What does oxidized beer taste like?

There's always a story before a question like that. Shortly before Labor day weekend, I went to go fill up two growlers from my kegerator only to find no beer was running. Thinking the beer line froze, I check the lines and all is well on that front but my CO2 tank is empty. The day before I was adjusting the carb levels in the keg because they were too high and the release valve must have got caught slightly open. I'm obviously bummed because I was bringing my Scottish Ale to share with some friends. It was too late to go get a new bottle of CO2 and I was leaving in a few hours. So I re-checked the release valve and then left.

Now that I'm back and I got a new tank, the beer is off. It's darkened considerably from a reddish brown to a dark brown (almost black) and while bitter is not the correct term, "sharp" is probably more dead on. And while I don't have the original and final gravity figures, it tastes almost like the alcohol content has increased. It wasn't a great beer to begin with (fermented too high with a Scottish strain) but it was at least drinkable. Now- not so much (though it does make a great marinade).

Has the beer oxidized? Is there a problem with leaving it in the keg without a CO2 cover? I would have to imagine that CO2 head bled out as well.

Sounds like you have a few things possibly going on there. Your comment about "alcohol increased" has me thinking you are tasting fusel alcohols. That is common with a high ferment temp (and also if you underpitch). Unfortunately it won't ever go away...

Oxidation is distinctive wet cardboard and sharp. I hate it. I can smell/taste oxidation from a mile away so it instantly spoils many beers for me.

I'm not sure why you think it got exposed to air? Even if your C02 purged from the keg, wasn't the keg sealed? It shouldn't have gotten significant air exposure.

Keg remained seal and shouldn't have been exposed. The only thing I can think of if the release valve was opened enough for CO2 to escape, it was opened enough for O2 to get in once the CO2 was gone (i.e. it's a bad valve - I'll know more tonight when I check the new tank). I wouldn't say it tastes/smells like wet cardboard but sharp is definitely the word I would use. As for the fusel alcohols, it's possible but what happened to the fruity esters that were there before? Is it simply the beer aging/maturing?

It could be that it warmed up? You will taste harsher alcohol with it being warm. If you are drinking a high gravity beer fairly fresh it will be very harsh, when I made an 80gp scotch ale it took about 4 months before it got drinkable and about a year before it started to get REALLY good. Not that you should wait that long, I sort of forgot about it and went back and bam, it was excellent.

I don't know the cause of the flavor issue, besides what everyone else has already said, but I wanted to mention some additional "flavors" you can get from oxidation. In early stages, oxidation can present as more of a "feel" on the sides of the tongue. It is not quite metallic, and just a bit astringent, on both sides of the tongue. As the beer ages, it can start to taste like sherry (that's called "madierized") and change color a bit. When oxidized beer gets older and through those two stages, then it can taste stale and like wet cardboard. So, oxidized beer doesn't always taste like wet cardboard unless it's terribly severe. Sometimes it's just sherry-like.

I don't think it warmed up at all - There was still a nice layer of ice on the cooling panel in the kegerator. As for aging, the beer could definitely benefited from aging but it was at least drinkable. Now, it's a completely different beer in taste, appearance, and feel.

It was in the primary for a week and secondary for two. Is it possible that fermentation wasn't done and the yeast have continued to churn in the keg? (now I really wish I would have captured the gravity) I would think it was too cold for that to happen.

I've never tasted sherry before but I might try it tonight for a comparison. I'll admit that vinegar was one of the words going through my mind when I pulled my last draft. But I'm also sure it's partly me jumping to conclusions as a newbie brewer. My taste buds are a bit askew anyways. I absolutely love Alba's Scot's pine ale and find it quite refreshing but all my friends and family say it's like drinking pine sol.

You could easily aerate your last one or two bottles from yournext batch. Mark them. And then compare differences to get a feel for what oxidized beer is like. I did this a couple batches ago just to see if I could tell the difference. It can range from subtle to really wet cardboard blandness. Try different amounts of aeration to see.

I'm kegging, but I might just rinse some bottles for a little science experiment on my next batch.

Co2 is heavier that O2. Your CO2 will blanket that beer as long as you didn't move it around too much.

nod, but wouldn't it escape from the keg if given the chance?

What would force it out if air is lighter than CO2?

Doh! You're right - I should have known better.

It will eventually diffuse into the air, however, as the air concentration of CO2 is so low that any one molecule escaping will almost certainly not be replaced. But that will take long time.

Or, to put it another way: The molecules of a fluid or gaseous substance above zero Kelvin move in such a way that each molecule has a net movement in a random direction. And a molecule that goes upward will most of the time not go straight downward again, giving it a net lift. Etc.

Not that I can follow the molecular science above, but assuming this beer was carbonated you'd also be releasing CO2 from the beer once the headspace was depressurized - oxygen isn't going to get in. Not sure on the change in flavor, could be you let it sit a few days and some sediment dropped and you got a glass full of that (would account for the change in color as well).

bruin_ale said:

Not that I can follow the molecular science above, but assuming this beer was carbonated you'd also be releasing CO2 from the beer once the headspace was depressurized - oxygen isn't going to get in. Not sure on the change in flavor, could be you let it sit a few days and some sediment dropped and you got a glass full of that (would account for the change in color as well).

Click to expand...

It's a very simple concept (though the math involved is surprisingly complex - interestingly work on this is what gave Einstein his inital fame, calculating the movement of pollen on the water surface [Brownian motion] by assuming that water was made up from nanoscopic particules in constant motion, though the concept was widely known since at least Maxwell, probably as far back as Pascal or even Democritus). This Wikipedia image is useful: http://upload.wikimedia.org/wikipedia/commons/a/ad/Diffusion_(1).png
An area with an abundant amount of one gas will tend to redistribute itself evenly when in contact with an area that is not abundant with this gas, in spite of forces that may try to keep it back, including gravity, provided that the thermal motion is greater than whatever the forces keeping it back.

Simply put, chaos rules.

I'm starting to buy the sediment theory right now. Just poured a couple pints and everything seems to be back to normal. Color is still a bit darker, but the esters are back and the sharpness is gone. I still think the alcohol content is higher but at least its drinkable again.

Ok - found the problem.

I was right, my beer was getting stronger, darker, and the flavor was changing. I now know why. My fridge was set too high and I was freezing the water out of the beer. I now have a keg shaped ice block melting on my patio. I don't have a controller on my home made kegerator, I just assumed putting it on the lowest setting was good enough. Lesson number #3 learned from this batch.

Kinda off topic but someone mentioned oxidizing a few bottles for a taste test. Whats the best way to do this? Just shaking the piss outa the bottles right before you cap them?