Wow, the thought of fermenting fruit juice in an entirely closed keg scares the heck out of me. I sure hope it has a good pressure-release safety valve! From making beer and cider, I ferment a batch in a 5 gallon glass carboy, with a bubbling airlock to keep it sterile. But I ferment it until all fermentation has ended, then stir in 1.5 cups of corn sugar (or 1.3 cups white sugar) and bottle it, which yields about 22-one litre bottles or 66 beer bottles. That added sugar then ferments in the bottles and carbonates the brew. The amount of sugar I add is actually about double what most recipes call for because I like a lot of carbonation. You are obviously using far more sugar than me if you are fermenting the fresh juice in a pressure vessel. Why you lose that carbonation is a bit of mystery to me because home-brewed beer and cider keep their carbonation as well as commercial brews. Sometimes brewers add "heading agents" to their beer if they have trouble maintaining carbonation. The problem is due to a lack of proteins in the brew, as proteins seem to be needed to hold onto the gas bubbles. Maybe that is your problem... lack of proteins in the fruit juice? Anyway, thought I'd mention it in case you wanted to look it up a little more or talk to someone at one of the local homebrew stores. One other thought... are you using a commercial wine yeast to ferment the juice? Or relying on natural yeasts that get onto the fruit? I'm not sure that would have any effect on the final carbonation, but a commercial yeast would give a more consistent product.

I'll kill this post so it'll drop off the board.

Hmmm - now I'm really straining my brain - because I am not sure what ratio of home-made citrus pectin is used per cup of mashed fruit - but perhaps I have it somewhere in my "saves" - which right now is at the bottom of some other "saves" because we have our grandson occuping the space I was using - well you get the idea. Anyway, when I made the pectin (you remember the postings recently - so I won't repeat it here), I froze the "gooey" stuff in cup-size portions - for a whole season, mainly because it was at a time when fruits were in season, and I couldn't get to it right away. Hopefully, I can find the ratio of pectin to use. But a good way to save pectin is freezing it. I think lemon pectin would be great, because I add either lemon or lime juice to ALL of my fruit jams and jellies anyway - brings out the flavor. Just my 2 c's. Sorry to be so confusing - Bejay

thanks for the advice! I was packing the grapes to within 2" of the top, then topping off with juice to 1/4", per the Ball Blue Book advice on juice. maybe I'll try 50% with the fruit next time. and yep, I try to leave the jars in the canner for awhile to gradually drop pressure and temp, b/c I noticed that if you open it too quickly they will start boiling over right in the jars! cheers