Have you tried/made cider before? It generally is rather tart and once it ages at least 6 months it mellows out. After a year it is even better. If it was infected it would form a thin white layer on top, mold or have a change in cloudiness.
Brew blog: Daniel's Home Brew
Primary: Lemongrass Witbier, Sweet Cherry Cider, Belgian Cider (D-90 Candi Syrup & Witbier Yeast)
Secondary: Barleywine (Marris Otter, CaraRed & Vienna and 100% Fuggels Hops)
Bottled: Hibiscus Witbier, Coffee Porter, Pinot Noir