The Scoville scale is based on a subjective test in which a panel of tasters, typically five, taste a sample of dried pepper that has been mixed with sugar water in decreasing concentrations until the heat can no longer be detected. The heat level of the pepper is then rated based on the number of times the sample must be diluted before the tasters can no longer detect its heat.
The rating is based on the Scoville Heat Units (SHU) and ranges from 0 for a bell pepper to over 2 million for the hottest peppers in the world, such as the Carolina Reaper. The scale is not linear, so a pepper with a rating of 1 million SHU is not just twice as hot as a pepper with a rating of 500,000 SHU.
Today, more objective methods such as High-Performance Liquid Chromatography (HPLC) are used to measure the concentration of capsaicin, the compound responsible for the spiciness of peppers, but the Scoville scale remains a popular way to compare the heat levels of different peppers and spicy foods.
We're currently working on measuring the HPLC for our sauces.