What is “Nitro”?
“Nitro” stands for nitrogen, a gas that makes up most of the air we breathe. At a bar, brewery, or brewpub, “nitro” is a mixture of two gases: nitrogen (75% of the mixture) and carbon dioxide (25% of the mixture). This blend is known as “beer gas.”
Normally, straight carbon dioxide is the gas used to carbonate beer. Unless you are drinking a “nitro beer” the bubbles in your beer are carbon dioxide. It’s the difference in size and stability of the bubbles between nitrogen and carbon dioxide that makes for the difference in mouthfeel. Since nitrogen has smaller bubbles than carbon dioxide, the mouthfeel of a “nitro beer” is creamier and more silky. Nitrogen bubbles are also more stable, which provides for a thicker head on the beer.
Finally, “beer gas” lacks the carbonic acid bite that straight carbon dioxide imparts in beer. Without the bite, “nitro beer” tastes maltier, which is why “beer gas” is typically used to serve maltier styles.