First blow off, what happened?

Brewed a 1.080ish beer last night. Maris otter, with a little C75, and black patent. Mashed at 150-149. Made a 2L starter, and pitched at 6PM. Aerated with pure O2 for 45 seconds about 5 minutes later. 5 gallon batch into a 6.5 gallon carboy that is sitting in a bucket of water at about 67-68 degrees. Went to check on the beer this morning at 9 and the top had blown off. Any thoughts as to what could have done this? Should I just use a blow off tube for big beers in general? This isn't the first big beer I've made, but the first blow off I have had.

Lol yep I always go with a blow off tube for the bigger beers. Your yeast was happy!!! Must have been a perfect set up for them, good job

Healthy fermentation causing high levels of CO2. Blow off tube is recommended, or maybe some Fermcap-S.

Well, you did about everything in your power to ensure a powerful fermentation. Low mash temp, big beer, big starter, lots of O2, fairly high temperature - past that, it all depends on the yeast strain really. If you're using a good top-cropping yeast strain, I would certainly use a blow-off for such a beer.

I just use some press n' seal wrap as an air lock...If it blows off then I just use new wrap...It's better for me than worrying about changing air locks and tubing for blow off. It sounds like you have a fine fermentation going.

Blow off is a good thing. You can even just let it continue to blow off naturally...Open fermentation is just fine. Air locks are not insurance of anything.

You effed up, you trusted it

I do all fermentations in 6.5g glass, and regardless of the batch characteristics I always start primary with 1" ID vinyl into a gallon vessel half filled with a Star San solution. Period. End O Story...

Cheers!

I ferment everything in 6 gal better bottles.
I use fermcap in every batch.
Never have a blow off, I'd hate to lose the beer!