The watermelon is the ultimate rating that a book can receive. Books that receive a watermelon rating have characters that practically step off of the page and a plot that keeps you guessing. Watermelon rated books also have the power to change the reader in some way after reading them, there is a part of the story that stays with them long after the book is finished.
Peaches step up the ratings a notch. Peaches are known for their juicy nature. Books that are rated as peaches are informative with a fairly strong plot and mostly believable characters. But there is still something fairly predictable about the peach.
An apple rating is a very respectable rating. This is obviously one step up from the relaxed rating of a raspberry. A book that gets an apple rating is more complex than it's previous ratings and in a sense has more to offer. Even though the apple rating is considered "middle of the road", in no way does that mean the book is mediocre. An apple rating is respectable because the book manages to contain substance and the ever so illusive "juice" I refer to.
A raspberry rating is appropriate for light reading, such as "chick lit". These books have enough zest to keep the reader interested but aren't the juiciest book you have ever read. Raspberry rated books are enjoyable and quickly finished because of their lack of complexity-but again, still enjoyable reads.