Malo-Lactic Fermentation process in Pony Kegs?

I've got a 50 gallon bourbon barrel of cider with a thin film of something not good. It tastes fine and the growth is just on the top surface. So I plan on transferring the cider into either pony kegs or carboys. The cider began with a potential alcohol of 6%. It now sits with an SG of 1.001. Very dry indeed (I have not added any sugar yet)

My question is this:

I've heard that cider goes through a malo-lactic fermentation period where it converts malic acid to lactic acid and carbon dioxide and that this process is often delayed until that cider warms up a bit come late spring.
Can the malo-lactic fermentation phase happen in a sealed pony keg, or do I need to allow a lot of gas to escape through an airlock? My instinct tells me that It will indeed undergo malo-lactic fermentation in the kegs, but I'm wondering if there would be too much pressure in the kegs and thus make it over carbonated.


Also,

does anyone have SG figures that correlate to a spectrum of dry to sweet ciders? For example, my barrel cider with a SG of 1.001 will surely need sugar added to it. I need to know how much sugar to add without making it too sweet. How much sugar per gallons should I add to make the cider still dry but drinkable?

Cheers,

Jon

A "film of something" sounds infected, so I'm not sure what kind of advice to give. I don't do MLF on my ciders as I like it better without it, but if you undergo MLF in the keg it should be ok. You may want to vent excess co2.

I'd solve the infection problem first, though.

You can't sweeten cider unless you kill the yeast or use artificial sweetener like splenda.
You need to keep air out and add so2 to stop infections. I would advise kegging with co2, so2 and a little splenda (or sweeten with juice as you drink it). MLF doesn't give very much co2, not enough to worry about, if you add so2 you can prevent MLF.