Part 3/6:
Defining and measuring calories, particularly in food, can be problematic. One major difficulty lies in the variation of starting temperatures when measuring energy. Historically, different definitions of calories were used, such as the 15-degree calorie, which was based on heating one gram of water at standard atmospheric pressure from 14.5°C to 15.5°C. This older definition measured approximately 41.855 joules.
Current standards, governed by organizations like the International Union of Nutritional Sciences (IUNS), have converged on defining a calorie as equal to approximately 4182 joules. It's essential to understand these nuances when considering calorie content in dietary contexts.