Because apple juice has a low pH of approximately 3.4, it is an acid. On the pH scale, a substance that has a pH lower than 7.0 is considered acidic. Some examples of other acidic substances are vinegar and lemon juice.
Many citrus fruit juices, such as pineapple, orange and grapefruit juices, are also acidic based on pH. For example, canned pineapple juice has a pH that ranges between 3.3 and 3.6.
The pH scale ranges from 0 to 14, where 7 is considered neutral, below 7 are acids and above 7 are base substances. The most acidic substances have the lowest pH values, while a pH that is close to 14.0 indicates very alkaline substances. Two examples of very alkaline compounds are ammonia and lye.