Pour a glass of soda or champagne and you’re likely to see a multitude of frothy bubbles, though the foam will quickly vanish. Pour a glass of beer and the foam will last much longer. In fact, according to Karl Siebert, who directs Cornell University’s brewing program, legend says that if you draw a little face in the head of a Guinness, it should still be there by the time you finish the drink. Siebert recently published a study investigating some of the factors important to beer foam: alcohol content, pH level and a barley protein known as barley lipid transfer protein 1 (LTP1) .

“You need some substances to stabilize the bubble walls in the foam to keep it around a long time,” said Siebert, who worked at the Stroh Brewery Company in Detroit for 18 years before joining the Cornell faculty.

Brewing scientists have known about some of the factors involved in creating lasting foam, such as carbon dioxide and compounds known as iso-alpha acids, for many years. However, research about the effect of alcohol content and pH are mixed. Some studies suggest high alcohol content promotes foam, while others suggest the key is low alcohol content.

Using both beer samples and a model system that mimicked beer, Siebert found that middle alcohol levels are actually best for foam, with middle levels being around 5 percent alcohol by volume (ABV). His experiments also showed that beer with a higher pH, around 4.6, would likely have better foam than beer at a lower pH, such as 3.8.

Siebert also found that the protein barley LTP1 is important to ideal foam, likely playing a greater role than some of the other barley proteins involved in creating the head on a beer.

“In most cases people want to have nice foam on their beer, and brewers work very hard to make it like that,” Siebert said.

Of course, once you’ve chosen the perfect beer, pouring it properly will ensure you make the most of its frothy qualities.

“It’s better to start out pouring down the wall of the glass until the glass is about half full, and then just start pouring into the center,” Siebert said. “That generates the foam and ideally leaves a nice foam head on the top.”