What in the World Is That Off-flavor?

written in brewing, science, water

After a couple of years brewing I came across one of the biggest difficulties in my brewing to date. A bold, in your face, undeniable off-flavor had plagued my (home) brewhouse. The flavor was medicinal, plastic-like, pool-like and very completely overruling. I lost three 5 gallon batches of homebrew, and this is the story of my quest to find out what was the cause.

I had never had a such a bad batch before then, and by bad I mean bad process, not bad recipe. I screwed up many a recipes before. The intensity in this flavor got me chasing a ghost for a few months. During these period, I brewed these beers:

  1. Saison
  2. Rye Smoked Porter
  3. Rye IPA
  4. Rye Smoked Porter (again)

In terms of brewing process, I made a few changes before this off-flavor appeared in my beers: Use a yeast starter, wort aeration with an aquarium pump and diffusion stone, and using yeast nutrients. These changes were correcting high-gravity beers which were coming out under-attenuated.


I first noticed the flavor on the Saison and the Smoked Porter, both of which I brewed close enough to each other that I didn’t know they both had this issue as they were fermenting.


I brewed the Rye IPA pretty much the day I found out about the off-flavor as I racked them to kegs, and so I didn’t really change anything about my equipment or process for that brew. I was pretty much sending a batch of wort to ferment, not knowing if it would have this flavor too. I went on regardless.

The quest begins

First I took the Saison and the Smoked Porter to my awesome LHBS. After tasting it there I was convinced this was not an easy thing to fix. The advice I got was to deep clean everything, and to replace racking canes or hoses that might be suspect.

I chill my wort with a plate chiller, so the output wort hose for this was suspect, as well as the chiller itself. I later replaced this hose, as well as my racking cane which had some buildup. It turns out you can’t really clean racking canes well, it’s good to replace these every 6 - 12 months or so depending on how much you brew. I also got a hose cleaning brush as I noticed some buildup in some hoses as well as in the in-line ThruMometer.

I also took the Saison and the Smoked Porter to my homebrew meetup, which includes many experienced brewers as well as a BJCP judge. The obvious flavor was there, everyone agreed, but nobody could tell me definitively where the flavor came from. I got conflicting advice in that some folks assured me it wasn’t a bacterial or infection induced flavor as those tend to turn beer acidic. So indeed, the plot thickens.

At this point I brewed a 2 gallon batch with the purpose of isolating the problem by chilling half of it with my plate chiller, and the othe half in an ice bath. I made a simple Pale Ale with extract, used some hops I had lying around and pitched some dry yeast. The entire purpose was not to make great beer, but rather to see if the chiller, hoses or inline thermometer had anything to do with it. It produced drinkable beer nevertheless.


Next up, I kegged my Rye IPA, and I was surprised and relieved that it didn’t have the off-flavor too. This was one of those beers that went fast because it was so darn delicious!

Confident in the fact that there was nothing wrong with my equipment at this point, I went on to brew my Rye Smoked Porter again. At this point, I had deep-cleaned all of my equipment, replaced suspect parts, and knew that it was clean of any bacteria. After all, the previous Rye IPA brew went just fine, and so did the experiment extract batch.

This time around, I tried my wort/beer every step of the way, too. No signs of this flavor on brewday, so pitched my starter yeast, and off to primary fermentation it goes.

I sampled the fermenting beer 3 days in and it was clean. Five days in, same thing. I’m safe, I thought. I let it ferment all the way, for about 14 days, and to my surprise the flavor was back when I kegged.

I still carbonated it. Before I poured this batch down the drain, I saved a few bottles to get more help identifying what’s up. I gave a bottle to a local friendly brewery, Cleophus Quealy, who also asked me for the recipe and brewing notes.

Brewing notes included the usual brewday notes, but most notably noted I used my local tap water, but removed chlorine with campden tablets, something that I’ve done successfuly in brews past.

Here’s what Peter from Cleophus Quealy had to say:

Strong antiseptic flavor. The phenols in the smoke are mixing crazy with possibly the chlorine in the water. I would ditch the campden tables and go to carbon filtering. Pretty hard to diagnose with that strong off flavor. Biggest guess is chlorophenols esp with the smoked malts.


Yeah, chlorophenols. These nasty compounds are formed when phenols bond with chlorine. Phenol production is evident in some malts and yeasts, notably smoked malts and some yeasts such as the delicious WY3711 used here among many others, but not really on WLP001 used for the Rye IPA.

Alright, so this makes sense, but does this mean that campden tablets don’t work? No, it doesn’t, and here’s the last piece of the puzzle: I started getting these off-flavors when I changed something about my brewing process, and the key lies within the yeast starter. I was just using tap water with no filtration or treatment to brew my starters. Even though we’re just talking less than a couple of liters of water, this seams to fit the bill.


I’ve since switched to using RO or carbon-filtered water for my starters, and haven’t had a problem again, even after brewing the same recipes pressumably containing the same phenol production.

Lessons and Conclusions

  • Do not mess with Chlorine. I still trust campden tablets, but carbon filtration, reverse osmosis and distillation are also effective.
  • Beware of your yeast starter water! It can ruin a batch or three.
  • Good cleaning and sanitation practices are crucial. I always thought I did a good job at this, but in the face of this issue I wasn’t sure - there was always a chance I was messing something up. As a result, I am now even more thorough about cleaning and sanitation, and going forward an off-flavor will be less likely to be sanitation related and might lead me to finding the cause faster.