jtoots said:
Does anyone have input as to whether DMS etc. is being kicked off by the wort before the boil actually starts?
As long as the wort is over 140F, DMS is coming from the SMM in the pale malt. Up to a point, anyway.
DMS boils off rather easily, since it's volatile way below boiling.
The amount of DMS in wort depends on a few easily controlled factors.
The first is when you call the beginning of your boil. Is it as the hot break happens? After?
Second, are you doing a full 60 to 90 minute boil?
The amount of DMS in wort is reduced by 50% in the first 30 minutes of a properly vigorous boil. At 90 minutes, even the palest Pilsner malt wort has little SMM left to convert to DMS and doesn't meet the threshold of perception in most people.
A proper boil is active bubbles coming up through the wort that move around the kettle. It doesn't have to be a huge, roiling, angry cauldron to effectively remove DMS.
So, keeping a lid on, or partially covering the kettle before the boil is fine. Any DMS that falls in will be boiled off again.
After a 90 minute boil, DMS doesn't rise more than 10% in 60 minutes and that's low enough to be scrubbed out by normal fermentation.