Sour Mash Secrets

Why bother with sour mashing? Aside from mastering a new technique, the biggest advantage is that you can blend with sour mash.

Jester Goldman Aug 18, 2017 - 7 min read

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Directly adding lactic acid may get you a sour beer quickly, but a single note of lactic bite won’t offer much nuance. Fortunately, you can get more character by kettle souring or sour mashing without much additional effort. Some online sources confuse the two, but they are distinctly different processes even though they share the goal of letting Lactobacillus chomp through some of the sugars to generate tangy goodness.

Kettle or Mash?

When it comes to making quick sours, both approaches support brewing anything from a light tang of tartness to a quite assertive sourness. It’s all a question of how much Lacto is present and how much time it’s given to work.

The two differ on when the bacteria is brought into play. Kettle souring lets the Lacto loose on the wort, either starting with an extract recipe or after the mash. Sour mashing introduces the bacteria during the mash itself. In many respects, it’s more predictable to sour in the kettle: the mash is already complete, it’s easier to take a sample while minimizing exposure to the air and other bacteria, and you can taste the degree of sourness directly. Also, because the heat capacity of wort is higher than a mash, kettle souring should have easier time maintaining temperature.

Why bother with sour mashing, then? Aside from mastering a new technique, the biggest advantage is that you can blend with sour mash. A larger percentage will create a sour beer, but a small sample (under 5 percent of the grist, rested overnight) can merely drop the pH into a more optimal range for a more normal recipe. As long as the total mash pH doesn’t fall below 5.2, the final beer shouldn’t have detectable tartness. Of course, there’s a risk that the sour mash could be spoiled by undesirable bacteria or you may overshoot your target acidity.


Sour Mash Steps

Just as with kettle souring, you want to create a healthy Lactobacillus culture, protect it from infection, keep it at a healthy temperature, and give it time to work. Because you’re working with the mash, the process is slightly different, but the steps and concerns are consistent.

Mash as Usual

Sour mashing begins like any other batch of all-grain beer. Run through your regular mash schedule to convert the starches to sugar. Be sure to mash out, even if you normally skip it. The high temperature should take out any bad bacteria.

Note that if you’re just planning to acidify a normal mash, this step only applies to the sour mash portion of your grist.

Inoculate and Protect

Before you inoculate the mash, you’ll need to drop the temperature into range. Because the risk of infection is a bit higher, aim for 115-120°F (46-49°C), which will further reduce the chance of Clostridium infection.


You can inoculate with a specific culture or take advantage of the Lactobacillus that’s naturally present on the grain. A handful of grain will have all you need to get started, but it may also include acetobacter or Clostridium, either of which could ruin your beer. If you choose the grain, just mix a handful of uncrushed grain into the mash. If you go with the culture, it’s probably worthwhile to make a starter like you would with yeast before you stir it in so the bacteria can get right to work and choke off any competition.

Just as with kettle souring, you’ll need to protect your mash from oxygen and other bacteria. Purge the top of your mash tun with CO2 and then press a layer of plastic wrap into the mash, making sure that there are no bubbles. After that, go ahead and close the mash tun.

Hold Temperature and Wait

If infection is the biggest danger, holding the mash at the right temperature can be the hardest part. The same techniques for kettle sours will work well here: electric blankets, heating pads, or a sous vide device. Additionally, some people stir in hot water to raise the temperature. My only concern would be the risk of exposure to air and bacteria. If you go that route, avoid splashing when you add the water and be sure to purge the headspace again and reapply a fresh layer of plastic wrap.

Give the mash at least 8-12 hours before checking the level of sourness. A pH meter will come in handy to see if you’re in the target 3.0-3.7 range. Most likely, you’ll need to give it more time if you’re brewing a moderately sour beer.

Sparge as Normal

Once the mash is sour enough, it’s ready to sparge. When you take off the plastic wrap, give the mash a sniff. If you pick up off aromas such as vinegar, vomit, or body odor, you can try discarding the top inch or so of the mash. This is where invading bacteria are most likely to be. Removing this layer may be enough to take care of the problem. If not, you now have a better understanding of the risks of sour mashing.

Sparge and collect your wort. At this point, you can taste it and assess the sourness. If it’s more than you had hoped, you can always dilute it with some regular sweet wort. If necessary, you can even boil and then can the sour wort to save for later blending.

From Berliner Weisse to Gose and points in between, quick souring is rapidly becoming the time-constrained brewer’s choice for building pleasant tartness on a schedule. In Craft Beer & Brewing Magazine®’s online course, Quick Souring Methods, Funkwerks Cofounder Gordon Schuck explains how to use Lactobacillus bacteria, experiment with sour mashing, test acidity levels, and more. Sign up today!