Mash Out!—How do I make a kettle sour?

Tony Creech asks how do I make a kettle sour?

Kettle sours are quite popular right now, especially the fruited versions. Making a kettle sour may seem a bit daunting but it’s really not that difficult. You may need to pick up a heat belt, but you likely have all the equipment that you need to make one.

What you’re going to need:

  • Your typical Homebrew setup
  • A source of lactobacillus
  • A pH meter
  • Lactic acid
  • A method of keeping your brew kettle at 100°F for 24 hours

Step One: Make your wort.

Using your Homebrew setup, make a 5 gallon batch of wort. It could be any type of wort. Dark, Red, Blonde, whatever. It doesn’t matter what malt you use or how you produce it, however, do not introduce any hops to the mash or wort. Not yet anyway. The hops will prevent your wort from souring.

Step Two: Boil your wort.

Yes, this is going to be a sour beer but you don’t just want any old bacteria in there, so you want to boil your wort. Bring it to a boil for 10-15 minutes. While the wort is boiling, sanitize your chiller. If you’re using an immersion chiller (which works great for this application) just stick it in the wort as it boils.

Step Three: Cool your wort. But not all the way.

Once your wort has boiled for 10-15 minutes, you can chill it to 100°F.

Step Four: Pre-acidify your wort.

Add some lactic acid to pre-acidify the wort to a pH of 4.5 or lower. This helps prevent any unwanted microbes from growing in your wort. You’ll want to use Beer Smith or another brewing software to help you determine how much acid to add and you’ll want to use a pH meter to measure this. Also please wear gloves when handling acid.

Step Five: Pitch your Lacto.

You can use a strain that you purchased from your local home brew shop, or you can use yogurt. It’s up to you. I use Greek Gods plain yogurt (you can use any yogurt that has active cultures in it). It gives me good results and it’s cheap. After your wort has cooled to 100°F and you’ve pre-acidified it, just dump in a half a cup of the greek yogurt (or the lacto strain that you bought from your LHBS). The next step is the hardest part.

Step Six: Keep your wort all warm and cozy.

Cover and keep your wort at 100°F. This is where you may need a heat belt. You need to keep the wort at 100°F for 24 hours or until it has stopped souring. I use my Robobrew. It’s super easy to program the temp and just let it do its thing. You could use a heat belt or a fermentation chamber with some heat source. BE CAREFUL.

Kind of like how yeast can create and environment that is too alcoholic for it to survive, lactobacillus will create an environment that is too acidic for it to work in, so you don’t need to stress about it too much. You’re aiming for a pH of around 3.2, so check it around 12 hours, then 18 hours, 24 hours etc until it has reached a stable pH.

It is also recommended by most that you try to remove as much oxygen as you can from the kettle as the wort is souring. This is thought to prevent aerobic contaminants. While it is difficult to remove ALL the oxygen, flushing the kettle with is better than nothing.

Step Seven: Boil your wort. Again.

Once your wort has reached a stable ph, boil it. You’ll want to boil it for as long as necessary to reduce your wort to the appropriate volume and gravity.

At this point, theoretically, you could add hops, however, bitter and sour tend not to play well together, so I recommend saving those hops for whirlpool or dry hop additions.

Step Eight: Cool your wort. Again. All the way to pitching temp this time.

We’re almost done. Cool your wort down to normal yeast pitching temp. Check the manufacturer’s suggested temps, then once your wort has cooled enough…

Step Nine: Transfer your wort to a fermenter and pitch your yeast.

Transfer the soured, cooled wort to a fermenter and pitch your preferred yeast strain.

Step Ten: Ferment your wort.

Let the yeast do its thing. This is really just like a regular beer, just keep your wort at a consistent, desirable temperature and wait. If you want to dry hop it, this is the time to do it. Once the beer has reached terminal gravity, cold crash and package as usual.

What about adding fruit to my beer?

I’d recommend letting your beer ferment out then transferring to a fermenter with fruit in it. Boil a pot of water on the stove then carefully dunk your fruit into the hot water for a minute or two. Remove it, allowing it to cool, and then add it to a fermenter with a large opening. It can be a real pain to try to fish fruit out of a carboy’s narrow opening. Let the fruit sit in the beer for a week then check your gravity. After you’ve had a consistent gravity reading for three days in a row, cold crash it and package it up.

Have you made a kettle sour before? Fruited, dry-hopped or regular? How did it turn out?

If you have any questions that you’d like answered in an upcoming Mash Out!, please email me at

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