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?

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    I like your idea here, but don't know enough to answer your questions. Good luck and be sure to come back and leave a comment afterwards.
    – Graham
    Nov 11, 2014 at 21:10
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    Regarding the tubes (Assuming you are using a corny), I would just not put the "Liquid Out" tube in. CO2 is heavier than O2, so pushing CO2 into the "Gas In" will push the O2 up and you can let the O2 escape through the pressure release valve. Nov 12, 2014 at 8:00

1 Answer 1


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.

  • Nice comments. I might that your approach. I use rubbermaid mash tun so a good scrub and Idophor after might do the trick.
    – muck41
    Nov 20, 2014 at 20:26
  • @muck41 Remember, full-mash souring is all about experimentation. Don't be afraid to just see what happens, and don't be afraid to let things get a little funky. It's just grain and water.
    – Sneftel
    Nov 20, 2014 at 23:02
  • (And make sure to stop the souring before it tastes like you are literally drinking yogurt.)
    – Sneftel
    Nov 20, 2014 at 23:03

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