Slow cooker
A slow cooker 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 cooker with little preparation. The slow cooker can then safely be left to run unattended, making it a convenient cooking method.
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]
Slow cookers contrast with pressure cookers, which are hermetically sealed and cook quickly at temperatures well above 100°C (212°F) using steam at high pressure and temperature. Unlike a pressure cooker, a slow cooker cannot explode even without a safety valve as the contents are at atmospheric pressure. Ovens broil at 320°C (600°F), and bake at 150 - 260°C (300 - 500°F). 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.
Design
A slow cooker consists of a lidded round or oval cooking pot (typically 25 cm (10 in) 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 pot, acts as both a cooking container and a heat reservoir. Slow cookers come in a variety of sizes, with capacities starting as small as 500 ml (16 oz). and going up to several liters (quarts). Note however, that due to the placement of heating elements, there is generally a minimum fill size for most crock pots to achieve proper operation; failure to sufficiently fill with water and food can even destroy the crock from uncontrolled local heating at the level of the heating coil.
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. Some slow cookers sold in the US in the past several decades did not slow cook at all: all of the settings brought the contents to a full boil, with the only difference in setting being the amount of time to come to a boil. This may have been due to concerns about product liability from unsafe food holding temperatures.[citation needed]
Operation
Raw food, and a liquid which is predominantly water, such as water, wine, stock, (but not oil without water), are placed in the slow cooker. Some recipes work best if the liquid which is added to the other ingredients has been already heated to boiling point, for example, in a kettle. The cooker lid is put on and the cooker is switched on. It may have different heat settings, typically, high, medium and low, and the recipe should indicate which is appropriate. Some slow cookers also have an Auto setting, which switches the element on and off over time. The heating element heats the contents to a steady temperature in the 80–95°C (175–200°F) range. 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 (unless specifically mentioned in a recipe for the slow cooker), as this would significantly prolong required cooking time due to heat loss.
Recipes
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, timing 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.
Advantages
In a slow cooker, the temperature is low enough to avoid badly overcooking food even if cooked for far longer than necessary. However, success will rely on careful timing, as in all cooking. Meat may become nearly tasteless or "raggy" if overcooked, but the slow cooking process is especially useful to tenderize cheaper cuts. 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. Slow cookers enjoyed a surge of popularity in the 1970s and 1980s, as former housewives joined the workforce and enjoyed the prospect of a hot meal available on returning home from work. The lengthy cooking times allowed them to start dinner cooking before leaving for work. Overnight cooking, utilizing economy rated power, cuts the cost of the meal. For best results, many cooks part-cook root vegetables and sear meat prior to inclusion; then the slow cooker finishes the process of blending flavours, adding convenience and reducing washing up, as this is a "one pot" cooking method.
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. Since slow cookers work at temperatures well below boiling point and do not rapidly denature enzymes, vegetables tend to lose trace nutrients. Blanched vegetables, having been exposed to very hot water, have already had these enzyme rendered largely ineffective, so a blanching or sauteing pre-cook stage will leave more vitamins intact. Green colors are retained better when vegetables are cooked quickly as plant cells are less likely to lose acids.
Kidney beans, and some other beans, contain a toxin, phytohaemagglutinin, which is destroyed by cooking at boiling point but not at the operating temperature of a slow cooker. They become safe to eat after boiling for a minimum of ten minutes, or if they come from a can. Such precautions must be observed if kidney beans are included in slow cooker recipes, as the relatively low temperatures in a slow cooker will not destroy the toxin adequately, and serious food poisoning may occur.[2] Kidney beans can be as much as five times more toxic if cooked at 80 °C than if eaten raw, so exposing them to a high temperature for an adequate time prior to slow cooking is vital.
Slow cookers do not typically provide sufficient heat to compensate for frequent additions and removals of food in perpetual stews (pot au feu, olla podrida); 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.
Like all pottery, some slow cookers crocks may have been glazed with a formula containing lead.[3] Lead is a toxic metal, causing neurological and developmental damage in even small quantities, and it is not easily cleared from the body, so its dangers continue.
See also
References
- ^ http://www.slate.com/id/2113226
- ^ Phytohaemagglutinin, US FDA's Bad Bug Book or Foodborne Pathogenic Microorganisms and Natural Toxins Handbook.
- ^ http://hgic.clemson.edu/factsheets/HGIC3864.htm
External links
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