The SATs might have made you hate analogy problems, but this one sure is tasty.

That clangy thing taking up space in the bottom of your Guinness or Tetley’s can might soon be done away with and replaced by a coffee filter.

The ball inside the Guinness can, called a widget, contains a pocket of nitrogen gas held under pressure. When some lucky person opens the can, the pressure is released and the gas shoots out into the beer through a small hole and creates the foam.

You may now be thinking, Wait a minute—most beers seem to have plenty of gas bubbles even without some fancy widget. The thing is that Guinness and similar brews need the widget because nitrogen bubbles are smaller than those filled with carbon dioxide, the bubbling gas in other fizzy drinks. The small nitrogen bubbles make Guinness’ foam deliciously thick and creamy, but it’s harder to get the gas to come out of solution. The widget forces lots of excess nitrogen into the beer, setting off a well-timed bubble eruption.

But the widget is not the only way to send nitrogen bubbles cascading upward. In normal ...