Sour Wort Berliner Weisse

Wort ready to sour

Souring wort alone can add control to your pre-boil souring process

Brewing sour beers can be a risky proposition that requires a lot of patience. The “wild” yeast and bacteria that create the sour, funky flavors we like can invade other non-funky beers if we’re not careful, and it can take time for complex flavors to evolve in the fermenter. However, there is one shortcut to a tart beer that we can take advantage of: pre-boil souring.

I’ve written previously about sour mashing, which is the technique of inoculating a mash with Lactobacillus – a bacteria responsible for souring beers – and allowing the mash to turn tart over a period of time. This method has its drawbacks. It is tricky to keep air away from the mash in the kettle. Oxygen can encourage growth of unwanted microorganisms that can contribute a “dumpster” character to the souring mash and perhaps to the final beer.

Some use a layer of plastic wrap set directly on top of the mash in the kettle to keep air away, while others purge the space above the mash with carbon dioxide. Depending on the size of your kettle, both of these can be difficult to accomplish.

After reading Michael Tonsmeire’s book, American Sour Beers: Innovative Techniques for Mixed Fermentations, I was inspired to try collecting the wort and souring it without the grain. This allows  for easier elimination of contamination by air and prevents any problems with stuck sparges.

The process for this two-gallon (7.5 liter) batch began the same as my sour worting experiments (see recipe below). I lined my kettle with a brew-in-a-bag (BIAB) bag and conducted a standard mash at 152˚F (66.6˚C) for one hour to convert starches into sugar. (My kettle was small enough to fit into my kitchen oven to help maintain the temperature.) I then added cool water to bring the mash down to 120˚F (49˚C) – the temperature that is said to make Lactobacillus happy.

My source of Lactobacillus was unmilled American 2-row. There is enough of the microorganism on the malt to do the trick. I soaked half a pound (226 g) of 2-row in the mash for half an hour to allow the inoculation to happen.

The next step was to remove the grain from the wort. This is easy when using a bag. I simply gathered the nylon bag up and lifted it out of the kettle, squeezing the bag a bit to collect as much wort as possible.

From there, the wort went into two sanitized one-gallon glass jugs . I was able to fill the jugs all the way to the top, eliminating all exposure to air. I attached stoppers and airlocks.

Wort in the smoker

An electric smoker will maintain temperatures over several days

Now, the process resumes being very similar to the sour mashing experiments. I put the two jugs into my electric smoker. This allowed me to maintain the temperature of the wort at or around 120˚F (49˚C) for the duration of the souring. After three days, I brewed.

The boil is very simple: just fifteen minutes with a small amount of hops added at the beginning. Our purpose here is mainly to sanitize the wort so that the Lactobacillus is neutralized before coming into contact with the fermenter. I recombined the content of both jugs into the kettle.

After chilling, I pitched with Safale US05 and allowed a standard fermentation.

The result is a very clean, tart, refreshing beer that is free from all potentially dumpstery off flavors. It is tasty on its own, or you can dose the beer with syrups to add a bit of sweetness and flavor. In this Basic Brewing Video episode, Steve Wilkes demonstrates how to make a blueberry and lavender syrup from scratch.

Souring the beer in the fermentation process can create a result that is more complex and interesting. However, if you’re looking for a quick, controllable way to get a tart beer, souring your wort is a quick and easy option.

Sour Wort Berliner Weisse
Two gallon (7.5 liter) batch
OG: 1.035  FG: 1.006 ABV: 3.8%

1.5 lbs (680 g) American 2-row
1 lbs (450 g) Malted Wheat
4 oz (113 g) Malted Rye
8 oz (226 g) Unmilled 2-row (for inoculation)

7 g Hallertauer hops

Safale US05 yeast


I added the milled 2-row, wheat and rye into 6 quarts (5.6 liters) of strike water at 160˚F (71˚C) to obtain a mash temperature of 152˚F (66.6˚C) that I held for an hour. After the mash rest, I added 4 quarts (3.7 liters) of room temperature water (your mileage may vary) to bring the mash down to 120˚F (49˚C). When the mash had stabilized at the new temperature, I poured in the unmilled 2-row to inoculate the mash with lactobacillus. I let it sit in the mash for 30 minutes before pulling the grain bag out and collecting the wort.

I was able to fill two one-gallon jugs to the top with no airspace. Those went into my electric smoker with airlocks added for three days. The electric smoker made it easy to maintain my 120˚F (49˚C) temperature.

Following the souring, I boiled the wort for 15 minutes, adding the hops at the beginning of that boil. Fermentation followed normally with Safale US05 yeast. I batch primed with 36 grams of dextrose. Yield: 15 bottles.


Related articles

Sour Success at Fossil Cove

A Simple Sour Beer

On Sour Beers and Sanitation


  1. Alexander Gashti says

    Instead of inoculating with grain, have you considered inoculating with pure lactobacillus culture? This may lead to more consistent beer, since you don’t really know what you’re getting on the grain from one batch to another.

    • You can certainly do that. I like using grain because I always have grain on hand. This is the third sour mash/wort beer that I have done, and the sourness has been consistent from batch to batch.

    • I haven’t been particularly impressed with the souring abilities of any commercial lactobacillus. It seems that people doing the method from this article have much better results. I made a traditional no boil Berliner Weisse and it took almost 2 months before the sour and flavor was really suitable. I don’t think that the souring you get from this method, eg the faster method, is any worse or any way inferior to using a pitch of lacto.

  2. I’ve been meaning to give this a try myself. but I haven’t had the chance yet. My thought is to hold the innoculated wort in a keg that is purged with CO2. Since I don’t have the ability to hold the souring wort hot in something like a smoker, I could just put the keg in a cooler that was partially filled with 120F water. If needed, I could boost the temp back up by adding hot water every so often.

    I heard an interview with a pro brewer recently who purges his kettle with CO2 when he brews sour wort beers. He claims that plays a large role in minimizing off flavor production during the souring phase.

  3. Thanks for the reference, James!

  4. beer looked really clear in the Basic Brewing video – how long did you let it ferment? Did it all settle or did you do anything to clarify prior to bottling? thanks!

  5. I’m doing a 100% Brett beer and wanted to give the little beasties some lactic acid to work on so I pulled a few liters of wort before transferring to my fermenter and added some probiotics to sour. The plan is to pasteurize this portion after it becomes very sour. However, it just occurred to me that I pulled it after the boil with about 11 IBUs worth of hops. With this inhibit lacto in the probiotics? Thanks!

  6. Brandon Klevence says

    How long did you let this ferment for?

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