oxidation or off-flavor?

Hi guys I am tasting my second batch, and am detecting a slight off-flavor. Heres the rundown:

The first bottle I tried was the half-filled one (the last one filled during bottling) and it was pretty good, which was encouraging. It was exactly 3 weeks old in the bottle.

The second and third bottle a couple days later seemed undercarb'd but flavor was good.

The fourth bottle last night (now 4 weeks old in the bottle) still seemed a bit undercarbed, had little to no head, and I detected a slight "off-taste". My wife said it tasted "dirty". I thought it tasted good up front, but had a funny taste in the finish. To which she agreed.

I've never tasted oxidation before but worry that this taste (could be the power of suggestion but reminds me of cardboard) means at least this bottle or more could have oxidized, but I don't understand how or why?!

Here's what I did:
It sat in the primary almost 3 weeks and cleared fairly well. Then I bottled, using my bottle wand of course. I didn't even transfer to a bottling bucket since my primary has a spigot, and I primed with carbtabs. I stopped and capped the bottles with each 12 or so.

I don't see how I could have gotten oxidation in this batch. Was it bad the bottles got shook around once bottled? Could that have done it? Man. I got like 46 bottles of this brew and hope its not oxidation since that doesnt age out.

I am sampling another today; unfortunately the same off-flavor is there.

I'm not so sure it is oxidation, now that I've read those flavors take time to develop and worsen. My wife said she tasted iron, it reminded her of like when you accidently taste blood, and you can taste the high amount of iron in it.

Now I'm really confused. I used a SS boiling pot and platic stirring spoon. I used filtered water from my fridge for the boil, and gallon grocery store spring water to top the fermentor off, so I'm not sure how iron could be present enough to impart a distinct flavor. Besides, this flavor wasnt present in previous brews, even when sampled young.

It doesn't sound like oxidation. What was your fermentation temperature like?

Is it a big beer? Sounds like maybe they are kind of green. MOst beers improve with age to a certian point until they peak. Maybe it could be because they aren't fully carbed yet they don't taste 'right'. Am I correct in assuming the first beer you tried was fully carbed and tasted better? I say put a few in the fridge for a week or so and see if they improve. 4 weeks in the bottle should be enough time but you could leave them longer as well depending on how big the beer is. You'd be suprised at how much carbonation pulls all the flavors together. Some beers tastes golden right out of the primary and others taste like doo-doo right up until fully conditioned and carbed.

Gordie said:

It doesn't sound like oxidation. What was your fermentation temperature like?

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I kept the house in the low 70s during fermentation. I used S-05 yeast and didn't experience a furious fermentation, so I'm thinking internal temps were around 75 or so.

This isn't a big beer, just a 6 lb dme pale ale. I'm a little relieved that its likely not oxidation, hopefully this will age out in time.

On more than 1 occasion I thought I had oxidized brew, but it turned out being the flavor from the hops I used. Allow it to age longer.

I had posted something similar on here, i also have gotten that "dirt" aftertaste in my homebrews and can't seem to pinpoint what it's from.

goodbyebluesky82 said:

I kept the house in the low 70s during fermentation. I used S-05 yeast and didn't experience a furious fermentation, so I'm thinking internal temps were around 75 or so.

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I have found that US-05 (and S-04) can have off flavors at those temps.

homebrewer_99 said:

On more than 1 occasion I thought I had oxidized brew, but it turned out being the flavor from the hops I used. Allow it to age longer.

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Once again I agree with Bill here. I have had some hops give off a metallic hint for a while in the conditioning process. Coriander too. Both flavors aged out perfectly.

Any rust spots on any of your equipment? What cleanser do you use for your bottles. Most can leave residue easier than you would expect if you do not rinse very thoroughly.

You might find that a few more weeks gives the yeast time to convert some of whatever is giving those off-flavors, and it will probably taste very good after that. Sounds like your process is good.