[homoeccentricus]

Is there really a danger for oxidation if there is too much (which is what?) headspace in the fermenter? In Belgium people freak out from the tiniest amount of headspace, especially during lagering. If that were the case, bottling from primary (which always requires more headspace) would result in lower quality beer, right?

And, side-question: what's the deal with lambics and headspace?

[JT]

Headspace during primary fermentation is great for obvious reasons, it will be filled with co2 without risk of oxidation.  After primary though there is a risk of oxidation from extended aging in a vessel that isn't airtight.  Co2 is heavier than air, so it sinks and stays on top of your beer for a while. 
If there is a bright side to carboys (especially 5 gallon carboys), it is that they can be filled to the neck which is very narrow and reduces surface area.  I haven't found this necessary for normal brews, but for a brew with bugs or an extended aged beer it would likely be beneficial to transfer to a small carboy and fill to the neck. 

[homoeccentricus]

The logic is irrefutable: if, in general, there's no need to rack to secondary, then the headspace story is mostly kitchen swill for pigs, also known as hogwash.

Correct?
 

[majorvices]

Yeah, I wouldn't worry about the head space in the fermentor. There have been a few times I have left foil on the primary fermentor past what I feel was the "safe zone" and felt like ait had gotten in the head space and I have purged with a tank of co2 before putting on an airlock, but aside from that I never have a concern.

[HoosierBrew]

I ferment 5.5 gallon batches in 8 gallon buckets.  No oxidation issues.

[klickitat jim]

I think the headspace concern with a bug fermentation is that too much O2 exposure can lead to acetic acid (vinegar). Or so I have heard.

[homoeccentricus]

I think the headspace concern with a bug fermentation is that too much O2 exposure can lead to acetic acid (vinegar). Or so I have heard.

Yes, you should taste my raspberry lambic vinegar. It's awesome! 

[homoeccentricus]

I think the headspace concern with a bug fermentation is that too much O2 exposure can lead to acetic acid (vinegar). Or so I have heard.

Yes, you should taste my raspberry lambic vinegar. It's awesome! 

But then there is still a factor luck: I added fruit to two batches of lambic. The raspberry became vinegar, the redcurrant, with a lot more headspace, was ok.

[erockrph]

I think the headspace concern with a bug fermentation is that too much O2 exposure can lead to acetic acid (vinegar). Or so I have heard.

Yes, you should taste my raspberry lambic vinegar. It's awesome! 

But then there is still a factor luck: I added fruit to two batches of lambic. The raspberry became vinegar, the redcurrant, with a lot more headspace, was ok.

It's not headspace that is the issue directly, but oxygen exposure. If you have a lot of headspace but a tight seal on one fermenter, and little headspace but a leaky bung on the other, then the headspace becomes a non-issue in comparison.

In addition, the biggest factor is presence of acetobacter. If your raspberries had more acetobacter than the currants, then you're much more likely to get vinegar from it. While Brett does produce acetic acid when exposed to oxygen, the amount is minimal and is produced slowly. Plus, a portion of that gets turned into ethyl acetate by the Brett as well.

[homoeccentricus]

In addition, the biggest factor is presence of acetobacter. If your raspberries had more acetobacter than the currants, then you're much more likely to get vinegar from it. While Brett does produce acetic acid when exposed to oxygen, the amount is minimal and is produced slowly. Plus, a portion of that gets turned into ethyl acetate by the Brett as well.

Does acetobacter survive freezing? Because funny enough the raspberries were frozen, and the redcurrants were fresh.

[morticaixavier]

In addition, the biggest factor is presence of acetobacter. If your raspberries had more acetobacter than the currants, then you're much more likely to get vinegar from it. While Brett does produce acetic acid when exposed to oxygen, the amount is minimal and is produced slowly. Plus, a portion of that gets turned into ethyl acetate by the Brett as well.

Does acetobacter survive freezing? Because funny enough the raspberries were frozen, and the redcurrants were fresh.

yes it does. also, raspberries have lots and lots of nooks and crannies (although less so after freezing and thawing) that harbor both bugs and o2 while currants don't.

For what it's worth, I try to minimize head space when ageing for months. otherwise I just don't worry about it.

[klickitat jim]

It also helps if you don't poke your pelicle