manufacturers to their brands of slow cookers. It is a trademarked term in many countries, but is often used generically. When used to refer to the trademarked brand of cooker, both words are capitalized.
This type of slow cooker consists of a pot (typically 10" (25 cm) across and similarly high) made of fired clay and usually glazed, surrounded by a housing, usually metal, containing a thermostat controlled electric heating element. The ceramic pot, often referred to as a crock, acts as both a cooking container and a heat reservoir. Many crockpots have two settings for power. Crockpots have loosely fitting lids (often of glass or similar material) to retain moisture and heat.
Cooking in these appliances is done at atmospheric pressure since the lid is not pressure tight (and indeed is 'sealed' only by condensed vapors and gravity); thus, as long as water remains in the pot, internal temperatures can go no higher than the boiling point of the fluid (for water at sea level this is 212 F / 100 C). The physics of boiling_point prohibit a temperature of the contents above the boiling point while there is still liquid changing into vapor (most of which condenses back into the crock and so returns moisture to the contents). In this respect, a crockpot is very different than a pressure cooker, which, though it also cooks using vapor, has both elevated pressures (steam in this case) and temperatures. There is some danger of explosion from the increased pressure, which is why maintenance of the pressure relief valve is critical for pressure cookers; in contrast, no correctly used crockpot can explode since no increase in internal pressure occurs. The outside temperature of a crockpot can be expected to exceed the boiling point of water to facilitate heat transfer to the crock and to the food.
In use, the food is placed inside the pot, immersed in water, the lid applied, and the unit switched on. Cooking times vary with the recipe and with the food quantity, but are typically several hours. Temperatures are low in comparison with traditional ovens used for broiling (typically 600 deg F or higher) and baking (typically 300-500 deg F). Cooking is sufficiently slow that, if the food is not removed promptly at the specified time, little harm is done.
The water and its proper level is important, for it serves both as the heat conduction mechanism between the pot walls and the food, and as the flavoring (herbs and spices) distribution method and a 'basting' mechanism. No stirring is required (or recommended) since removing the lid during cooking causes significant cooking delays. The lid is important as it prevents escape of hot water vapor which would, if permitted, lead to lowering the internal water level, loss of heat and drying out of the contents.
Recipes for these cookers must be adjusted to compensate for the nature of the cooking: often water must be decreased. Most (probably all) come with recipe booklets; many cookbooks with crock pot recipes are available and there are numerous recipes on the Web. A small number of cookbooks seek to make complete dishes in a crockpot using fewer than five ingredients while others treat the crockpot as a serious piece of culinary equipment capable of producing gourmet meals. With some experience, timings and recipe adjustments can be successfully made for many recipes not originally intended for these cookers. The long, moist nature of the cooking method allows for lower quality cuts to be used.
Safety: Cooking temperatures are lower than many other cooking methods, and cooking times are lengthy, so some have been concerned about the growth of micro-organisms. Crock pots are capable of boiling their contents. Boiling is sufficiently hot enough to cook all meats including poultry, which requires the highest internal temperature of all meats. If the temperature control is working correctly, and if food is not left to stand more than briefly at room temperature, there is little problem. Fill the pot, add water, and promptly turn the unit on; this will avoid such problems.
If the starting food ingredients are frozen, it may take a long time for the pot to rise to proper cooking temperature. During this prolonged temperature climb, the microbes in the food can multiply. The microbes will be eventually entirely killed before the food is served, and so will themselves present little problem. But some microbes produce toxins which remain even after the microbes have expired. Most such are proteins which are themselves destroyed by the heat of cooking; but some of these cannot be destroyed by cooking -- as for example botulism toxin. In actual practice, most such heat resistant toxins are produced by anaerobic microbes which cannot survive in the presence of oxygen (e.g., the boulism organism). The combination of contact with the atmosphere (ie, with oxygen) and cooking heat disposes of nearly all such problems. As in all cases with frozen food (crock pots are not unique in this regard), one safeguard is to defrost frozen ingredients at low temperatures at which microbes don't do well (ie, in the refrigerator), or to defrost them more quickly (eg, in a microwave or a conventional oven), before putting them into the crock pot.
Perpetual_stew should not be maintained in crock pots as the crock pot cools off slow enough to encourage the growth of microbes. The repeated removal of the lid also interferes with cooking (primarily via loss of heat and moisture) and one result may be too low a temperature to deter microorganism growth for prolonged periods.
Warning: Because these cookers are portable/movable, contain large quantities of hot food and water, and because they are left unattended during long cooking times, they are dangerous around small children and exploratory pets. Cooking areas should be blocked off -- effectively -- if either might be present without responsible supervision. Like all electrical appliances, failures (in the electrical wiring or the control mechanisms) can cause problems, including fires. Although crock pots have few parts that could fail and reports of their failures are rare, unattended crock pots should be nonetheless treated with respect and caution. For instance, they are best used in a kitchen placed on a tile or similarly reduced flammabilty surface, and not near flammable materials such as papers or flammable fluids since the outside of the crockpot does become warm during operation. The fire risk is certainly minimized by isolating the appliance from surrounding flammables.
See also: Vacuum flask cooking