I've read through the various posts here and the common wisdom is that off flavors are because of poor sanitizing or using scratched plastic carboys/buckets. I'd like to read from some of the "master brewers" here and get their take on this commonly held notion.

Here is the basis for my question:

  1. Palmer's reference has very few off flavors that he mentions as a function of cleaning and none from using scratched fermenters. So, if you know that you are using proper sanitizing technique, have you still produced off flavors? If so, were you able to track down the source as something different than Palmer's observations?
  2. Another commonly held notion is that glass is better than plastic because plastic scratches and these become sources of infection and off flavors. Have you ever had this happen with scratched plastic carboys when you knew that you sanitized properly at the beginning?

2 Answers 2


Off flavors come from process issues and sanitation issues. An example of a process issue would be over-pitching or under-pitching yeast, or over oxygenating or splashing while transferring and oxidizing finished beer. Sanitation issues are off flavors from microbial infection. I would say that most of the time off flavors are generated through process issues, not sanitation issues. That is to say, its not hard to have good sanitation practices.

Knowing how to distinguish where an off flavor came from is very important. I think this is why you don't outright see Palmer's book talking about scratched fermentors. He talks about where the flavors come from. (You can get microbial infections without scratches)

That said, scratches don't guarantee microbial contamination. I understand the theories behind it, but I can't say know of too many failed batches that can be tracked to a scratched fermentor. I think the scratch thing is a bit overplayed. A deep gouge that you just can't clean out effective would give you problems. Scratches only become sources of infection if you had an infection in the last batch.

  • thanks, brew. Is it possible that off-flavors are being attributed to microbial infection when the actual source is something else? If you have run into an infected batch, what was the characteristics?
    – drj
    Oct 3, 2011 at 21:33
  • Infected batches can lead to a variety of off-flavors, from "band-aid" to "burnt electronics" to "pineapple". Lots of out-there possibilities.
    – GHP
    Oct 4, 2011 at 12:08
  • I had an infected batch on note, and it was sour in an unpleasant way. The beer had a definite paper bag quality to it as well. That beer was infected as I am pretty sure I knew the point at which I accidentally infected it. I have had batches that had too fruity a fermentation character, that was process. My most recent batch was a Baltic Porter that has a definite grass-like character to it. Which I attribute to the 2 year old pilsner malt that probably wasn't stored well. Come to find out "grass" is exactly a flavor descriptor for old malt.
    – brewchez
    Oct 4, 2011 at 14:04

I can't comment on Palmer's observations, I haven't had a plastics-related infection.

Generally, from a scratch standpoint glass is better than plastic, when it comes to using carboys as fermenters. But only from that standpoint. Plastic carboys are superior in a lot of ways, but hard to clean because you can't just go at them with a bottle brush.

Personally, I think a carboy is sub-optimal to ferment in. Age? Sure. Ferment something that doesn't krausen? Sure. But regular old beer? No.

I find plastic buckets are superior. Easier to clean, easier to handle and not slippery and dangerous like glass carboys. Soft cloth and mild soapy water to clean. Never store anything but beer in them, no matter how handy it would be to just slip your bottle capper into the bucket.

Small scratches can harbor bacteria. I'm not saying that Palmer is wrong, but I think there is anecdotal evidence to support the idea.

Here are a couple of related links to plastics on this site.

  • If sanitizing has been done properly, why would bacteria in the scratches be a problem, since they are killed? Are the bacteria that are worrisome introduced after sanitizing as part of the wort?
    – drj
    Oct 3, 2011 at 21:29
  • My understanding is that the sanitizer simply doesn't get into some of these scratches, microbubbles can form that dissipate later, exposing the beer. Can I give you scientific proof? Nope. Nor can I disprove it, which is why I don't discount it as a possible problem. I'd hate to lead anyone astray by claiming it isn't possible for scratched fermenters to be an issue and then be wrong about it.
    – TinCoyote
    Oct 3, 2011 at 21:58
  • totally understand erring on the side of caution. so scrubbing with the sanitizer would eliminate the worry about microbubbles and released bacteria. Of course, I'd think that the alcohol in the process would kill any dangerous bacteria that weren't killed during sanitizing or at least reduce the reproduction. thanks for your insights.
    – drj
    Oct 3, 2011 at 22:11

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