Keg priming with fruit

[mongo]

Hi,

I have a 15.5 gallon Huff-Stevens filled with a Belgian ale that's fermented but not carbonated. I'd like to add about 15 pounds of raspberries to it and seal the keg; there is probably enough yeast in suspension to re-start fermentation. So, my question is, how do I avoid over carbonating? Thanks for your suggestions!

Cheers,

Mongo
Manchester Brewing
Concord NH

[Moonlight]

Figure how much sugar is in the fruit. Figure how much carbonation will result. (Assuming no non-saccharomyces) If there is too much priming sugar, vent the keg until gravity drops sufficiently, then bung.

[mongo]

carbonation

I've used non-traditional primers in the past. You can assume that the fruit contains WAY too much sugar for adequate carbonation. The problem is how to deal with that. Also the keg is already bunged while fermentation is taking place.

Figure how much sugar is in the fruit. Figure how much carbonation will result. (Assuming no non-saccharomyces) If there is too much priming sugar, vent the keg until gravity drops sufficiently, then bung.

[Moonlight]

Put the keg in a very cold room with a cleanable floor. Get a carbonation chart of Temp/pressure/carbonation volumes. Hook up a keg coupler that has the beer line plugged and a pressure gauge with valve on the gas side-without a check valve. Vent the keg repeatedly down to the corresponding pressure for that temp and the desired carbonation. Later you can move it to a less cold room where the carbonation will vent more readily.
Plan ahead next time!

[mongo]

Carbonate it

For me, this IS planning ahead...before I add the Raspberries!
Thanks for the idea, I'll do the gauge and coupler thing.

Plan ahead next time!

[Moonlight]

Sorry, I misunderstood! Far easier before than after! Use the chart for whichever temperature you want to use. Just try to keep the pressure from getting too high, as it is more difficult to remove it after. Consider a bit of headspace so the blow off is gas and not raspberry foam.
Search for "bunging" for other forum ideas normally used on tanks. There are adjustable pressure blowoff valves that would do all this automatically, but they may be overkill for what you are trying to do. Some simpler/cheaper ones could work, but fermentation blowoff goo could challenge them.
Maybe reserve a sealed no-air portion of beer, and only ferment say 4/5 of the keg full, then add back? I guess so much depends on how vigorous your fermentation is. With just a little yeast it could go slow enough for foam not to be an issue. Good luck!
P.S. How will you get the beer out without the raspberries plugging the tiny Hoff-Stevens valve?

[mongo]

Carbonations

P.S. How will you get the beer out without the raspberries plugging the tiny Hoff-Stevens valve?

Hmmm. Hadn't thought of that. Maybe I could put the berries in a mesh bag? Then sort of feed it in like a sausage...

[mongo]

The Results of Fruit Priming

Thank you everyone who replied, online and off.
Duncan from Grizzly Peak hit the nail in the head when he told me how tricky priming with fruit was! I spent a day looking for a coupler in the keg thread, didn't find one and decided I could build a gauge from some parts I had laying around. The keg blew in the brewery the night before I got it together, making this huge raspberry bomb that coated my cold room with fruit. Most of what was ejected from the bung hole was raspberries, fortunately, so I saved the majority of the Belgian. It smelled great and looked really red, tasted very tart though nothing like New Glarus' famous brew. I ended up force carbonating the keg. It turned out that the raspberry mush came right out of the line when I served it, which I anticipated with a sieve and pouring pitcher. I would guess that nearly all the sugars were converted to alcohol, as the brew was very dry and not sweet at all.