Thermometers And Temperature

Thermometers provide a reliable way to ensure that the food we consume is safe and to determine the "doneness" of meat, poultry, and egg products. By 'safety' we mean food-borne diseases caused by bacteria and other harmful microorganisms found in uncooked food, while "doneness" refers to food cooked to a desired state and indicates the sensory aspects of foods such as texture, appearance, and juiciness. Unlike the temperatures required for safety, these sensory aspects are subjective.

To be safe, foods must be cooked to an internal temperature high enough to destroy any harmful microorganisms that may be in the food; hence, the critical factor in controlling disease-causing microorganisms in food is controlling temperature. Pathogenic microorganisms grow very slowly at temperatures below 40 °F, multiply rapidly between 40 and 140 °F, and are destroyed at temperatures above 140 °F. For safety, foods must be held at proper cold temperatures in refrigerators or freezers and they must be cooked thoroughly.

According to the USDA, temperature is the only way to gauge whether food is sufficiently cooked. Its research reveals that the "color test" can give consumers misleading information about the safety of the foods they are preparing, since cooked color varies considerably. For example, freezing and thawing may influence a meat's tendency to brown prematurely.

However, to be effective, thermometers must be used properly and calibrated correctly. If the thermometer is inserted incorrectly, or placed in the wrong area, the reading may not accurately reflect the internal temperature of the product. In general, the thermometer should be placed in the thickest part of the food, away from bone, fat or gristle. Read the manufacturer's instructions on how to calibrate (check the accuracy of) the thermometer

Clearly the availability of a thermometer, in every kitchen, and a knowledge of temperature in relation to food and cooking is vital, in preventing undercooking, and consequently, food-borne illnesses.

TEMPERATURE

Temperature is a measure of the amount of heat energy possessed by an object. Because temperature is a relative measurement, scales based on reference points must be used to accurately measure temperature. There are three main scales commonly used in the world today to measure temperature: the Fahrenheit (°F) scale, the Celsius (°C) scale, and the Kelvin (K) scale. Each of these scales uses a different set of divisions based on different reference points as described in detail below.

Daniel Gabriel Fahrenheit (1686-1736) was a German physicist who is credited with the invention of the alcohol thermometer in 1709 and the mercury thermometer in 1714. The Fahrenheit temperature scale was developed in 1724. Fahrenheit originally established a scale in which the temperature of an ice-water-salt mixture was set at 0 degrees. The temperature of an ice-water (no salt) mixture was set at 30 degrees and the temperature of the human body was set at 96 degrees. Using this scale, Fahrenheit measured the temperature of boiling water as 212°F on his scale. He later adjusted the freezing point of water from 30°F to 32°F, thus making the interval between the freezing and boiling points of water an even 180 degrees (and making body temperature the familiar 98.6°F). The Fahrenheit scale is still commonly used in the United States.

Anders Celsius (1701-1744) was a Swedish astronomer who is credited with the invention of the centigrade scale in 1742. Celsius chose the melting point of ice and the boiling point of water as his two reference temperatures to provide for a simple and consistent method of thermometer calibration. Celsius divided the difference in temperature between the freezing and boiling points of water into 100 degrees (thus the name centi, meaning one hundred, and grade, meaning degrees). After Celsius’ death, the centigrade scale was renamed the Celsius scale and the freezing point of water was set at 0°C and the boiling point of water at 100°C. The Celsius scale takes precedence over the Fahrenheit scale in scientific research because it is more compatible with the base ten format of the International System (SI) of metric measurement. In addition, the Celsius temperature scale is commonly used in most countries of the world other than the United States.

Lord William Kelvin (1824-1907) was a Scottish physicist who devised the Kelvin (K) scale in 1854. The Kelvin scale is based on the idea of absolute zero, the theoretical temperature at which all molecular motion stops and no discernable energy can be detected (see the molecular motion lesson for more information). In theory, the zero point on the Kelvin scale is the lowest possible temperature that exists in the universe: -273.15ºC. The Kelvin scale uses the same unit of division as the Celsius scale, however it resets the zero point to absolute zero: -273.15ºC. The freezing point of water is therefore 273.15 Kelvins (graduations are called Kelvins on the scale and neither the term degree nor the symbol º are used) and 373.15 K is the boiling point of water. The Kelvin scale, like the Celsius scale, is a standard SI unit of measurement used commonly in scientific measurements. Since there are no negative numbers on the Kelvin scale (because theoretically nothing can be colder than absolute zero), it is very convenient to use Kelvins when measuring extremely low temperatures in scientific research.

THERMOMETER AND TEMPERATURE IN THE ASIAN KITCHEN

About thermometers and temperatures

WHY THERMOMETERS ARE ESSENTIAL IN THE KITCHEN

TEMPERATURE