Desiring clean glassware for one’s craft beer does not make one a beer snob. Clean glasses are a basic right to be included in shelling out $8 for a glass of something thoughtfully and meticulously brewed by a dedicated team led by a passionate brewmaster who took the utmost care at every step. Proper cleanliness isn’t something that can be achieved by a dunk in the sink or even a run through the dishwasher, because both of those methods leave behind remnants. Remnants of what? Use your imagination: We’re talking about a detergent-laden dishwater.

According to Craft Beer’s eye-opening story, you can tell what’s really going on in there by the way bubbles behave in your glass. If they linger on the sides, especially in clusters, rather than floating straight to the top, they’re clinging to a particle of something. Depending on how far into it you’re willing to look, it’s your beer’s friendly way of alerting you that it’s not about to be consumed in its best light. Just as you’d send back a wineglass with visible “used” marks like a thumbprint or — gasp! — lipstick, sending back a beer whose bubbles indicate a less-than-crystal-clear situation does not a beer snob make.

Of course there are other markers: A chemical smell or taste, uneven or absent lacing of beer foam due to residue in the glass. But if you see a pack of bubbles loitering around, you can tell something fishy is up. Or soapy. Or, well, it’s dishwater, it’s something unpleasant. Read up on the finer points of serving beer on tap with the Draught Beer Quality Manual from the craft pioneers at the Brewers Association.

“Good beer quality depends on proper alignment of the dispense variables and consistent housekeeping practices,” the manual decrees. “As one industry insider quipped, ‘Even the Mona Lisa would look terrible in a museum with lousy lighting.’”