If primary fermentation stalls, is there a risk of oxidation?

[CaptainProg]

I'm trying to get my head around the concept that oxygen is good for fermentation, yet bad for finished wine. My current (possibly incorrect) understanding is that the reason we can 'get away with' exposing wine to oxygen early on is that the active process of fermentation produces a jacket of CO2 which protects the wine from the oxygen.

If that is correct, then does this mean that a primary fermentation (i.e. exposed to air) that stalls will be spoilt, since it is exposed to oxygen without the protective CO2? Or, does all the 'badness' undone when a stalled fermentation is restarted (so long as it has not stalled when the wine is already dry)?

 

[Coffee49]

Key to the starting process is to avoid contamination, having the proper seal (bung and airlock) prior to startup is paramount, as fermentation begins a larger amount of airspace is required to permit release of gasses from primary, as fermentation slows so does the release of gasses which ultimately blanket the juice from O2 contamination. Bung and airlock is the only protective cap when the positive pressure released equalizes to outside pressure. That also protects contents if a stalled fermentation occurs. Getting back to stalled primary, maintaining 24C temp is first objective, I would give the mixture a light stir to wake up the suspension, if that fails, pitch some nutrient and another 4 grams of yeast and wait

 

[Kickass]

Yes, O2 is replaced and subsequently diluted with CO2 as CO2 produced during fermentation pushes the atmospheric gas out of the air lock.

Two additional facts:
1. A “blanket” is not created. Gasses mix. The blanket explanation is an often referenced myth.
2. Yeast need O2 to function. Yeast will absorb dissolved O2 that exists in the must so they can go to work.

To answer your question, it depends when it stalls and why. If you started with healthy yeast to took care of the O2 dissolved in the must and there was enough fermentation to dilute and replace head space O2, then you’re probably ok.

Can you reference you OG, FG and stalled timeline? That might help the “wine people” answer your question more completely. I’m a beer guy with a little mead experience.