Help, I Got Sour Cider

So I made a pretty standard batch of cider, 4 gallons of kick-butt cider (pasteurized but with no preservatives) bought fresh from a cider mill, one half gallon of the same kick-butt cider mixed with rasberry (also pasteurized with no preservatives), disinfected the carboy and airlock, dumped the cider in straight from the jug (i didn't pasteurize cause i figured it had already been by the mill), then added champagne yeast (what my recipe said to use) and put it in my dark closet to ferment at around 65 to 70 degrees.
anyway i transfered the cider into a second fermenter after the initial fermentation had subsided and I siphoned a small glass of the cider out so i could taste the progress and it smelled kind of sour and tasted even more so.

so here is my questions, did the batch go bad? does it sound like it got contaminated? Should i have pasteurized and added sugars to the cider to make it sweeter? Is there something i can do at this point to sweeten the cider and save the batch?

thanks
-jon

You used champagne yeast - that will ferment off all the sugar so that only the acids are left. That is probably the sour taste. Next time use an ale yeast like S04. Over time the acids will mellow, but it could be as long as a year. You can backsweeten. Were you planning to bottle or keg this?

I was going to bottle it.

You could use Splenda to backsweeten it. Be sure to use priming sugar also.

If it is just sour that would be pretty normal, though it shouldn't smell sour. If it has a vinegar or nail polish remover smell that is a concern. Sourness can pass away with a malolactic, which often happens by itself. In time the natural apple flavour gives a sort of sweetness without having to add sugar, though IMO if you want to make cider you should get used to having it dry, I don't like any residual sweetness in my cider but these days people get used to everything being sweet.