I bought a bottle of cranberry juice which said "100% juice" on the label. But, later, I found that the label said it included apple juice. I became confused and suspicious about fruit juice labels, a state which lasted many years.

But it turns out that fruit juice labels are pretty comprehensible. I learned this from user rumtscho's lovely post on this topic at cooking.stackexchange.com. The following is just a restatement of that post.

A manufacturer who sells juice can label it in one of three ways:

• 100% juice, not from concentrate.

  • This means that nothing has been added or taken away from the juice. It is what you get when you take some fruit and squeeze it. (Possibly it's been pasteurized afterwards.)

• 100% juice from concentrate.

  • This means that, in order to ship the juice to the store more cheaply, the manufacturer has boiled some of the water off. The same amount of water is then put back in before it is sold at the store.

• X% fruit juice drink/cocktail.

  • Note this can't legally be called "fruit juice" anymore; instead we use these other words. This means that the manufacturer has added $100\% - X\%$ of water to the original fruit juice. The water may contain other things like sugar or citric acid.

Nowhere is it stipulated that the fruit juice must be all from the fruit on the label. So your X% cranberry juice may be slightly or mostly apple juice. This is common because some juices are much cheaper than others.

Bonus: A 1991 NYT article on juice labeling, featuring quotes from the juice industry pushing back!