How big of a threat is oxidation when re fermenting beer on grapes

[BPenny]

Hey, first post here so go easy on me. I have been brewing mostly wild fermented and mixed culture beers for about 6 years. I am aware of all of the standard answers about headspace and oxidation as well as the fact that these matters aren’t always so clear when it comes to mixed culture beer. I recently racked about 4 gallons of 6% abv pale farmhouse-style beer (approx. 7 IBU, brewed 2 months ago, fermented with my own house culture) onto 12 pounds of mostly red wine grapes in a 6-6.5 gallon carboy. This left a gallon or more of headspace (see picture). This seemed like a good idea since I generally don’t leave enough room for re fermentation, which results in several days of fruit/beer bubbling out of the airlock. Unfortunately, it’s been around 2 days since I racked it and it is just now starting to re ferment so I am worried about oxidation that may have happened over the last couple days. Generally, my house culture seems pretty good at scavenging oxygen, but I don’t usually do a secondary fermentation unless I am adding fruit and I have never left this much headroom during secondary. Does anyone here have any thoughts or experience that could help me decide whether I should try to remedy the situation or just let it ride for a few months and see how it tastes at bottling?

 

[VikeMan]

A headspace that big isn't ideal, but I don't think there's really any "remedy" at this point. The headspace might be fairly low in O2 at this point (due to absorption and due to the new fermentation activity driving some out). Racking again would expose the beer to new oxygen.

 

[SanPancho]

Not stating as absolute fact, but I can say that when I’ve seen barrels being filled for aging or onto fruit that they were not purged of oxygen. But they were getting The secondary yeasts/bugs pitched along as well, and I think they were in an active state. If I recall correctly bretts will not make acetic acid during aerobic conditions if there is easier fermentation path available, such as fruit, sugars, etc, it typically happens when oxygen shows up in the secondary/aging process and simple sugars are long gone.

 

[VikeMan]

If I recall correctly bretts will not make acetic acid during aerobic conditions if there is easier fermentation path available, such as fruit, sugars, etc, it typically happens when oxygen shows up in the secondary/aging process and simple sugars are long gone.

Every real world Saccharomyces and/or Brett fermentation of beer wort makes makes some acetic acid. Fortunately, it's usually below taste thresholds.

Here's an abstract from a Brett study that showed that more O2 drives more acetic acid, even in the presence of sugar, i.e. glucose medium.
https://pubmed.ncbi.nlm.nih.gov/12655458/

 

[SanPancho]

Every real world Saccharomyces and/or Brett fermentation of beer wort makes makes some acetic acid. Fortunately, it's usually below taste thresholds.

Here's an abstract from a Brett study that showed that more O2 drives more acetic acid, even in the presence of sugar, i.e. glucose medium.
https://pubmed.ncbi.nlm.nih.gov/12655458/

golly, sorry professor.

"bretts will not make A BUNCH OF acetic acid....."

 

[VikeMan]

golly, sorry professor.

"bretts will not make A BUNCH OF acetic acid....."

It's ok.

 

[SanPancho]

It's ok.

Thank you.

And Bless your heart.

 

[mashpaddled]

It's not ideal but at this point fussing with it is more likely to add more air exposure and make the problem worse.

I once refermented a little under three gallons of sour beer on blackberries and dry hops in a six gallon carboy for a couple months without a big acetic character, so I wouldn't consider this doomed. I would rack out and package as soon as you feel like the fruit flavor is where you want. You can let it continue to age in the bottle if you want, but that will eliminate the headspace issue.

 

[BPenny]

Thanks guys, this helps a lot. I agree, that most attempts at “fixing” beer generally just make matters worse.

I’m honestly not sure what’s in my house culture since I originally harvested it a few years ago from a beer that I inoculated soley with whatever yeast/bacteria were on some wine grapes that I picked. I can safely assume there is lacto, and likely acetobacter, but it’s never produced much detectable sourness, either aceto or lacto. It’s also surprisingly clean without any stereotypical brett funk (other than some mild phenols and overripe fruit esters), but it drops crystal clear and ferments down to 1.000 everytime, so I guess it’s anybody’s guess as to what’s in there or how it will react to that much oxygen. Thanks again!