Oxidation - a real concern?

Can someone please explain beer oxidation and it's actual implications? I understand generally what oxidation is, but I do not understand:

1) what in beer is oxidizing (the unfermentables?)
2) aside from an impact of color, how does it impact flavor and is this impact actually noticeable to the average drinker?

I constantly hear about avoiding oxidation but I've never really understood it, and haven't found a good explanation. I'd like to know why I'm avoiding it so desperately.

There's a lot of misinformation about oxidation going around this and other websites. It had become the boogey man to explain problems when other explainations were not ovbvious. Hot side aeration/oxidation is a myth.

On the bottling side, I've had quite a bit of bubbles when transfering to a bottling bucket with no ill effects. That being said, I wouldn't purposely try to introduce extra oxygen into my bottling bucket - appropriate handling will reduce the oportunity for problems of all sorts.

Oxidation is typically associated with papery, sherry-like, or cardboardy flavors. The chief compound responsible for these flavors is trans-2-nonenal, which is formed by the oxidations of lipids in the malt. The effect of exposing beer to oxygen is usually not immediately apparent, but over time the dissolved oxygen will create very obvious oxidized flavors. Commercial breweries spend a great deal of money minimizing the dissolved oxygen content in their beers, because their beer needs to have a long shelf life. If you go through your beers quickly, you don't need to quite so concerned, but you should still take reasonable steps to avoid oxidation.

If you want to know what oxidation tastes like, take a pale ale and leave it in the attic all summer.

Gavagai gave the key points. Oxidation is a staling of beer. The more you introduce oxygen, the quicker your beer can stale. The reason why commercial brewers spend so much on this is it extends their shelf life, allows beer to taste fresh longer, etc.

If you want to accelerate this, as Gavagai said, put it in the attic or some other hot place.

Some beers are affected differently compared to others. Typically darker beers will get the sherry-like, stone fruit type tastes. Lighter beers will get the more papery/carboard. I've never noticed the papery/cardboard, but have tasted bland stale beer (compared to what the beer once tasted like).

The two places that brewers really get concerned about oxidation is with respect to hot wort and finished beer. There are a couple of simple experiments you can do with each of these to see what the effects are. Brew a batch of one of your favorite beers being as careful as you can to avoid exposing the mash and wort to oxygen. Don't splash, pour vigorously stir.... Now brew another batch but go out of your way to introduce oxygen. Stir the wort to a froth a couple of times before adding running through the chiller.

The other experiment would involve getting two sixpacks of some beer you like. Chill the beer to close to freezing then take the caps off one sixpack, pour off perhaps 1/3 the beer (what you do with that is up to you) and then force compressed air or, better yet, if you have an oxygen bottle, O2 into the head space with enough vigor to displace the CO2, recap and put away. At the end of a month open one of the treated bottles and one of the untreated and compare taste. Do this each month until you have used up all the bottles.

A lot of beer gets oxidized in bottling, most often with a beer gun. I don’t keg, but I am told it can be done right. However in judging, most of the oxidized samples were kegged, based on the lack of schmutz at the bottom of the bottle.

When I bottle I take the bit that glugs out when the siphon starts and the last part when the siphon empties and set it aside. Recently I combined the bits and capped it. I marked the cap with a big ‘O’. I tried it after a few weeks and it was fairly undrinkable.

On a related note, Aren’t oxygen barrier caps a scam? It seems like there is going to be way more oxygen in the head space than those little caps could eat.

keep in mind that there are beers that benefit from oxidation. These are mostly dark strong beers like Doppelbock or RIS.

Kai

Wynne-R said:

On a related note, Aren’t oxygen barrier caps a scam? It seems like there is going to be way more oxygen in the head space than those little caps could eat.

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Shouldn't be if you 'cap on foam'.

ajdelange said:

Shouldn't be if you 'cap on foam'.

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I always figured what little oxygen is left may get eaten by my yeast when I bottle condition. I have some two year old bottles that don't seem to show oxidation.

One noted beer scientist, Charlie Bamforth, has said in an interview that homebrewers should not concern themselves with HSA. However, he did caution about introducing O2 into the beer during bottling, or at any time post-fermentation. It's so much easier to prevent oxidation when kegging. Purge air with CO2, fill keg, seal and purge air again, then pressurize. There is hardly any chance for O2 to enter the beer if done right.

Think about this for a minute. You have 1 atm absolute in the keg. You pressurize to 2 atm gauge which is 3 atm absolute with CO2. You have, then .2 atm O2, 0.8 atm N2 and 2 atm CO2. You bleed down to 1 atm which gives you 0.2/3 atm O2, 0.8/3 N2 and 2.0/3 CO2. Pressurize to 2 atm gauge again and bleed down again and you have 0.2/3/3 atm O2, 0.8/3/3 and the rest CO2. Do it again and its 0.2/3/3/3 = 0.007 atm i.e. 0.7% O2 still in the keg. To beat this some fill the keg with water and push that out with CO2. I fill the keg with steam in order to sterilize it and circulate that steam for 15 min (these are Sankeys). At the completion of sterilization the keg is disconnected under pressure from the steam source and connected to a CO2 bottle. As the steam condenses it is replaced by CO2. Excess CO2 then pushes the condensate out.