I have had a recurring off-flavor in my ales that I would like help identifying and preventing.

The flavor is a yeasty flavor with some savory components. I have tasted it a few times in commercial beers, but usually it's less pronounced and fairly tolerable. In my homebrews, it can be overwhelming and I've even tossed a few batches because of it. Prior to fermentation (post sparge), the flavor is not there. It only appears after fermentation has started. It always accompanies an overproduction of trub, with more "floaters" than normal and more haze than normal. I can usually smell it right away, often times right after fermentation starts. It usually does not subside with bulk aging, but a few times it seems like the brew has become more tolerable after being kegged for a month or two.

It does not really match any of the typical off-flavors, but does almost have a blood-like component and sometimes a sulphur component. However, a metallic flavor ostensibly comes from metal equipment, not the fermentation, and sulfur from lagers...

I have never had this problem with sour beers, ciders or lagers, only ales, and I think always with S05, one packet for a typical SG of 1.050 - 1.060, most often rehydrated, sometimes directly pitched. I thought I had used a different yeast in the last one, but after looking at my notes, it was in fact, S05. I did buy a 6-pack of S05 a while back, so maybe the yeast was bad, but it seems like I have had this problem before I bought that pack, but maybe not as often.

Per jsolarski's comment, I did solicit some taste notes. Unfortunately, all I really got was a quick head turn, clearly noting the off flavor, but not really any good descriptions, except perhaps a bit salty. I don't pick up any salt flavors, but perhaps this comes from the savory notes.

I'll bring a growler to an event tonight with some other homebrewers and see what other tasting notes I can get.

Possibly related, What exactly is yeast-bite?

UPDATE: I had a few friends try the beer and one home brewer in particular identified it right away as Tetrahydropalmatine (THP), and he described the flavor as mousy or cheerios. I think this sounds plausible since I've described it as savory, and another as salty. According to milk the funk,

"mousy", "urine" (in high amounts) Cheerios® or Cap'n Crunch® (in low amounts), "breakfast cereal", or more generically, "cracker biscuit" flavor

Unfortunately, most of the article is with respect to sour beers, and I do not have this problem with sour beers. Also, much of the production is mentioned post-fermentation, but in my case, it is noticeable at the very start of fermentation.

There's a lot of speculation in the article, but not much that matches my experience.

This article mentions

In the presence of oxygen, Brettanomyces will produce both ETHP and ATHP from lysine and glucose or sucrose, though the exact metabolic pathway remains unknown

I'm not using brett, but perhaps S05 can do this as well?

So, given that, how do I go about preventing it?

  • can you give a better description of the off flavor, "yeasty flavor with some savory components" and "but does almost have a blood-like component and sometimes a sulphur component" do not give a good description of it.........
    – jsolarski
    Oct 24, 2018 at 22:30
  • How much yeast are you using per volume of wort? Is it dry/liquid, if it's dry are you rehydrating it? Are you oxygenating your wort and if so how? And what is your water profile like? I don't have a clue about your problem but answers to some of these might help a more knowledgeable person to debug it Oct 25, 2018 at 16:22
  • So a couple of questions - how's your sanitization? If Brett can produce it, are you sure that your equipment isn't Brett contaminated? Second, it seems like it can be produced by Maillard reactions? Are you browning your wort during the boil? Nov 17, 2018 at 1:53
  • @ChrisMacksey - Thanks. Sanitation is pretty straight forward because it is just one silicone tube from kettle to fermenter and the fermenter's had star san sitting in it, then transferred to a bucket with the air lock, lid and tube. I do a 75 minute boil, but nothing too crazy. I did an ale a few weeks ago that did NOT have this issue. The only thing I did a bit different was I used a stainless racking cane on the hot side (pre-boil).
    – Wyrmwood
    Nov 17, 2018 at 22:50
  • Are you using the same fermenter in all cases? I can't see any pre-boil equipment affecting sanitation so long as they are clean. Nov 19, 2018 at 22:43

1 Answer 1


My friend made a beer with US-05 that tasted like that, in his case the problem was he stored the yeast in the freezer for a couple days and most of it died, so the dead cells released a lot of off-flavors and the beer got very hazy.

How do I go about preventing it?

Avoid any conditions that might freeze the yeast, like purchasing yeast from online retailers during extremely cold weather, whether dry or liquid.

  • This seems very plausible, since all 5 S-05 packs were bought together, and the following ale (and subsequent ales) have not had this flavor. It could even be transport of dry yeast during cold weather, or even sitting on my porch in freezing weather.
    – Wyrmwood
    Apr 4, 2019 at 19:58
  • It would depend on the temperature but it makes sense, you can store yeast in the fridge but not in the freezer, freezing low temps will destroy cells' walls.
    – gcampos
    Apr 5, 2019 at 20:05

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