The six glasses are: beer, wine, spirits, coffee, tea, and Coke. I thought the title probably over-promised the contents of the book, but I was mistaken. The author does touch on the history of the world, through the lens of the six glasses.
The first three drinks contain alcohol, and the second three contain caffeine. The account of the first two relies a bit more on conjecture, given the age of the drinks and the scarcer historical documentation from those time periods.
I learned a lot about the drinks themselves, as well as about history. For instance, a naval officer by the name of Grogram made the first proto-cocktail when he commanded that sailors should drink their ration of rum mixed with some citrus juice and sugar. This concoction became known as 'grog' and gave the Brits an edge over the French navy, thanks to the presence of vitamin c in grog.
I gained a greater appreciation for coffee-houses and their association with scientific advances and free speech. Charles II tried to shut down coffee-houses when he ascended to the throne because they had provided a venue where the citizens could voice their opinions freely. He did not succeed. Coffee-houses were called 'Penny Universities,' because for the price of a cup of coffee you could gain an education (scientists would lecture there). Let's raise a cup of coffee!
I also gained a greater appreciation for Coke and its association with American democracy. Did you know that Coke went around the world on the tails of the American military during World War II? Coke was exempted from sugar rationing during the war because it was seen as vital to the war effort. Did you know the Arab world boycotted Coke for 30 years after Coke opened a bottling facility in Israel? Let's raise a bottle of Coke!
I would recommend this book to anyone interested in history or in drinking.