The Scoville scale is the world recognised scale for measuring the heat in chillies and other peppers.
The Scoville scale was created in the early 1900’s by Wilbur L. Scoville who was a pharmacist.
Scoville’s method was simple. He soaked each different variety of pepper separately in alcohol overnight. Because capsaicin is soluble in alcohol, the soaking extracted the pungent chemicals from the pod. Then he took a precise measure of the extract and to it added sweetened water in incremental portions until the heat was barely detectable on his tongue.
In the case of Japan chiles, it took sweetened water in volumes between 20,000 to 30,000 times the pepper extract before the heat was barely discernible. He thus rated the Japan chiles 20,000 to 30,000 Scoville Heat Units. Jalapenos were rated 3,000 to 5,000, and Tabasco 30,000 to 50,000. The hottest chillies Scoville tested was a naga jolokia which is primarily found native in Bangladesh which he measured at 850,000-1,000,000 Scoville units.
Scoville’s name has since become closely associated with the measure of pungency (heat), but the oral test is now being slowly replaced by a modern machine (High Pressure Liquid Chromatograph) that is as sensitive as the human tongue and unlink Scovilles method numerous tests can be conducted each day.
When choosing to Grow Chilli looks at the Scoville scale and choose a chilli that will suit your tastes. My favourite is birds eye chilli but they are quite hot coming in at about 50,000-100,000 scoville units.