Calorie

Calorie (Latin calor, heat '; unit symbol cal) is an obsolete unit of energy, especially the heat quantity Q, with several slightly different definitions. Already in 1948 abolished the 9th General Conference on Weights and Measures in Paris the calorie as a unit of heat quantity in favor of the unit joules. A calorie equivalent to about 4.1868 joules ( 1 kcal = 4.1868 kJ ) and a Joule approximately 0,239 calories. Due to different definitions of the calorie however, there are slightly different values ​​. In Germany the use of Joule as an international SI unit of energy is required by law since 1969. In the EU of goods an additional element in the unit calorie is permitted by the recent Directive of 2010 addition to stating in Joule as a unit of energy. In food products, the additional disclosure may take place only in kilocalories (kcal).

Use

The word " calorie" may refer to a calorie ( 1 cal ) or kilocalories ( 1 kcal ) relate and is correspondingly imprecise. Both uses were and are common. To distinguish one sometimes speaks of " Grammkalorie " and " Kilogrammkalorie " or " small calorie" and " large calorie", each of which relates to the heating of one gram or one kilogram of water by one degree Celsius. Clearly, however, in practice, the label " kcal " for 1000 gram calories, analogous to the intentions for SI units.

Use in Physics

In physics, the calorie understood after the introduction of the CGS system, generally as Grammkalorie. Although the amount of heat could be expressed (based on ohms and volts ) through the CGS unit of energy, Erg, and also the Joule from the parallel practical electromagnetic system was often the desire to keep a special unit of the amount of heat on the specific heat capacity of water is based. Water has played a crucial role in the decision for the CGS system and against a system with meters instead of centimeters as the basic unit of length, because its density is thus in the basic units of approximately 1. It was not clear in 1900, first naming, and clear definition for such a unit, especially the question of whether they should be discharged through a fixed numerical value from joules or ergs or defined by a separate measurement specification.

Subsequent normalization of calorie have always taken this as a basis Grammkalorie and defines a fixed numerical value for conversion from other units; next on have measurement-based definitions exist. A single use, it is not come before the calorie has been increasingly replaced by the Joule.

Use as nutrition information

Often, in particular the energy content or energy value of food is still additionally be used to reference in kilojoules into kilocalories; the EU Directive on nutrition labeling wrote since 1990 requires disclosure both in kJ and kcal. On the other hand, the SI units must be used in the economy and public health of the EU always; compared with other specified other units they must be highlighted. In particular, a specification in kcal must not be set in a larger font.

Since 1 January 2010, the calorific value of the food in the EU must be uniform in kJ based on a certain amount - for example, in kJ per 100 g - be given, with the additional information on the energy value is allowed without time limitation in kcal. A deadline for the abolition of the additional use of the calories as a unit in the movement of foodstuffs was initially set to start in 1990 and then extended to the beginning of 2000; the last extension until the end of 2009 and the complete abolition of time limit is justified by trade barriers when exporting to third countries. From the beginning of 1978 (the end of the transitional period of the earlier Directive ) until the end of September 1981 ( the date of the previous policy ) was the use of calorie in the EU prohibited.

Colloquially nutritional information in kilocalories are erroneously referred to as " calories " often. In the U.S., at the Nutrition Facts label for calorie calories officially permitted.

The recommended daily requirement for adult humans varies depending on gender and age. Average it is about 8-13 MJ (2-3 Mcal / 2,000-3,000 kilocalories ), while active high performance athletes may need twice without further notice.

The Austrian heavy labor regulation defines heavy physical work, inter alia, as if in an eight-hour working time of men at least 8,374 kilojoules (2,000 calories ) and women at least 5,862 kilojoules ( 1,400 kilocalories ) consumed ( § 1 para 1 4 heavy labor regulation).

Definitions

In principle, all definitions referring to the calorie amount of heat required to heat a certain mass of water, 1 g and 1 kg, about 1 Kelvin, that the specific heat capacity of water. This value is, however, significantly depends on temperature; next to it also depends on the ambient pressure and the type of water used ( chemical purity, isotopic composition ).

Liquid water has a minimum of the specific heat capacity at about 30-50 ° C of just 4.18 kJ / (kg · K) at 0 ° C and 100 ° C are there in each case to the 4.22 kJ / (kg · K ). Accordingly, there are different definitions of calorie. Some of them only define the measurement provision in which a value with a certain level of reliability can be determined; others define an exact conversion factor to other units.

Initially ( mid 19th century ) was a reference to the heating of water from 0 ° C to 1 ° C in use, so a rather high value of about 4.22 kJ per Kilogrammkalorie; later was a standardization of Grammkalorie to exactly 42 million ergs, corresponding to 4.2 J, talking.

The international standard ISO 80000-5 lists as its predecessor ISO 31-4 3 definitions of the ( gram ) calorie in Appendix B, but disapproved of their use:

Other common definitions refer to the specific heat capacity of water at 4 ° C ( maximum density, and approximately 4,204 J) or 20 ° C (reference temperature for liquid food products in the EU, about 4,182 J ); other reference points in the range of typical laboratory temperatures were common.

The International Union of Nutritional Sciences ( IUNS ) adopted a value of exactly 4.182 J.