Article: The Sumerians were one of the first known beer drinking societies. Cereals were plentiful and were the key ingredient in their early brew. They brewed multiple kinds of beer consisting of wheat, barley, and mixed grain beers. Beer brewing was very important to the Sumerians. It was referenced in the Epic of Gilgamesh when Enkidu was introduced to the food and beer of Gilgamesh's people: "Drink the beer, as is the custom of the land... He drank the beer-seven jugs! and became expansive and sang with joy!"

Now answer this question: What was the key ingredient in early Sumerian brews?
Cereals