Secondary in Sealed Kegs - Malolactic Fermentation

[Iseneye]

I've been brewing cider for a few years now and have generally gone primary in carboy - secondary in carboy - bottle. We do our own seasonal pressing so it is about a year from pressing to drinking.

Last season (Southern Hemisphere) I did primary in carboy - secondary in carboy - transferred to keg. The keg was left at room temperature for two or three months and is now on tap and drinking nicely.

This year I will be fermenting and secondarying (sp) in kegs. Previously secondaries are in carboys with airlocks so any CO2 that builds up escapes. My understanding may be incorrect but during the secondary phase it is clearing and due to the long secondary time malolactic fermentation is occurring. To avoid getting oxygen in the secondary keg I would like to blast pressurize to 20-30PSI and then keep it locked and topped up with CO2 occasionally at about 10PSI. Is this going to cause issues with malolactic fermentation?

For reference the yeast is WLP775.

Thanks.

 

[Mr_fleabite]

MLF produces CO2; however if you have it under pressure, it's that much harder for it to escape. CO2 retained in solution results in carbonic acid. I'm not entirely sure but my hunch is that it would make MLF harder/slower (I've never done MLF under pressure).
I don't think the pressurization is necessary, keeping it topped, with as little exposure to air as possible is sufficient...if you have a bit of head space you could keep it gassed weekly with CO2. I would avoid sealing it off completely, let the CO2 from MLF escape and keep it topped, a few square cm of exposed liquid in the neck of the vessel is nothing to worry about with an air lock on top.

 

[Iseneye]

Thanks for the reply. Due to fermenting in a keg and transferring to the same sized keg there will be substantial headspace. There will be maybe 15 -16 litres in a 18-19 litre corny keg once transferred.

I am now thinking I'll just keep it under low pressure - say 5PSI and release fermentation pressure build up once a week or month.

 

[Mr_fleabite]

If you don't have anything you can top it with and it sounds like you'll have substantial head space I'd spring for some argon gas (if it's in your budget, some wine shops sell small 16oz cans of it). Argon will work much better and stick around a lot longer than CO2. The tried and true option is to find something to top it with even if you have to make a quick 1 gallon/ 3.78 liter batch or use concentrate/juice.