Grape Juice Plus is a euphemism given to champagne by Dr. Lewis Dixon concerning the beverage as an explanation to Dr. Zira. In 1973, the ape-o-naut, Zira was offered a glass of champagne by Dixon, at the party in the hotel suite. When Zira inquired about the beverage, Dixon told her to "...think of it as grape juice, plus." Zira immediately developed a fondness for the drink, and decided that grapes were her new favorite fruit.
A short time later, Presidential Science Advisor, Dr. Otto Hasslein encouraged Zira to consume the "grape juice plus" in order to intoxicate her. Hasslein subsequently questioned the inebriated Zira as to the nature of Ape culture and the potential futuristic downfall of mankind.
Only a small volume of the alcoholic beverage was required to alter Zira's judgment. After a few sips of the drink, she became heavily inebriated and quickly fell asleep.