Question about topping off with wine and then malo-lactic fermenting?

[Silver_Is_Money]

I have about 5.5 gallons of fully yeast fermented Malbec sitting in my primary carboy, and its time for it to be racked to a secondary carboy. My secondary carboy is 6 gallons, and I may at best yield only about 5.25 gallons, leaving 3/4 gallon (to perhaps a full gallon) of head space.

I want to do a malo-lactic fermentation step next, so if I top off with store bought Malbec should I be concerned that any sulfate or sulfite type stabilizer present in the commercial wine may ruin my malo-lactic fermentation and/or give me an off taste.

I have an under the sink RO unit, and I was also considering topping off with RO, but for this I'm concerned about it being oxygenated. If I go this route, will boiling (followed by cooling) drive off any to all of the dissolved oxygen?

Looking for some quick advice.

 

[jgmillr1]

Your best bet is to simply get a 5-gal carboy. If you are going to use the 6-gal carboy, then you are correct that the headspace is a concern. You have several options to deal with the headspace.
(1) Purge the carboy and headspace with nitrogen or CO2, if you have a tank. If you don't have a tank, you should consider getting one since this is something you will be doing every time you rack your wine anyway.
(2) Top off with a similar commercial wine. Doesn't have to be great, so just a 5L Franzia is good enough. It is extremely important to be sure that the wine you use does not have sorbate since the malolactic will turn that into the dreaded geranium taint. This is simply avoided by not using a sweet wine. Sorbate likely would not be listed on the label as it is not required. The sulfites should be diluted sufficiently to not interfere with the malolactic bacteria, but this is an assumption unless you can measure the incoming sulfite level.
(3) Top off with water. I would lean to using a gallon jug of distilled water from the store rather than what comes out of your tap. Chief concern is the presence of chlorine that may give you TCA (dreaded cork taint) with some concern with dissolved oxygen level.

Again though, best option is to get a 5-gal carboy. You'll likely find it useful in future wines and it isn't too much more than buying 3/4gal of wine from the store to top off with.