First Potentially Infected Beer

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New Member
Nov 5, 2018
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I am new to home brewing with 2 successful batches under my belt. I recently brewed a Neapolitan Stout kit from MoreBeer ( - KT HERE:

Before I put the cocoa nibs, strawberry, and vanilla beans into secondary, I tasted the beer, and it tasted a bit sour. I went ahead and added my ingredients and let it go for another 2 weeks (4 weeks total). I tasted it yesterday, and again, got a sour flavor, but the beer visibly looked ok. I went ahead and kegged it. I fear that the sourness may have been caused by fruit flies. During week 2, I opened the door to my stand-up freezer (temperature controlled, it was set at 68 degrees) and noticed 4 or 5 fruit flies flying around inside the freezer. The lid on the MiniBrew is not air tight, so I am wondering if a fly or 2 may have gotten inside?

I know from lurking in the forums that I don't need to throw it out just yet, and I need to let it hang out for a bit, so I'll let it keg condition for another couple of weeks.

My fear is that, if it is in fact infected, I've read that I need to toss out my plastics. My concern with that is my fermenter. I have a 15 gallon MiniBrew conical fermenter, so unlike a bucket, that would be a pretty expensive loss. Will it be safe if I do a bleach/hot water soak, followed by PBW, a good long rinse, and then finally an overnight soak in Starsan? I also plan to disassembly the racking port valve and the trub valve and let them soak.

Do I need to also throw out my transfer hose and the hose and diffuser stone combo for my keg lid?

I know there are probably a million of these posts on here, and I've read various things. I'm mainly just concerned about my conical and couldn't find a definitive answer. I don't want to keep ruining beer, but I also don't want to throw out a pricey piece of equipment.


Well-Known Member
Jul 11, 2011
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New Bern
There is a lot of debate about whether infected plastic can be sufficiently cleaned and sanitized. Apparently, some can be removed and some can't. In this thread Island Lizard describes a cleaning routine he uses that involves bleach, followed by several days exposure to the sun to remove the bleach that the plastic soaked up. (Any bleach remaining will ruin any beer fermented in it.) Since you have an expensive fermenter, it' probably worth trying.


Bringing Sour Back
Jan 26, 2017
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Strawberries could easily add a sour taste.

It's a good idea to stick with simple recipes add a beginner so you can diagnose problems and work to improve your process.

I would just continue as normal with everything unless it's an obvious contamination.
Take things apart. PBW soak. No-rinse sanitizer before use.


Well-Known Member
Nov 25, 2013
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If it's any comfort, it's most likely not the fruit flies causing a sour flavor. Lacto bacteria are what create sour beers. Fruit flies carry acetobacter, which is different and turns your beer to vinegar. The nibs, strawberries and vanilla beans could carry lacto if they weren't sanitized by temperature or alcohol first. Either way, it won't hurt to wait a bit more.. Give it some time and see what happens.


Progressive Brewing
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Jan 9, 2013
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Pasadena, MD
Welcome to the forum and sorry to hear about your possible encounter with an unfortunate infection.

As said before, the sourness could be from the strawberries, once the fruit's sugars ferment out, the leftover pulp is quite sour.

What kind of secondary vessels are you using? Do you see a white haze or white skin-like formation (pellicle) forming on top?

Using secondaries can cause infections (and oxidation), they're generally not needed. You can easily add fruit to your "primary" (one and only) fermenter.

Did you soak the vanilla and nibs in an alcoholic liquid for a few days to 2 weeks? Or added them raw? They could have brought in an infection too.

I've tasted a few (unintentional) sour stouts over the years, and must say they can taste pretty good. If it's a bit too sour, you could always add another (sweet) stout, some sugar syrup, or (pre-dissolved) lactose to some of the sour one in the glass. Blend to taste.

As @ncbrewer mentioned, I've successfully cleaned dirty or potentially infected plastic fermentors (buckets), as outlined in that link.

When cleaning in general, pay special attention to any rough areas, burrs, scratches, tight spaces such as rims, grooves, seams, bulkheads, valves, ports, threads, etc.

Instead of Chlorine (and UV), a caustic followed by a rinse and an acid are often used in breweries to not only sanitize (Stainless) equipment, but also thermoplastic hoses.