Few sights are as satisfying as that of a dark, creamy Guinness resting atop a few inches of lager or ale. But what keeps those delicious layers separate?

IT'S BEER PHYSICS!

While stouts like Guinness may look and taste richer than other beers, their actual molecular density is lower. Poured correctly (more on that below), the Guinness in a Half and Half will float like a delicious cloud above its denser golden counterpart.

The trick here is perfecting the pour. Filling the glass too quickly can force the beers to mix, which is still delicious but not as visually impressive. There are two primary methods for preparing a great Half and Half: with spoon and without.

WHEN THERE IS NO SPOON

Hold a pint glass at an angle and fill it 2/3 of the way with Harp or another lager. Don’t be afraid to get up a good head of foam. Wait for the head to settle down, which should leave your glass about half-full (or half-empty; we’re not judging). Pour your Guinness slowly but steadily over the top until the glass is full.

THE SPOON METHOD

Repeat the first two steps above. Grab a tablespoon and tilt it into the glass so the tip hovers just over the layer of lager. Pour your stout slowly but steadily over the spoon, keeping the stream centered in the glass as much as possible.

Repeat as necessary for the thirsty friends who have gathered to watch you pour drinks.

There’s a lot to learn—and love—about Guinness. For more answers to questions about your favorite brew, check out mental_floss’s Big Questions channel—preferably with a Guinness in hand. (But please remember to drink responsibly.)