A Czech Brewery’s Newest Employees Are 5 Crayfish

There are an endless number of decisions that a brewer can make about a beer recipe, but one ingredient—water—seems like it should be an afterthought. But even for the most basic, cheap beers, brewers pay a lot of attention to water chemistry. If it’s too alkaline, or full of minerals and other contaminants, it will impact the flavor of the final product. So they carefully test their water sources to make sure they’re good enough—and now one brewery in the Czech Republic has hired some tiny new employees to take over this task. They’re paid in food. Because they’re crayfish.

Crayfish, crustaceans that live on the bottom of streams, are considered an indicator species in the wild. Their absence from a waterway usually means that it is polluted. At the Protivin Brewery—brewers of the Platan family of beers—Reuters reports, they can show whether water pumped from a local natural source is safe to use. Five of the clawed arthropods have infrared sensors mounted on their backs that monitor their heart rates and movement. A portion of the water headed for the brew kettle is diverted to their tank, and if three or more of the crayfish have elevated heart rates, or start moving around a lot, a computer will tell brewers within three minutes that there’s a problem.

The brewery is working with scientists from the University of South Bohemia to develop this biosensor system, which they plan to continue upgrading. Cameras that can monitor the crayfishes’ hearts are a planned addition. The system remains experimental, so brewers still have to monitor water quality in a lab.