The slow cooker, likewise known as the crock-pot or even crock pot (this title is trademarked in numerous countries, however typically utilized generically. While these come non utilized generically, each words are capitalized.) occurs as preparation device consisting of the pot (usually X" (25 cm) across and similarly high) made of fired clay and usually glazed, surrounded by a housing, usually metal, containing a thermostatically controlled electric heating element. The ceramic pot, often referred to as a crock, acts as both a cooking container and a heat reservoir. Many slow cookers have two settings for power. Slow cookers 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 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 slow cooker 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 slow cooker can explode since no increase in internal pressure occurs. The outside temperature of a slow cooker 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 slow cooker recipes are available and there are numerous recipes on the Web. A small number of cookbooks seek to make complete dishes in a slow cooker using fewer than five ingredients while others treat the slow cooker 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.

Food safety

Using a slow cooker, temperatures are lower than in many other cooking methods, and cooking times are lengthy. Because of this, some people have been concerned about the growth of micro-organisms. Slow cookers are capable of boiling their contents. Boiling is sufficiently hot to cook all meats, including poultry, which requires the highest internal temperature to be safe for consumption. If the temperature control mechanism is working correctly, and if food is not left to stand more than briefly at room temperature, there are few problems. Filling the pot, adding water, and then promptly turning on the unit will avoid such problems as well.

If the starting food ingredients are frozen, it may take a long time for the pot to reach proper cooking temperature. During this slow heating, microbes in the food can multiply. The microbes will eventually be killed before the food is served, and so themselves pose little risk. But some microbes produce toxins which remain even after the microbes have died. Most such toxins are proteins which are destroyed by the heat of cooking, but some such toxins cannot be destroyed by cooking -- for example, botulism toxin. In practice, most such heat resistant toxins, including those that cause botulism, are produced by anaerobic microbes which cannot survive in the presence of atmospheric oxygen. Heat also kills these organisms. As with any cooking technique, when cooking frozen food, do not defrost at room temperature. A safer technique is to defrost ingredients in a cold evironiment, usually a refrigerator, where the temperature is too low for the microbes to thrive. Alternatively, one may defrost foods using a microwave oven so that the bacteria have little time to grow.

Perpetual stews should not be maintained in slow cookers, as the slow cooker cools off slowly enough to encourage the growth of microbes. The repeated removal of the lid also lets heat and moisture escape, prolonging cooking time and giving microbes the chance to grow.

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 slow cookers have few parts that could fail and reports of their failures are rare, unattended slow cookers 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 slow cooker does become warm during operation. The fire risk is certainly minimized by isolating the appliance from surrounding flammables.