How is the heat in Peppers measured?
In 1912, Wilbur Scoville, a chemist, developed a unit to measure the head in chilli peppers that is still used today, the Scoville Heat Unit. His original test was a taste test where ground chilli peppers are diluted in sugar water and tasted. More sugar is added until the heat can't be tasted. According to the Guinness Book of World Records, the Red Savina Habanero is the hottest pepper on Earth with a rating of 570,000 SHU.

What makes the pepper hot?
Capsaicin, a crystalline alkaloid is produced by the pepper and is responsible of the heat. Capsaicin is incredibly powerful and seemingly unaffected by heat or cold so it stays potent despite cooking or freezing. Because it is colorless and odorless, it can only be measured in a laboratory.