I'm trying my hand at a sour mash, and was thinking about using a keg to hold the warm mash for a few days so I can purge the 02 and very lightly pressure to avoid contamination. I was thinking about placing a space heater in my fermentation chamber that can keep the keg at around 110 degrees for 2-3 days. I plan on mashing the entire grist of a new Wit recipe I created. Has anyone done this before and experienced anything to watch out for? For instance, how hard is it to clear out the intake and output tubes after this? I was planning on a long soak of Idophor after this to sanitize, would I need to take further precautions not to infect future batches? Has anyone found a different approach that would work better?
Background: I've done a few full sour-mash witbiers. I really like the effect, though it's not an everyday sort of style. Try brewing just a gallon, in case you don't like it.
In my opinion, worrying about contamination in a sour mash is sort of silly, because contamination is what sours the mash. Unless you're directly inoculating the mash with a pure lactobacillus culture, the bacteria will come from the handful of malt you add once the mash has been cooled from saccarification temperature. (Luckily witbier is supposed to be cloudy, so you don't need to worry about starch haze.)
In my experience, as long as you limit oxygen (covering the mash with plastic wrap is sufficient) and keep the temperature in the right range, acetobacter and other sorts of "not what I wanted" fermentation will not be a big concern. Remember, the historical sour-mash witbier style far predates iodophor; the reason lactic fermentation dominates in that style is because lactobacillus is fairly aggressive, and will get to work long before anything else does. The most effective way to get good results is to taste regularly (every 8 hours or so). When you do so, try not to stir up the mash. A basting bulb can help here.
As for making sure that you don't forevermore brew only sour mashes, the good news is that lactobacillus doesn't sporulate, meaning it's easy to kill. I gave my mash souring kettle a good ten minutes of boiling afterwards, and some Starsan, and didn't have any issues with souring on subsequent brews.