13,701
edits
Changes
→DMS Prediction Models
===DMS Prediction Models===
Equations have been established for estimating how much DMS will be converted from SMM during boiling, and how much SMM will be converted to DMS during cooling the wort after the boil. These equations are well explained in [http://www.amazon.com/Principles-Brewing-Science-Serious-Issues/dp/0937381748 "Principles of Brewing Science: A Study of Serious Brewing Issues", by George Fix, 1999, Pgs 89-93]. One thing to keep in mind is that the equations assume "typical" brewing practices, which include boiling the wort at some point. Because of this, the equation for how much SMM is converted to DMS during cooling may not reflect no-boil wort accurately. Let's look at some examples of the equations from "Principles of Brewing Science: A Study of Serious Brewing Issues":
===Traditional Model===
First let's look at an example that should accurately predict how much SMM is in a given batch of wort, and how much of that SMM is converted during an 82°C no-boil pasteurization rest at 15 minutes. Assuming a given pilsner malt has 6 µg of SMM per gram, and the malt concentration is 200 g/L, the SMM content can be calculated:
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 which is volatilized, leaving less SMM to convert to DMS during cooling. Even with the higher SMM during cooling in our 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.
===Using Just Half-Life===
If instead we just use the first equation that predicted how much SMM is decomposed into DMS during the heat pasteurization time, we get a different value of DMS. Using this equation might be more accurate for no-boil wort since it uses the half-life directly instead of averaging out the starting and ending temperatures. We'll use 95 minutes as our time (35 minutes for heating and pasteurizing, 60 minutes for cooling):
<code>
SMM into the fermenter = 1,000 µg/L x 2<sup>-(45 min/300 min)</sup> = 1,000 x 2<sup>-0.15</sup> = 1,000 x 0.9 = 900 µg/L
</code>
<code>
DMS into the fermenter = 1,000 µg/L - 900 µg/L = 100 µg/L
</code>
<code>
SMM into the fermenter = 1,000 µg/L x 2<sup>-(45 min/600 min)</sup> = 1,000 x 2<sup>-0.075</sup> = 1,000 x 0.95 = 950 µg/L
</code>
<code>
DMS into the fermenter = 1,000 µg/L - 900 µg/L = 50 µg/L
</code>