The food replicator or food machine was a device installed in TARDISes which produced bars of food. They were engineered to replicate meals in flavour and nutrition. The Doctor's TARDIS possessed one.
Features
The food machine had two large dials with selector needles on the front by which the codes for the various meals could be selected (one dial bore numbers, the other letters), and dispensed foil-wrapped blocks, served on paper plates, that looked like blocks of cheese or tofu, but when eaten tasted like whatever food had been programmed into the machine – such as bacon and eggs. (TV: The Dead Planet)
A food machine also stored water and milk, served in plastic sachets, which had to be replenished when empty because they weren't created by the machine. (TV: The Edge of Destruction)
The food machine rearranged molecular deconstructed fungus into whatever delicacy was ordered. (AUDIO: Upstairs)
Food machines came with a booklet which had codes for the food they could create. The code for eggs and bacon was J62/L6 (TV: The Dead Planet), while the code for spaghetti bolognese was KD/NB. (PROSE: Venusian Lullaby)
The machines became obsolete, though, and were replaced by kitchens. (HOMEVID: Shada, WC: Shada)
In the Doctor's TARDIS
The food machine was generally kept in the TARDIS kitchen, (PROSE: The Room With No Doors) though it was known to "wander" the corridors (PROSE: Christmas on a Rational Planet).
The Fourth Doctor once claimed that he had not seen the food machine in years. (AUDIO: The Fate of Krelos)
The Seventh Doctor's companion Ace had the food machine near her room on the TARDIS. (PROSE: Echo) At some point, she made the food machine produce actual food instead of nutrient bars. The Doctor had intended to do the same, but never got around. (PROSE: Legacy)
Uses
Vicki Pallister spent a long time programming the machine to produce a flavour like brown sauce after Ian Chesterton told her that Barbara Wright was fond of it. (AUDIO: 1963)
Steven Taylor once ate bacon and eggs from the food machine. (AUDIO: Upstairs)
The Second Doctor got a hay-flavoured nutrient bar from the food machine and fed it to a sheep that had entered the TARDIS. (PROSE: Loop the Loup)
At one point, the Second Doctor instructed Jamie McCrimmon and Victoria Waterfield on how to operate the food machine. (AUDIO: The Story of Extinction)
When Jo Grant brought a Micro Servo Robot into the TARDIS, it connected itself to the computer and began transmitting adverts. One of these adverts had the food machine produce toast with written adverts on it. (AUDIO: Pop-Up)
Chris Parsons discovered a food machine, which he thought was a minibar, in the guest suite aboard the TARDIS. He set the dials to K12, but the food block he was served with tasted of steak and candy floss. (PROSE: Shada)
After the TARDIS was stolen by Thomas Brewster, the food machine was one of the items which he removed from the TARDIS and sold to the crew of the Gamma who were marooned on the Time Reef. Although the Fifth Doctor was unable to recover the original food machine, he told Nyssa that he could easily build another. (AUDIO: Time Reef)
The Fifth Doctor also used the machine to supply Erimem's cat Antranak with dead rat, much to his discomfort. (AUDIO: Nekromanteia)
Frobisher found the food machine and nearly filled the console room with Mars Bars. (COMIC: Voyager)
Flip Jackson used the food machine to make popcorn. (AUDIO: The Fourth Wall)
The Seventh Doctor asked Hugh and Janet for a sample of their cooking so he could program it into the food machine. (PROSE: Cat's Cradle: Witch Mark)
The Eighth Doctor's companion Sam Jones tried to order French toast and orange juice from the food machine, though she thought it looked like a Mars Bar and carrot juice. (PROSE: War of the Daleks)
Sam told the Doctor's other companion Fitz Kreiner that the TARDIS didn't have a kitchen, just a food machine. Fitz, who preferred making meals himself, found a kitchen, but wasn't sure whether Sam simply hadn't known about it, or if it had been created for him. (PROSE: Autumn Mist)
While travelling with Alexander Pope and Theobald, the Ninth Doctor threatened to restrict their access to the food machine's viennetta. (PROSE: Double Falsehood)
The Tenth Doctor tried to fix the machine, which had not been used in years. He failed and it produced food with disgusting flavours. He later used these food blocks to kill the Glutonoid. (COMIC: The Glutonoid Menace)
By the time that the Tenth Doctor was travelling with Rose-the-cat, the food replicator was still in disrepair and had begun to sprout mould. The Doctor noted it while creating a list of places in the TARDIS which were in need of a cleaning, although Rose-the-cat did not recognise the machine. (COMIC: A Rose by Any Other Name)