Slow cooker

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A slow cooker. This one has a removable 'pot' (upper left), lid (lower left), and heater/housing (right).

A slow cooker, often referred to as a Crock-Pot®, is a countertop electrical home appliance that is used to cook stews and other dishes containing water at relatively low temperatures, with correspondingly long cooking times (several hours). Many recipes simply call for the ingredients to be put in the crock, with little preparation. The slow cooker can then safely be left to run unattended, making it a convenient cooking method.

1 History
2 What it is
3 How it works
4 Cooking with a slow cooker
5 Pros and cons
6 See also
7 Notes and references
8 External links

[edit] History

The modern slow cooker was developed by Rival Industries with the trademarked name Crock Pot. This name is sometimes used informally to refer to any slow cooker. Rival purchased and refined the design of a bean-pot called the Beanery from Naxon Co. of Chicago.[1]

[edit] What it is

An oval crock pot cooking.

A slow cooker consists of a lidded round or oval pot (typically 10 in (25 cm) across and similarly deep) made of glazed ceramic or porcelain, surrounded by a housing, usually metal, containing a thermostatically controlled electric heating element. The lid is often made of glass so that users can see the contents without having to remove it, and is not hermetic. The ceramic pot, often referred to as a crock, acts as both a cooking container and a heat reservoir. Slow cookers come in a variety of sizes, with capacities starting as small as 16 oz. and going up to several quarts.

Many slow cookers have two or more temperature settings (e.g., low, medium, and high). A typical slow cooker operates at 80°C (176°F) on low, 90°C (194°F) on high, and 1 hour at 90°C followed by 80°C on medium.

[edit] How it works

Raw food and a liquid which is predominantly water (water, wine, stock, but not oil without water) are placed in the slow cooker. The lid is put on and the cooker is switched on. The heating element and thermostat heat the contents to a steady temperature in the range 175–200°F (80–95°C). The temperature can never exceed the boiling point of water at atmospheric pressure, as the non-hermetic lid does not allow pressure to build up. The contents are enclosed by the crock and the lid, and attain an essentially constant temperature. Little vapor is produced due to the low temperature, and condensed vapor tends to form around the lid, keeping evaporation very low. Vapor may condense on the lid and fall back on the contents, keeping them moist if above the liquid level.

The liquid has the important function of transferring heat from the pot walls to the contents, and it also distributes flavours. A lid must be used to prevent warm vapor from escaping, cooling the contents. The lid should not be removed to stir the food or for any other reason, as this would significantly prolong required cooking time due to heat loss.

By contrast, a pressure cooker cooks quickly at temperatures well above 212°F (100°C) using steam at high pressure and temperature, as it is hermetically sealed. Unlike a pressure cooker, a slow cooker cannot explode even without a safety valve as the contents are at atmospheric pressure. Ovens broil at 600°F (320°C), and bake at 300 - 500°F (150 - 260°C). Water-based foods in saucepans are often cooked at the boiling point of water. A lower temperature can be used, but is difficult to maintain accurately.

[edit] Cooking with a slow cooker

Recipes intended for other cooking methods must be modified for slow cookers. Often water must be decreased, as cooking at higher temperatures requires enough liquid to allow for evaporation. Some slow cookers are supplied with recipe booklets; many slow cooker recipes are to be found in cookbooks and on the internet. 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 gives good results even with cheaper (and tougher) cuts of meat—in fact, cheaper cuts often have more flavour.

[edit] Pros and cons

[edit] Hard to overcook

In a slow cooker, the temperature is low enough to avoid badly overcooking food even if cooked for far longer than necessary. However, meat may become nearly tasteless if overcooked. Some foods are better cooked at temperatures below boiling. In particular, the tough connective tissues of meat are broken down without affecting the texture of the meat.

[edit] Nutrition

Cooking with a slow cooker does have some disadvantages. Vitamins and other trace nutrients are lost, particularly from vegetables, partially by enzyme action during cooking. When vegetables are cooked at higher temperatures these enzymes are rapidly denatured and have less time in which to act during cooking. Blanched vegetables, having been exposed to very hot water, have already had these enzyme rendered largely ineffective. Since slow cookers work at temperatures well below boiling point and do not rapidly denature enzymes, vegetables tend to lose trace nutrients. Green colors are retained better when vegetables are cooked quickly as plant cells are less likely to lose acids.

[edit] Food safety

Slow cooker temperatures are lower than in most other cooking methods, and cooking times are correspondingly longer—typically 5–9 hours. Food must be heated to a temperature of at least 140°F (60°C) for safety; a properly functioning slow cooker must heat food to this temperature. As with any cooking method, cooked food must not be left at warm temperatures for long.

Frozen food should be defrosted before slow cooking. Defrosting should either be done at a low temperature to inhibit bacterial growth (i.e., in a refrigerator), or done quickly (i.e., in a microwave oven). Otherwise bacteria may multiply while the food is heating but has not yet attained a safe temperature to inhibit growth. Some bacteria produce toxins that remain in the food after the bacteria themselves are killed. Most, but not all, toxins are destroyed at high temperatures; the botulism toxin is one important exception, although the micro-organism which produces it is killed both by heat and oxygen.

Some foods contain toxins naturally. Many, but not all, of these are destroyed by cooking at slow cooker temperatures. However some legumes are toxic when cooked at slow cooker temperatures, especially kidney beans, and can cause food poisoning.^[1] To avoid this problem, such ingredients should be boiled for 10 minutes beforehand.

Perpetual stews (pot au feu, olla podrida) should never be maintained in slow cookers, as slow cookers do not typically provide sufficient heat to compensate for frequent additions and removals of food; nor do they cook quickly enough to cook newly added food thoroughly before the next withdrawal becomes likely. This relatively slow recovery of temperature after an addition or withdrawal may cause safety problems. Removal of the lid lets heat and moisture escape, prolonging cooking time and giving microbes the chance to grow.

[edit] Other hazards

Because these cookers are hot, easily moved, contain large quantities of hot food and water, and are left unattended during long cooking times, they are dangerous to small children and exploratory pets, who must be kept away by reliable means. Electrical failures can cause problems, including fires. Although slow cookers have few parts that can fail in a dangerous way, and failures are rare, unattended slow cookers must be treated with respect and caution. For instance, they are best used in a kitchen placed on a tile or similarly reduced flammability surface, and not near flammable materials such as papers or flammable fluids since the outside of the slow cooker becomes hot during operation. Fire risk is minimized by keeping the appliance away from surrounding flammables.

[edit] See also

Cholent (Jewish recipe that may be prepared with the appliance)
Vacuum flask cooking
Low temperature cooking

[edit] Notes and references

^ Phytohaemagglutinin, US FDA's Bad Bug Book or Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. Kidney beans may be five times more toxic if cooked at 80 °C than if eaten raw.