Changes

The next equation determines how much SMM is converted to DMS during cooling, and this amount is considered more important because it is mostly not evaporated off (especially in a closed cooling system). This equation, however, uses an average between the boiling temperature and the final chilling temperature. This model has proven to work well assuming normal brewing procedures which assume the wort is boiled, but cannot be used for wort that is not boiled. This is because the half-life of SSM is doubled for every 6°C cooler(see the [[Dimethyl_Sulfide#Mashing_and_Boiling|SMM half-life table]] above). An example will help demonstrate this issue. Suppose the wort cools from 82°C to 20°C over 60 minutes. Using the accepted set of equations that predict how much SMM is converted to DMS during cooling, first an average between the starting temperature and the final temperature is computed: <code>Average temperature = (82°C + 20°C)/2 = 51°C</code> then, using 4,000 as a constant used in the equation, a time-dependent differential equation is used: <code>Time = (60 min x 51°C)/4000 min) = 0.765</code> and finally the <code>0.382</code> number is used to determine how much SMM is left over: <code>SMM left over after cooling = 920 µg/L x 2^-0.765 = 920 µg/L x 0.588 = 541 µg/L</code> and the amount of DMS created in the wort during cooling: <code>DMS created during cooling = 920 µg/L - 541 µg/L = 379 µg/L</code> Using the exact same wort composition but with a 60 minute boil, this example in "Principles of Brewing Science: A Study of Serious Brewing Issues" computes only 92 µg/L of DMS, mostly because a lot more of the SMM is converted to DMS during boiling, leaving less SMM to convert to DMS during cooling. Even with the higher SMM during cooling in the heat pasteurized wort example, that hardly seems fair considering that the half-life of SMM is ~300 minutes at the pasteurization temperature of 82°C.