Headspace for a sour/fruit secondary?

I racked a saison/wit onto some blackberries last night. I racked from a 6gal carboy into a 5gal and filled that thing way full. Like up past the top line where it starts tapering in. Purple foam was flowing out the top. I ended up having to take a full wine thief sample to make room for the ~200ml of sour slurry I still needed to add.

Do you think Im gonna come home to a mess? I know there will be some additional fermentation from both the sour blend and the sugars in the berries. Has anyone actually gotten like a second krausen from something like this?

well, I guess Ill find out in an hour. Hoping my carpet doesnt get any more blackberry juice stained than it already is....

.....and it looks like I needed more headspace. I could see active bubble rising out of the blackberries that floated to the top. Lesson learned

Here's how much headspace I had 2 nights ago (blackberries hadnt floated to the top yet):

Here's what I came home to yesterday. just barely caught it before it got messy:

Took off the blowoff last night. So in case any people in the future are wondering and stumble across this thread, you only need a small bit of headspace for racking a fermented beer onto several lbs of fruit and souring it at the same time. I only had like ~300ml of headspace so it made a bit of a mess but quickly went down. No krausen or anything. Just bubbles

Dude, got back from thanksgiving and took a look at this thing. Its like entirely pink. Cant wait to try the first sample

update: took a New Years sample, so ~40 days into souring and its fantastic. Already very sour, I think the tartness of the blackberries helped too. I didn't think to take a pH reading though.

I took the sample down to my friendly neighborhood brewery since it is the same base recipe as a sour peach beer im working out with them. Hopefully, it will help convince them to leave the grain bill as I proposed

Never had this type of beer, but id be willing to try it. Looks good.

I'm about to brew two 5 gallon batches of oud bruin to which I'm gonna add 10 lbs of cherries to one, and 10 lbs of raspberries to the other during the secondary fermentaion in a standard 5 gallon fermentation bucket. I'm really concerned if the extra space in the 5 gallon bucket will be enough for the fruit and resulting krausen from the secondary. I was just planing to put the lid on with a airlock, but I'm worried I'm gonna come home and have a mess all over my kitchen. I was thinking of buying 60 liter buckets for this, but I'm not sure if that's overkill.