Evaluating the performance of a coffee maker is trickier than it sounds. You need to know what good drip coffee is and, according to Specialty Coffee Associationthere are essential criteria for good brewing. Brew time and water temperature top the list. Hot water should be in contact with the yard for no less than four minutes and no more than eight. A good water temperature range is between 197 degrees Fahrenheit (92 degrees Celsius) and 205 degrees Fahrenheit (96 degrees Celsius).

To find out how well each coffee maker meets that challenge, we charted the length of their brewing cycles. We also use thermocouple heat sensors connected to industrial grade data loggers. That enables us to record the temperature inside the coffee grounds as brewing continues.

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After brewing the coffee, we take sample readings of the produced coffee liquid with a optical refractometer. Given that we factor in the amount of water and freshly ground coffee used, that data can calculate the percentage of Total Dissolved Solids in each brew. From there we come to the take percentage. The ideal range is generally thought to be between 18% and 20%.

We also back up the measured data with good old taste testing. Over-extracted coffee tastes bitter and sharp, while under-extracted coffee is often weak or sour. To be sure, we made the same test run at least three times to determine the average results.