Pasteurization is usually done to milk, which was first suggested by Franz von Soxhlet in 1886. There are two popular ways to pasteurize milk. First, high temperature/short time (HTST), and second, ultra-high temperature (UHT). HTST is the most common method. Milk only labeled "pasteurized" (or "past") is usually treated with the HTST method, whereas milk labelled "ultra-pasteurized" or "UHT" must be treated with the UHT method. HTST is when the milk is at a temperature of 72 degrees Celsius (or 161.5 degrees Fahrenheit) for at least 15 seconds. UHT is when the milk is at a temperature of 138 °C or 280 °F for at least two seconds. 