Corny ferment - volume & adjustments

I'm hoping to ferment in my fridge using 2 ball lock kegs with a blowoff on the gas in post. I've read the corny as primary threads, and am just concerned about blowoff, as 5 gallons comes up to the weld line, only leaving a few inches of headroom in my ball lock corny.

Basically, instead of doing a 3gal boil and topping to 5gal like I would in my carboy, I'm planning on a 3gal boil, topping to 4.5gal for the corny and adding the final half gallon when I transfer to a serving keg.

Would the lower volume during ferment effect anything?

Thanks!

This is a technique that others have had a lot of good success with, so you shouldn't have too much trouble.

I suspect that if you dry-hop, you'll get less extraction using the higher-gravity wort. The yeast also will have trouble if your gravity is really high. That said, the extra half-gallon of liquid shouldn't make too much of a difference for either variable.

One thing I would be concerned about, however, is the process of mixing the fermented beer with the water. Definitely purge the serving keg with lots of CO2 before you transfer, and then shake the bejeezus out of it to mix thoroughly.

pericles said:

I suspect that if you dry-hop, you'll get less extraction using the higher-gravity wort. The yeast also will have trouble if your gravity is really high. That said, the extra half-gallon of liquid shouldn't make too much of a difference for either variable.

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Shouldn't be going much over 1.060 at the moment, and I will dry hop in the serving vessel, after I've added the water. I just wanted to make sure that I was thinking correctly in not having to adjust my recipe, and only having to adjust my final volume of liquid. I may end up doing 5 gallon ferments, but as with many things, I need to see it for myself before I believe it, and I'm not readily willing to sacrifice time or beer where preparation can be a replacement!

Thanks for the feedback!