Our last 4 or 5 batches have had a distinctive sour flavor to them even though each has been a completely different style (wit, brown, 2 stout, hefe).

What are the common reasons to get a sour off flavor?

Extra Info / What we have tried:

  • Extra sanitization, but either we are still missing it or thats not the problem
  • we do BIAB
  • have a consistent 64F fermenter
  • not all done with the same yeast (but it was all dry yeast)
  • the sour is not wanted..

We ordered new tubing, new siphon, new yeast (not dry) and just did a batch last night hoping one of those will fix it. Any advice?

  • 1
    At what point do you notice the sour character? Primary/secondary/bottling/bottles after 3 weeks?
    – GHP
    May 9, 2012 at 20:11
  • After bottling, when they should have been good to drink, but not just a green taste, some were a good month past bottling. May 9, 2012 at 20:44
  • does it taste like anything else you've experienced, and as well as taste, how does the beer smell?
    – mdma
    May 9, 2012 at 21:17
  • 1
    Are you fermenting in plastic or glass? Plastic, if scratched, can become a nightmare to sanitize. Buddy of mine had a similar issue, although it was apparent before bottling. It was definitely a lacto infection. Replacing his plastic primary solved the issue.
    – roto
    May 9, 2012 at 21:18
  • 2
    It tastes like we were took a sour beer (I have only had 1 that a fellow home brewer purposely made) and poured a little in, so it has a slight sour aroma along with the sour taste. We are fermenting in glass carboys, the only plastic is the siphon, tubing, and bottling bucket, and mash tun (we bottled 3 batches kegged 2) May 9, 2012 at 21:32

5 Answers 5


My understanding is that the most common cause of sour flavors is a wild yeast or bacteria infestation. In a beer that is deliberately sour, a Brettanomyces yeast strain is introduced along with bacteria to create the sour flavor.


  • Do you bake a lot in your home? It is possible that you have airborne yeasts in your home if you bake bread at all.
  • Try making a yeast starter with the dry yeast or switching to liquid yeast as you mentioned. The faster you can start your fermentation, the less time any wild or undesirable yeasts will have to take root in your beer.
  • Is it possible that you are confusing the taste for that of tart, green apples? If you are making high gravity beers, the off-flavor could be Acetaldehyde, which is produced by yeasts during fermentation but dissipates as time goes on.

To answer your question, here is a very comprehensive list of potential off-flavors in beer.

  • 2
    Brett takes some time to develop sourness. Lactobacilis or acetobacter will work faster. Starters with dry yeast is a bad idea. Pitch two packets of dry prior to making a starter.
    – brewchez
    May 9, 2012 at 23:12
  • I didn't know that about dry yeast. What is the reason for not making a starter? I have only used liquid yeasts.
    – Jordan
    May 9, 2012 at 23:19
  • 1
    I do bake a lot of bread, but they ferment in my garage in a temp controlled fridge and they usually start fermenting within the first 12-18 hours. It could possibly be a sour apple flavor :) May 10, 2012 at 13:43
  • Acetaldehyde could be the culprit. It also occurs to me that you may be tasting a vinegary or tanic flavor. Is that possible? That could be caused by oversteeping your grains during your BIAB process or using grains that are milled really finely rather than just cracked. Hope that helps!
    – Jordan
    May 10, 2012 at 14:12
  • Interesting, I don't sparge, but I do crush the grains a bit more than cracked. If fact this last batch (have not tasted it yet) I experimented by milling them twice to see if it made any difference to OG. I am going to have to read more on that. May 10, 2012 at 14:52

Do you ever notice a little layer of film in the neck of your bottles from the bad batches? That's a "pelicle" and is a sign of Brettanomyces/Pediococus/Lactobasilus activity.

For what it's worth, I am leaning towards the theory that you had a contamination in your bottling line, probably in the spigot of the bottling bucket. I've looked in some of those and see nasty things growing when not rinsed out thoroughly after each use. There's a lot of areas for stuff to hide in those spigots and its cheaper to replace them every couple of batches than to risk a whole ruined batch.

  • When I get home I will look closely for that film layer. It probably is a good idea to replace the spigot or at least take it apart and really clean each piece. I have had it for over a year now. This type of infection could explain the bottled batches, but what about the kegged? I normally skip the bottling bucket completely when kegging and just go strait from the fermenter to keg. May 10, 2012 at 19:27
  • Ahh didn't realize it was in the kegged batches too. Its probably something in your tubing line then. Throw away everything soft plastic, boil your keg O-rings, and see if it helps. Best of luck!
    – GHP
    May 11, 2012 at 18:48

"Graham's" post about "when do you notice the sour taste appear" is very important. If you don't already, next time you brew, draw a small sample at every step, if you can handle it, including your freshly cold full strength beer wort. When I was new to all grain brewing I had a batch go sour. When I went back through my notes, I had made a comment that there was a slightly sour taste after primary when I racked the beer into secondary. I was able to pint point the infection to my fridge where I had let the wort cool for 4 or 5 hours (didn't have a chiller yet)! If I had not made that comment in my log, I would have had no idea at what point the infection occur. It is strange that both your bottles and kegs are tasting sour. Although the spigot seems a likely culprit, it must be something else if the contamination has entered the keg as well.


Bacteria and yeast are actually pretty tough little critters. My brewing buddy always says once you brew a sour beer you are very likely to do it again and again without meaning too. The reason is that the nasties get into tiny imperfections (e.g. scratches, etc.) and survive even the most thorough sterilization techniques. So what we can assume is that most likely somewhere along you process you have an infection stowing away that is souring your beer. Knowing where the infection comes from would help, but how many batches do you want to ruin before figuring it out?

Seems most likely that the infection you are seeing is happening during bottling but it could happen at multiple steps in the process and there is really only one way to get rid of the problem. Throw out what you can afford to replace (e.g. tubes, stirring implements, spigots, buckets, etc.). Then for those you can't replace easily sterilize the hell out of them and sterilize for a lot longer than you normally would shaking vigorously. Times like these are good opportunities to take a look at your sterile technique and get paranoid like crazy. Clean and sterilize everything very carefully. I mean everything!

P.S. BIAB is awesome!!! Good choice of mashing techniques.


Chlorophenols are sometimes identified as having a sour taste. Is your water by any chance chlorinated? If so, do you do a anything to remove the chlorine?

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