I'll just reiterate: Sulfite may be the most commonly used option. However, personally, I'm an advocate for pasteurization instead of sulfite, as I don't like chemicals in my cider. I've done it both ways but I prefer pasteurization. I heat my juice to just 160 F for 10-15 minutes, cool and pitch. No sulfites, less harm to the yeast that's pitched, less farty sulfur generated, minimal loss of aromatic compounds -- my cider is much more aromatic than many others I've tasted. Just another option. Neither way is "wrong" in my opinion, but either method will prevent contamination.