When Consumer Reports began hearing from consumers that their drip coffee makers were overflowing, sometimes spilling hot coffee and grounds on the counter, we decided to investigate. Were they putting in too much coffee? Too much water? Both?

To get to the bottom of the matter, we added a new test to our already challenging battery of brewing performance tests in an effort to duplicate the problem. We filled the filters to within ½ inch of the top, then added the maximum amount of water indicated on the machine. If the owner’s manual specified a maximum amount of coffee, we tried it that way, too.

The results were decidedly mixed. When overflow occurred, it ranged from spilling hot coffee onto the counter to sending coffee and grounds around the basket to depositing grounds in the coffee itself. The overflowing could occur at almost any point in the brewing cycle and not just at the end, as you might expect from a full carafe.

To flag the models that were more prone to spillover in our tests, we added a note to the model page for each coffee maker indicating whether it overflowed in our tests. Of the full-sized models we tested, about one-quarter overflowed, half sometimes overflowed, and the remaining one-quarter didn’t overflow. Our top-rated coffee maker, the Cuisinart PerfecTemp DCC-3200, $100, did not overflow. But another Cuisinart with good brewing performance, the Cuisinart Burr Grind & Brew DGB-700BC, $170, did overflow.

The one- and two-mug models we tested had a greater tendency to overflow as a group, with 60 percent doing so. The Black+Decker Single Serve CM620B, $35, overflowed in our tests. A better bet is the Technivorm Moccamaster Cup-One Brewer, which didn’t overflow but costs $220.

Mary Beth Brault, a spokeswoman for Hamilton Beach, which manufactures coffee makers, says the company helps troubleshoot overflow complaints. Circumstances that may cause the filter basket to overflow or the coffee maker to brew slowly include: a coffee maker that needs cleaning, excessive amounts of ground coffee, or too fine a grind. “Use slightly less grounds when brewing decaffeinated, flavored, or finely ground coffee," she recommends. "Or use medium-ground coffee.”

Sometimes it’s the filter that’s the problem, she adds. If you're using a paper filter, she advises rinsing the filter basket before inserting the paper filter, then making sure it’s completely open and in the proper position. And check that you haven’t accidentally used two filters instead of one.

If your coffee maker still overflows after taking these precautions, you may have to resort to brewing smaller amounts to avoid filling the filter basket to the rim. “If you want a stronger brew, make a smaller batch of coffee,” says Jim Nanni, associate director of appliance testing at Consumer Reports. “You just might need to brew additional carafes of fresh coffee, but being the coffee lover that you are, that's probably a good thing.” It’s a trade-off, but it's better than having grounds in your last gulp of coffee.

Shopping for a coffee maker? When you compare models in our full coffee maker ratings and recommendations, look on the model page in the Highs and Lows section for information on whether that model overflowed in our tests.