Splitting 5gal batch in secondary head space concern?

I have a question regarding splitting a batch that I'm hoping someone could answer. Here's the deal...

I'm making an extract wheat beer for the summer, and was planning on racking it to two secondary carboys onto fruit - 2.5gal onto raspberries in carboy 1, and 2.5gal onto blueberries in carboy 2. I have the wheat in the primary ale-pail, and for the carboys, I have a 5gal better bottle and a 6.5gal glass. My goal was to split the batch at secondary and put them in their respective carboys with the fruit for another week.

Will the beer be OK if I split it like this with that much head space in each carboy, or should I just stick with just one of the fruits (raspberry) in one carboy?

I've looked at a few other threads regarding secondary head space, but none of them have gone terribly in-detail. Allow me to diffuse a few questions before they roll in...
- I don't have a kegging system or access to CO2, so I can't purge the carboys as some have recommended in other threads.
- I don't have any smaller carboys, such as 3gal ones.

Feedback or suggestions? I don't want to risk oxidizing the beer if it would be safer to avoid that much headspace. Thanks in advance!

There is always a risk of oxidizing your beer, even if you go to a full carboy. If it were me personally, I would not risk it, but that is your call to make. Personally, I would stick with the one fruit. But once again, that is your decision to make. I can't say for sure that it will oxidize, nor can anyone else. Is there a chance, yes, guaranteed to oxidize? no. Just my thoughts. Good luck.

I do lots of fruit add to wheats for the SWMBO. I have never had an issue with oxidation. Usually a secondary fermentation will kick up and eat the sugars in the fruits causing some more co2 to be off gassed. Since it is heavier than air it should protect your brew as long as its not moving around. I have never had that much head room but I have had 3.5 in a 6.5 carboy with no issues. My recent porter went to 6.5 secondary with 4gals for a few weeks for adds and no issues there either.

The way I look at it is as long as I am careful during racking and careful not to move or shake the carboy then the co2 that is off gassed will protect my brew.
YMMV

+1

Given that you're racking onto fruit, you're likely to get enough CO2 production to fill that headspace and reduce the oxidation risk.

For what it's worth, I've split a batch and used a 6.5 gallon Ale Pail as a secondary for three ounces of beer, and it was one of the better beers I've made. No problems and no off flavors. And that was just a secondary onto vanilla beans and cacao nibs, so like others said, you'll have some more fermentation with the fruit which will produce more co2.

Thanks for the responses! I'm kind of on the fence about it, leaning towards splitting it still. The fact that fermentation will kick back up again producing more CO2 will probably make it OK - I'm willing to risk it if it turns out awesome.

I'll join the camp that says to do it. As stated, since you're racking to add fruit you're going to have more fermentation and CO2 to protect your beer from oxidation. Plus, wheat beers are typically good young so you can drink them nice and early before any effects of oxidation would be perceived anyway.