Refrigerate after opening

For the past couple of months I've been trying to stock apple juice in the house to try to convince Andy that sippy cups are a good idea. The weird thing is that after about a week, the juice got little bits floating on the top. I immediately blamed the boys for drinking out of the top, to which the first time they confessed (I know, ick) and from then on they swore not to have touched it. Turns out, juice is pasturized and needs to be refrigerated. Duh. In my defense, Bjorn didn't catch on either so it couldn't be THAT obvious. Right?