Sour Mash Sour Beers and a Recipe

Do you want to make a sour beer but don’t want to worry about contaminating all of your equipment with spoiler microbes?  The sour mashing technique might be for you, even if you are an extract brewer.  In a nutshell, the wort is allowed to sour during the mash, then the beer is boiled, killing any spoiler microbes before they can get to the rest of your equipment.

I heard about this technique on an episode of Basic Brewing (video 31 Oct 2012 and radio 26 July 2012), who heard it from Sean Coates, who heard it about it on the Jamil Show.  The Basic Brewing video segment details a small craft brewery using this technique to brew a sour beer on a much larger scale.  For my first attempt, I brewed up a two gallon batch of a moderate gravity ale (see recipe and tasting notes below).  The technique seems to have been pioneered as an easy way for home brewers to reproduce the Berliner weisse style, but I plan to try it for a sour porter or perhaps a tart fruity IPA at some point.

The procedure is simple.  Mash your grains as usual, then let it cool to 100-120F/ 38-48C either over time, or with cold water or ice (it will take quite a bit of cold water, so ice might work better if you are pressed for time and can’t wait).  Depending on how you are going to hold your souring temperature, you may need to do a very thick mash initially, or plan for no sparging.  Once the mash has cooled, add some un-milled grain; using un-milled keeps starches from getting into your beer and causing haze and digestive issues.  This grain is your starter culture: the husks harbor the lactic acid producing microorganisms which will sour the mash and eventually the beer .  Milled or not, it likely won’t convert, so you can leave this grain out of your OG calculations.

I used only 2 oz/ 57 g in my 2 gal/ 7.6 L batch, so it took quite a long time to sour, about 4 days.  Sean uses 1 lb/ 0.45 kg in his 5 gal/ 19 L batch (3.2 times my grain amount per volume of wort); I suspect this is closer to where you want to be.  If you are an extract brewer, I think you could dissolve your extract in some water, bring it to souring temperature, and add the un-milled grain, though I have not actually heard of this being done.

sour mash in smoker

Sour mash being held at temperature in a smoker.

After the grain is stirred into the mash, you’ll need to protect it from oxygen as best as you can.  I recommend using a layer of saran wrap (plastic cling wrap) directly on the surface of the liquid.  Some prefer to “blanket” with CO2 and cover, but diffusion will quickly cause this pocket of gas to equalize with its surroundings and let in oxygen.  The cover would need to be completely  air tight to maintain such a blanket without CO2 being actively generated (like during a strong fermentation).  Acetic acid producing bacteria, mold, and other undesirables generally need oxygen to thrive, while the lactic acid producing bacteria we want are anaerobic (do not need oxygen for their metabolism).  Due to the acid production, if you are using a pot to mash I would recommend stainless steel or ceramic coated.  Normally aluminum, copper, or other reactive metals are fine in brewing, but the acid, over such an extended period, might damage these pots and leach metal into the wort (which the yeast will generally clean up anyways, but better safe than sorry).

You’ll now need to hold the souring temperature over the course of two to four days.  I was able to fit my 4 gallon stainless mash pot into my electric smoker and set it to hold temperature.  Some ovens will also work, but most are unable to be set so low.  If you don’t have a smoker or proper oven, you can always mash in a well insulated container and use boiling water to bring the temperature up a few times a day.  It is in this scenario where a thick mash comes in handy, so you do not end up with too much water in the wort.  If you are adding water to keep temperature, you will likely not be able to brew anything particularly high gravity.  You need not fret about staying exactly on target with the temperature, but you should do your best to stay in the ball park.  Never approach 140F/ 60C, as this will pasteurize the mash.

Next comes the only hard part of the process.  After the first 24 hours, you should taste the mash about every 8 hours or so to test for sourness.  Keep in mind the sugar in the wort will ferment out later, so the post-fermented product will be considerably more sour than what you are tasting.  If you managed to keep out most of the oxygen, it will smell like something your body does not want in it, and your brain will fight you when you try to taste the wort.  I managed to get old sock, gym bag, rotten vegetable, and just the slightest hint of vomit out of mine.  But, it smells far worse than it tastes- its mostly sweet and old cooked corn with a bit of tart as it ages.  If you didn’t do such a great job of keeping out oxygen, I have heard it is considerably less pleasant.

You may notice along the way that there is some mold or other goodies growing in the pot, though I did not run into this problem having covered the surface with cling wrap (mold is a surface phenomenon).  Just scoop it off and you should be good to go.  However, I cannot personally vouch for the harmlessness of every microorganism which might be present.  I have never heard of someone getting sick from sour mashing,  but proceed at your own risk, especially if you are immune-compromised.  I tend to believe it is safe so long as the mash begins to sour relatively quickly, as most organisms which can make you sick generally do not grow in acidic conditions, and this is the way that foods have been pickled and preserved for thousands of years.  But again, I am no expert in any sort of illness and can make no guarantee of its safety.

When it has hit a level of tartness you are happy with- probably after two or three days- run off your mash, pour it through a brew-in-a-bag bag, or use whatever other method you like, and finish your brew as normal.  Sean notes in his blog post that his boils usually foam up like crazy so be on the lookout, but I didn’t notice any more foam than normal, even with a grain bill relatively heavy in wheat and rye.  After boiling and fermenting, all the nasty aromas and flavors will disappear, yielding a beer with that classic yogurty lactic twang.

[2014.02.06 UPDATE: In the 3 Feb 2014 episode of Brew Strong, they mention acidifying the mash to pH 4.5 after the saccrification rest, right before adding the whole grain kernels.  In conjunction with keeping oxygen out, this will help to limit the possibility of other undesirable bugs taking hold and avoiding some of the risk of purely wild fermentations, including some of the bad funky flavors.  An alternate method is to mash, pasteurize, cool, pitch a good lacto culture, then go on with the boil after a day or two.  This kills most everything on the grain/ in the mash and ensures the bugs left are only those added.  This still maintains the advantage of not contaminating the rest of your equipment, and is a nice compromise method.]

[2014.08.20 UPDATE: I’ve since soured (har har har) on using this method.  After some reflection, its a fun experiment, I just don’t think this is the route to the best sour beer possible.  If you really want to do a wild fermentation, a method detailed over at Ryan Brews seems to have promise (though I have yet to try it).  Otherwise, doing a primary fermentation with a known good culture of mixed microbes is probably the best route.]

Batch Size: 2 gal/ 7.6 L

2 lb/ 0.9 kg     2-row malt
1 lb/ 0.45 kg   Rye malt
1 lb/ 0.45 kg   Wheat malt
2 oz/ 57 g       reserved from above mix for souring

0.5 oz/ 14 g    Hallertau, 3.9%, 30 min, 5.7 IBU
Total IBU:       5.7 (Tinseth)

~0.8 pkt            Safale US-05 (0.5 pkt rec.)

Target CO2:     3 volumes

OG:                 1.055 (77% mash eff; target 1.043, 60%)
FG:                  1.011
ABV:                6.25% after conditioning

Mash temp:          153F/ 67.2C (target 152F/ 66.7C)
Mash thickness:   1.5 qt/lb/ 3.12 L/kg
Single infusion mash, rinsed bag of grains in sparge water
Boil time:              30 min

Calculated Profile:

Calcium 50.2 Sulfate 65 Hardness 126
Magnesium 0.1 Chloride 104.6 Alkalinity 31
Sodium 73.8 Bicarbonate 37.3 RA -5

I was pretty happy with this water profile, save for the sodium content, which is just how my water is served up.  I pulled up the chloride over sulfate to balance for a malty beer since there are only token hops in this recipe, and made sure the RA was low as its a lighter beer.  A lower RA will also help the souring along by neutralizing much of the alkaline buffering compounds. (See my water treatment post here.)

Fermentation Temperature: 70F/ 21.1C ambient; pitched at 66F/ 18.9C; lamp to keep warm as the ferment tapered

Tasting Notes:

sour mash sour beer

Sour mash beer. Its a bit cloudy because of the BIAB technique and the wheat and rye in the grain bill.

Aroma: sour orange

Appearance: about straw color, but more whitish from the strong haze; pours with light white fast dissipating head

Taste: yogurt/cider tartness with some sour citrus or orange; bit of lingering lactic acid; no hop character or bitterness detectable; slightest hint of possible corn/ vegetal taste as it nears room temperature and de-carbonates quite a bit

Mouthfeel: moderate-high carbonation, surprisingly smooth and satisfying for such moderate gravity, almost slick- probably the contribution of the rye

Overall: I am surprised by how smooth this beer goes down.  This was a great proof of concept beer, but not a recipe I would make again.  Its good, just not special.  I will definitely be using this technique again, though- I think a sour porter or tart fruity IPA would be great.  I might also try something closer to an actual berliner weiss style; this batch ended up way too high gravity after getting much higher than expected efficiencies.  I will use much more grain for the souring addition next time as well, as it took four days for this beer to sour.  [2013.11.01 UPDATE: The more I drink this beer, the more it grows on me.  I guarantee it wouldn’t hold a candle to the world’s best sours, but its simple and delicious.]

– Dennis,
Life, Fermented


About Dennis
Home brewer, home chef, garage tinkerer. Author of Life Fermented blog.

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