This question's answer led me to http://www.milkthefunk.com which is a great source of information.
Since there's a few methods for making sour beer, I should mention I've been doing what some call a kettle sour (or fast sour) where I do a mash, then a full boil, then sour the beer using l plantarum in a sealed keg purged with CO2, then do another full boil (topping up with water) then ferment as a standard ale, then keg for carbonation.
One of the issues I've had with sour beer is DMS, really with any pilsner as well. (This is why I am now doing a full boil before kettle souring.) It turns out, there are some reasons for it, as according to the article on DMS
For one, I'm boiling at 6500 ft elevation, so my boiling temp is ~199F/93C (instead of 212F/100C)
It has long been reported that the half-life of SMM doubles for every 6°C cooler, meaning that at 95°C the half-life is ~70 minutes
And two, especially important for sour beers
pH plays a role in the reduction of SMM to DMS, with a higher pH reducing the half-life of SMM
Meaning I really need to be boiling for >2 hours to be rid of DMS for an ale! For a sour, the pH may be in the 3.4 range, where SMM half-life is now 142 at 200F/94C.
Empirically, I've been having good success with a 75 minute boil for a standard ale. My ales do not have significant DMS with that boil time.
Does this mean I need a 284 minute (nearly 5 hour) boil for a sour beer at elevation to remove DMS!?!?!? (I am doubling the half-life after adjusting for both temperature (elevation) and acidity (pH).) If I do a full boil before souring, and a full boil after souring, do these add together? Or, not really, since each boil went above 80C, each boil needs to be figured independently?
Lastly, the question this has been leading up to, after the kettle sour portion is finished, can I raise pH to 5.2 using Calcium Carbonate to increase the DMS boil-off without altering the taste? Or will that kill the "sourness" by reducing the acidity?