ST. LOUIS — Single Serve coffee makers, like Keurig machines, promise a fresh cup of coffee anytime you’re craving caffeine. Many of them look alike, but does that mean they can all brew the best cup?

Few (no?) kitchen appliances are as necessary as the drip coffee maker. Coffee makers need to do one thing: extract that sweet, sweet caffeine out of ground coffee into a drinkable cup of joe. But ...