Evaluating the performance of a coffee machine is harder than it may seem. You need to know what makes a good drip coffee and according to Specialty Coffee AssociationThere are basic criteria for a good brew. Brewing time and water temperature are at the top of the list. Sizzling water should be in contact with the grounds for no less than four minutes and no more than eight. The ideal water temperature range is between 197 degrees Fahrenheit (92 degrees Celsius) and 205 degrees Fahrenheit (96 degrees Celsius).
We measure the temperature inside the brewing chamber of every coffee machine we test.
After brewing the coffee, we take readings of samples of the resulting coffee liquid using optical refractometer. Given the amount of water and freshly ground coffee used, this data allows us to calculate the total dissolved solids percentage of each brew. From this, we obtain the extraction percentage. The ideal range is considered to be between 18% and 20%.
We also confirm the measured data with a good old-fashioned taste test. Over-extracted coffee tastes bitter and harsh, while under-extracted coffee tends to be tender or sour. To be sure, we brew identical test batches at least three times to get an idea of the average results.
