According to Jewish custom, many congregations keep a barrel of beer in their synagogues for Shavout, their Summer Solstice Festival on June 6th. The story of why is both fascinating and a bit frightening.
It seems that when the Jewish people left Egypt and were at the foot of Mt. Sinai, God gave them an ultimatum according to one interpretation of the events: accept the Torah or get crushed by Mt. Sinai that He literally held over their heads like a keg of beer. Centuries later in the Middle Ages, a tradition emerged to keep a keg of beer in the synagogue to symbolize God’s ultimatum while the Jews stayed up all night to study until dawn.
Today, many synagogues have a keg of beer as part of their Shavout program.
Here’s a link to an article about it: