off flavor issues

[HubCity]

I am having a periodic issue with an off-flavor in my beer. It is hard to describe but almost a cross between heavy clove to almost metallic taste and a very similar aroma. So far I have had this happen 2 out of my last 15 batches. The first time it happened I thought it might have been from storing my yeast too long (it was at about 12 days). This last time it was a direct repitch with a different type of beer and a different strain of yeast (only the second pitch). I fear I am getting a contamination from somewhere but have no clue where. I just tore apart and completely cleaned my plate chiller before this last incident. The flavor usually is present within 3 days from the start of ferment. I'll gladly take any suggestions and and answer an questions that could help me pinpoint my issues. Thanks in advance.

BJ Knoke
Hub City Brewing Company
Stanley, Iowa

[kugeman]

BJ,
What kind of yeast are you using? Was the fermentation different in these two batches? The clove/metallic flavor you're describing makes me think you're creating phenols. Would you describe the flavor as medicinal, or plasticy? So your prob. could be related to fermentation temperatures. Just a thought...

[HubCity]

The fermentation was a bit slower on those batches (by one day). The fermentation temperature remained at a constant 18C in both cases. I would say that it is a medicinal taste. Chlorophenol was one of my guesses. I use no chlorine based cleaners and we use filtered well water so my guess would lead to a wild yeast. My main concern is pinpointing the source of said contamination.

[brewer2001]

How old are your hoses?

BJ,

Do you have the ability to re-attach your hose fittings?
If you do cut off a short length of each transfer hose, split it length wise and check the inside for cracks. If you suspect contamination that will be one place you might find it. You stated it showed up after you pitched from another batch (I assume had no signs of "off-flavor").

Hope this helps.

Good brewing,

Tom F.

[Moonlight]

Step one, get a new yeast culture. If there is a living creature problem, you will just be continuing the problem until you get a fresh pitch.
Irish ale, for example, frequently mutates to a creature that gives a phenolic taste. I stupidly repitched the top of my cone for a some months and inadvertently selected for the later-settling mutants. Frequently mutants have poorer settling tendencies and can often be found hanging out longer after fermentation, perhaps eating things the usual culture gave up on, and leaving phenolic flavors. They can be noticed by slower clarifying beer (sometimes slightly longer fermentations) and are therefore more likely to be found in the last-settled layer of yeast. While it's really normal to have some mutants in your culture, it is more important what per cent of your culture are mutants (also true of contaminants.) This is why it is always best to harvest the middle section of yeast for re-pitching as you select for the cells that behave the way you want.
Insufficient oxygen can hinder your culture yeast, allowing everything else to have an edge. Even something like a clogged oxy stone not creating fine enough bubbles can result in under-aeration and off-flavors. Is it possible that your yeast is not being kept cold enough? Are you using zinc or an (overkill) yeast nutrient that would provide zinc for better yeast health? Any such factor would contribute to your culture yeast losing vitality and allowing other opportunists an edge. If the off-flavors come and go, it sounds like a mixed culture that goes one way or the other depending on which is better suited to the particular circumstances of each fermentation.