Even before people began farming in China, West Asia and Egypt, they were already using wild grain that they gathered to make beer. When they did begin farming, around 6,000 BC, they made even more beer. You make beer out of barley, which is a grain like wheat. You add yeast (like for making bread) to the barley, and water, and you let it sit, and it turns into beer in a few weeks. Or you can just mix barley and water and let it sit, and the natural yeast in the air will turn it into beer.
An Egyptian model showing beer jars,
from a Middle Kingdom tomb
There are a lot of advantages to turning barley into beer. For one thing, you don't have to worry about beer going bad, or getting wet, or mice eating it, anymore. Beer will keep a long time and still be good.
And if your water is no good, not clean, you can get sick from drinking it. A lot of people, especially children, died of dysentery from drinking bad water in antiquity. But the alcohol in the beer killed the germs, so beer was always safe to drink. (Most children in the United States today don't drink beer, but in antiquity and the Middle Ages children did drink beer).
Also, people enjoy drinking beer because the alcohol in it gets them tipsy! But people made fun of anyone who drank so much that he or she got really drunk.
Egyptian and West Asian beer was different from today's beer. It wasn't fizzy, and it was much thicker, almost like soup. People often drank it through straws. Pretty soon, people in other parts of Africa like Nubia and East Africa were also making and drinking beer, though sometimes from millet instead of barley.
In southern Europe, people mostly drank wine rather than beer. But in northern Europe, it's too cold to grow wine grapes (or it was in antiquity). Roman soldiers from the southern Mediterranean showed the Germans how to brew beer. So there, too, in Germany and Scandinavia and England, people drank beer or ale. In England, beer and ale were mostly made by women known as brewsters.
Sometime around 800 AD, people in the Carolingian Empire figured out that if you added hops (another kind of plant) to beer, you could make it keep longer. Mostly people didn't do this at first, because it made the beer taste bitter (the way beer tastes today) instead of sweet and fruity. Most people didn't like beer with hops in it. But by the 1200s AD most people in Germany drank beer made with hops, and by the late 1400s some people in England drank beer made with hops too.
For more about beer, check out these books from Amazon.com or from your library:
Spend the Day in Ancient Egypt : Projects and Activities That Bring the Past to Life, by Linda Honan (1999).
A History of Beer and Brewing, by I. Hornsey (2004). Entertaining, but also a lot of good information.
Ale, Beer, and Brewsters in England: Women's Work in a Changing World, by Judith Bennett (1999). Why women brewed the beer in medieval England, and why they stopped doing it.
Or check out this article on beer in the Encyclopedia Britannica.