You ask about ‘ancient food,’ which is a pretty big topic, but I can address bread during the Roman Empire.

What kind of bread they ate depended upon the area. Today much of our agriculture is one of vast monocultures and very similar types of wheat are grown around the world. This was not true in ancient times, because there were many different local varieties of grains which were used for bread. Stephen Mitchell’s fantastic Anatolia: Land, Men and Gods in Asia Minor explains how rich Roman landowners would export their good grains to the cities while leaving the poor varieties for the rural inhabitants. Sometimes they used grains which we rarely use for bread nowadays, such as spelt.

There were also many regional variations for how bread was made. There were many different ways of preparing the flour and dough, and many different ways of baking bread. Just as an example the Roman writer Pliny in his Natural History details how the Gauls used beer as a leavening agent (yeast as we know it was unknown), while those in Picenum used fermenting grape juice (probably passum, or passito).

The end result was that bread was a very local affair. There was a rich variety of breads, due to regional types of grain, baking traditions and even leavening methods. Poorer rural people would have to make due with unleavened bread made from local inferior grains, while poor urban people had to live with cheap imported stuff for the dole. The rich, on the other hand, could have fantastic varieties of leavened bread. The Picentine bread was so famous that the satirist Martial even wrote about it.