The food synthesizer (or food processor) was a common receptacle used aboard 23rd century starships and starbases for synthesizing foods and beverages. These food receptacles served as a supplement to the ship's chef and were predecessors to 24th century replicators. Unlike replicators, where food orders were made by voice command -- food orders given to food synthesizers were made by program tapes or cards inserted into a slot.
In 2268, while the USS Enterprise was infested with tribbles, it was discovered that they had gotten into the food processors aboard the ship through one of the ship's air vents. (TOS: "The Trouble with Tribbles"; DS9: "Trials and Tribble-ations")
Nurse Chapel offered the surviving children of the Starnes Exploration Party a selection of cards with differing flavors of ice cream to choose from. All they had to do was pick a card and the computer would mix their favorite combination. (TOS: "And the Children Shall Lead")
Upon taking on a contingent of Klingon officers, lead by Kang, aboard the Enterprise, Captain Kirk ordered Johnson to have the food synthesizers programmed to accommodate their guests. (TOS: "Day of the Dove")