first timer at both cider and kegs.
I have been reading that pumping oxygen (air) into a keg as the beer level goes down in order to maintain carbonation is bad as the oxygen will reignite the yeasts and alter the beer's taste. Is this still true for cider ? Do I really need CO2 tanks for the job ?
Yes you will oxidize the cider (or beer or wine) if you don't use CO2 or some other inert gas like Nitrogen (but that has it's own problems). Oxygen will not "reignite" the yeast. Yeast will happily ferment with CO2 or Helium or Nitrogen or whatever gas you use. Make sure your cider is done fermenting, then put it in the keg. Purge the headspace with CO2. Then seal the keg and charge it up. You will need to put it in a fridge to get to serving temperature. At this point, just treat like beer and there are many articles about how to keg your beer.
Adding oxygen doesn't maintain carbonation, and this is even if the oxygen addition is pressurised. Only CO2 will help to maintain actual carbonation, as it's carbon dioxide which is released during fermentation. Adding additional CO2 as the keg empties both creates the pressure required to get the brew out of the keg, and ensures the brew doesn't go flat, and doesn't change the flavour of the brew in the way that other non-inert gases might.
That said, there are a number of small keg devices where you can use a built in hand pump to push the brew out of the keg. You are less likely however to notice oxidised flavours at first, and more likely to find the brew starts to taste flat. This is because oxygen is released more quickly from the beer than the CO2, and in doing so is likely to "pull" some of the CO2 out with it.
All that said, some ales can benefit from a small amount of oxidation, particularly when they've been formulated to be drunk without additional carbonation, however these are brews that generally don't keep well (agitation increases oxidation), and so they need to be drunk relatively soon after kegging. These should generally be dipped or pumped out, rather than pressurised, to reduce introducing additional O2 to the brew.
You don't necessarily need to purchases a huge CO2 rig to maintain carbonation and pressure, although this is the optimal configuration in most cases. There is also the option - preferably for small kegs of 5L or less - of using an adapter for readily available Soda Stream gas bottles (or similar). If you're using larger kegs, you'll need a larger rig.
Yes oxidation is an issue for most if not all, fermented drinks. If you don't want to invest in a full tank, you can buy cartridge adapters for your system, which will maintain CO2 pressure for serving.
