Chemical Defense

The Scoville Organoleptic Test was an archaic measurement that was used before there was an effective method of chemical analysis. In the test, the sample in question would be diluted and given to a panel of tasters. The number of panel members that could actually detect hotness would be counted. The sample would be further diluted and the process repeated until only a certain percentage of the panel could still detect hotness. The measurement was then calculated using the amount of dilution required before hotness could not be detected. The ratings were totally subjective because they would vary greatly from panel to panel as tolerance to hot food varies from person to person. Today, SHU is calculated using high-performance liquid chromatography. 

By government guidelines, pure capsaicin is rated at 15,000,000 SHU. The pepper scale ranges from a zero SHU for a bell pepper to around 5,000 SHU for a jalapeno pepper to an enormous 200,000 to 300,000 SHU for habaneras pepper. The oleoresin capsicum used in most pepper sprays is rated about 2,000,000 SHU. However, the SHU is fairly meaningless in the pepper spray business. The only true way to assess the hotness of any given formula is to have it chemically analyzed to assess the actual percentage of capsaicin. Since pure capsaicin is 15 million SHU, for a product to have 3 million SHU the product would have to be at least 20% capsaicin. 

Most sprays use food grade capsaicin, which is quite cheap, while some use pharmaceutical grade pure capsaicin, which is more expensive but makes a much cleaner and more effective product. Food grade OC is fairly low in capsaicin content and "heat," and is very heavy and oily, making it very difficult to dissolve and aerosolize.

A problem with a poorly formulated food grade capsaicin spray is that the capsaicin has a tendency to separate from the propellant. Being lighter than the propellant, the capsaicin floats to the top. Since spray cans are designed with dip tubes, the contents in the bottom of the can are expelled first when you spray. With a poor formula, this means you first discharge mostly propellant and when you finally do get to the pepper, rather than spraying as a fine aerosol, you get "beads" of pepper which are considerably less effective. Pharmaceutical grade pure extracted capsaicin is more expensive but you get a "hotter" product without aerosol problems.