Primary Fermentation to serving in one Keg?

Something here has caught my eye and got my brain cranking along. I apologize for not crediting the original poster (I can't remember who it is or the post involved) Update: Sanspareil in topic Primary Fermenting in a Corny Keg

I have been considering setting up a sanke keg as a fermenter, but someone here mentioned setting up a burton union off of a corney (ie. this picture, but with gas and liquid disconnects)

I was hoping having the additional sealed gallon container connected would act as additional headspace so that I could ferment the whole 5 gallons without using foam suppressant, plus collect the yeast so that it wouldn't pool on the bottom of the keg.

Then I thought when the primary slows down place a spunding valve on the gas outposthttp://***********/images/stories/116-1614_img.jpg to naturally carb the beer (as per the Closed-system pressurized fermentation technique! thread. I could have my beer go from brew pot start to finish in one sealed unit.

I wouldn't have to modify my kegs, and I could use all of them as primary fermenters /serving units just by swapping off the burton union and spunding valve.

I was then thinking I could use it for no chill brewing (hot liquid wort into sealed keg) reserving some wort for yeast starter, which would get poured into the sanitized burton union and then connected to the corny to get the fermentation started.

Benefits:
* Stainless Fermenter (No broken glass or scratched plastic)
* Completely sealed fermentation
* Fermentation to serving from one vessel
* All cornies would be interchangeable (no modification)
* would be able to ferment the full 5 gallons in a corny keg without using foam suppressant.
* yeast would be easier to collect for reuse

Am I talking out of my butt, or would this be possible?
I'm planning on starting construction of the burton union and spunding valve this week. But if someone else has attempted this (and found that it doesn't work) I'll save myself the time and money of constructing it. I have heard that the shape of cornies aren't optimal for fermenting, but I cannot see how the slight depth difference in a keg would increase pressure on the yeast as opposed to a 6.5 gallon bucket.
Keeping my fingers crossed.

personally i doubt the preassure on the yeast will be much different from my experiences...My preference has always been and most likely will always be glass carboys (6.5 gal) for primary fermentation until the day i get a conical. The stainless steel is an attractive option in your case however the cleaning of the system (gas and liq posts, pop-its etc) seems like its more trouble than its worth. Seems like alot of trouble to go through to ferment 5 gals in a corny. Theoretically i also believe you will decrease the yeasts contact with the fermenting beer since it will most likely be top fermenting strain and the 5 gallon mark on a corny leaves almost no head spacer...much of the yeast and krausen will sit in the top container when it should be in contact with the beer.... just my $.02

I've fermented in cornys for more than 10 batches now and find it much easier to siphon from and clean than my carboys, but I do have a water pump to push cleaner and sanitizer through both posts of my kegs to make it almost automated. Regardless I think a beer could be fermented from primary and served in the same keg. Haven't done it yet myself though I will try. I use fermcap and have only had one blowoff, so I haven't found it necessary to research the burton union. This is with at least five gallon batches. I no chill and use real wort on stirplate for starter.

The criticism for this would be when does the beer clear? When I transfer to secondary I push the beer with c02 of course and there is sediment that I discard until the beer is running clear than attach my jumper to my keg. Why couldn't someone primary in keg with spunding valve to carbonate, cold crash when fermentation is done for however long you see fit for aging, and then discard first pint or two of sediment drawn bottom of keg till beer moves clear. The key would be to never disturb sediment which could be tricky.

I was able to partially try this experiment, with mixed results.
I did build a burton union for my corny, but I think the hose was too long in between. I was able to ferment without a mess (without using the fermcaps) but the union was either to far (20") or high(6") to collect any yeast from the fermenting process, as a result there seems to be a lot of trub in the serving keg.
I assumed that cold conditioning in the keezer would solidify the trub, so that it would not get dragged up the serving line. This has not been the case, I am still getting yeast sucked up the beer line and into my glass.

I was not able to build the spunding valve, because I could not find an adjustable pressure relief valve, so I can not comment on that aspect of my build.

I plan to give it one more try with shorter lines to the burton union, I will comment when that batch is complete.

Man, I can't believe I missed this thread. Did you ever try it out again, and if so... how did it turn out? I am still trying to work out a system for a Sanke fermentation done under pressure after the initial growth phase of the yeast (post-high krausen). I think this would work very well with a almost 100% full fermentor. Anyways, just wanted to comment and see if you had further information.

The cream ale I made turned out really well, other than having to dump trub from the beer before every session. I may try one more with shorter lines to the burton union, or just switch to fermenting in a sanke.

After some years what is your summary about this? Do you use it now? How did you refined it?
I also tried it:
I bended the dip tube of cornies, so the trub remains on the bottom. No chill. (less need of sanitazing)
No burton union, I use fermcap S and a bit headspace. RWS with stir plate. I begin fermentation with removing poppet from gas port, and assemble a blowoff silicon tube from the gas port to a bottle of water. After 3-4 days (bubbles slowing, close to FG) a put poppet back, and install spunding valve to get natural carbonization with closed system in some days.
And thats all. Goes into kegerator, and after some days I hook gas on, tap and drink.