Sour Mash Procedure

by Bill Vaughan,
If you're doing a part-mash, part-extract recipe, this applies to your whole mash. If all-grain, you should probably only do this with part of your mash unless you like really sour beer.

Mash as usual. Do NOT try to sour the mash before mashing -- it will get sour but will not convert. Amylase seems not to work at low pH.

Take the mash to 170F for mash-out. At this point it contains no lactobacillus, so we will have to introduce some. There are four obvious sources: yogurt, sourdough, and "wild" lacto from grain hulls or the air. You need to cool the mash to the correct temperature for your lacto source.

  1. Yogurt: I use commercial packaged yogurt culture, from your local health food store. I suppose you could use grocery-store yogurt, but I've never tried it. Cool the mash to 90 degF, sprinkle the culture on the surface of the mash and mix it in.
  2. Sourdough: Use a commercial packaged sourdough starter, but don't just sprinkle it on your mash -- it will take too long. Instead, a week or so early (about when you do your yeast starter -- you DO do a yeast starter, don't you?) make a 1-pound mash of plain pale malt and start the sourdough starter in that. By mashing day it should be nice and stinky. Stir the whole mess into your mash. Starting and fermentation temp is about 105 degF.
  3. Wild lacto, from grain hulls: This is the traditional method. Just stir a quarter pound of grain, right from the sack, into your mash. I don't know the traditional temp, but I suspect 90-100 degF will work.
  4. Wild lacto, from the air: Cool your mash to about 90 degF, take it outside, and leave it open to the air for about twenty minutes. Shoo away the birds. In principle, this can give you a particularly local lactobacillus strain. I don't do it -- I figure my local strain is just lactobacillus sanfrancisco anyhow.

In all cases, keep the mash at your fermentation temp until it is ready. That will take one to two days for yogurt culture, maybe three days for sourdough. The only time I tried wild lacto, it was like lightning -- five or six hours.

When the stuff is done, it will look and smell spoiled. There is nothing uglier than a lactic fermentation, and your marriage may be in jeopardy from the stench. The mash will look soupy, with husks floating on top and a lot of bubbles. If you can get it past your nose, you will find that the liquid tastes good. Sour, but good.

I suppose you can let the mash ferment to completion, but I don't. It would be terribly sour. I go for my target pH, and then raise the mash back to 170 degF for sparging.

Before re-heating your mash, you should pull some out -- say a half pound to a pound -- and keep it. That way, if you like your sourmash beer, you have a ce ready-made for your next batch. It will keep for a surprisingly long time in the refrigerator, with a lid on it. Feed it every month or so. You can even make sourdough bread out of it.