Oxidation

[iamnick]

I've read quite frequently on this forum and on homebrew pages the dangers of oxidation. While I understand why it is bad, none of the sources ever say how long it will take for beer to oxidize due to mistakes in brewing. Palmer says something like "over time" the beer will oxidize...but that doesn't really help much. I hope someone can help me out with this. It's something that would be good to know, I think.

-Nick

[Chubber]

Depends on the amount of oxygen introduced. If a little touches the beer during bottling, then that will take longer than if a lot touches it.

The worst case scenario is when a hand pump is used on a keg. Perfectly good beer turns into wet newspaper overnight when pumped with air. Now that is a lot of air, and no yeast to scavenge some of the O2.

In the bottle, during bottle carbonation, the yeast will take up some of the O2 that is present. Another reason to add a little corn sugar to your keg and let it naturally carbonate for a week or two before chilling and carbonating. The yeast activity scavenges the O2, keeping the beer fresher longer.

The bad part is that oxygenation is cumulative and non-reversible. Any wort or beer that oxygenates essentially "rots" and will cause off flavors. That is why the wort must be cold when oxygenating prior to pitching the yeast, to slow that chemical reaction. And you don't oxygenate except for the first time or three, over a couple of hours max. The super active yeast eat the O2 before it has a chance to do much damage. Once the yeast get into alcohol production, they don't do O2 scrubbing as well any more, so you have to be more careful.

But even some bottled beers don't show the oxygenation until months down the road because the amount of O2 in the beer is very low. I just had some Dutch beer that was so oxidized that it was almost undrinkable. It was almost 3 years old, too old for a Pils.

Transfer wort without splashing. If you keg, flush carboys and kegs with CO2 before racking into them. If you bottle try to have the right head space and cap on foam (foam bubbles are almost pure CO2). I use Oxy-caps. Jamil Z likes to dip the necks of capped bottles in wax if he is ageing a beer. All will help cut down on oxygenation. Some people even go so far as to keep from splashing when mashing, though hot water holds a lot less O2 than cold water.

In short, worry about it, but don't worry about it too much.

[iamnick]

Thanks, Chubber.

I have a little cofusion, though. I always wait until my wort is below 80* F to aerate it as I believe this is the rule of thumb...but I guess I don't understand why I couldn't just dump it in at a higher temp since the yeast are going to use the oxygen anyways. Will this put too much oxygen into it? Or am I missing something...

I'm guessing the latter.
-Nick

[Chubber]

Originally posted by iamnick
Thanks, Chubber.

I have a little cofusion, though. I always wait until my wort is below 80* F to aerate it as I believe this is the rule of thumb...but I guess I don't understand why I couldn't just dump it in at a higher temp since the yeast are going to use the oxygen anyways. Will this put too much oxygen into it? Or am I missing something...

I'm guessing the latter.
-Nick

Oxygenating hot wort won't put too much oxygen, it will put too little O2 in it. Gasses are more soluble in liquids at lower temps. And the oxidation (rotting) chemical reactions are slowed. So, at lower temps the wort will both hold more O2 and it will do less damage while the yeast use it for reproduction.

Yeast are either reproducing OR making alcohol. They can't do both at the same time. They need O2 to reproduce but not for making alcohol. That is why you want the O2 up front but not for long. Another good reason to make a monster starter. The more yeast reproduction in your starter, the less you have to oxygenate your main wort, risking oxidising the sugars into cardboard.

[iamnick]

Thanks again. I'll continue doing what I have been, then. I just wanted to know why.

-Nick

[BrewDog]

The hot wort will chemically combine with the oxygen much more readily than cold wort will. That's why hot side aeration is a no-no. Once the wort is cooled, the oxygen has a hard time connecting with the other wort molecules, so aeration will dissolve oxygen into the wort "between" the molecules, not attached to them, so they will remain separate.

Yeast have two ways of eating: aerobic and anaerobic. Aerobic means 'in the presence of oxygen'. If there is oxygen present, then they are happy to use that oxygen and the wort compounds directly to feed themselves. Little or no ethanol is produced in this phase. This is also when they grow the best.

Once the oxygen is gone, they need to make some in order to eat. They do this by breaking the sugars down into into what eventually turns into co2 and ethanol.

So, in the end, we are simply drinking yeast piss with yeast burps/farts dissolved in it.

[dparsons]

Originally posted by BrewDog
So, in the end, we are simply drinking yeast piss with yeast burps/farts dissolved in it.

This is how I got my son to eat yogurt.

Mmmm. B vitamins.

[Mad Scientist]

To complicate the issue further, slight oxidation from aging is sometimes desired in varities such as old ale, Impy stout, etc....

But this does not mean get crazy and splash stuff around, just let it do it on it's own over time.

[HogieWan]

Originally posted by Boerne Brew
To complicate the issue further, slight oxidation from aging is sometimes desired in varities such as old ale, Impy stout, etc....

But this does not mean get crazy and splash stuff around, just let it do it on it's own over time.

and also the reason a cask ale tastes best the second day

[Mad Scientist]

Originally posted by HogieWan
If you hit the edit button on your post, there is the option to delete it

but where is the funnin in that?