Calibrating your commercial coffee grinder is something that should be done every morning prior to opening and should also be monitored throughout the day, particularly in erratic weather conditions. Many cafes and espresso bars ignore this procedure and the result is inconsistent and poor tasting espresso.
As coffee beans warm up, they expand and it is therefore much easier to extract their oils. If the coffee is a much cooler temperature, extraction is much more difficult. Remembering your correct extraction times you will find that the warmer the weather, the warmer the beans, the finer the grind. The cooler the weather, the more course the grind needs to be.
If you have high quality coffee beans, an excellent espresso machine, and a skilled barista, but do not have the coffee grinder adjusted for current conditions, the coffee produced can be of poor quality: either under extracted, which will taste sour, watery and weak, or over extracted, which will taste bitter and burnt. In fact, most often when you consume an espresso that is of poor quality, it is that the grind was set incorrectly for the atmospheric conditions at that time. No fancy latte art can hide a poor quality espresso.
The good news is that calibrating your grind is very simple to do. Unfortunately, many coffee shops and espresso bars don't bother to do it. The skilled barista can achieve the correct result purely by sight but for the rest, all you need is a kitchen timer. A timer with a digital readout, that has easy to read large numbers are best. You may want to get a kitchen timer with an adhesive back so it can stick to the front panel of your commercial espresso machine. This way, the timer will always be visible, and handy for checking your grind throughout the day.
There is a dial on all commercial grinders that turns clockwise and anti clockwise to adjust the way the blades or burrs, cut through the coffee beans. Which way you turn will determine whether the coffee is cut fine or course. The finer the grind, the smaller the granules, the slower the extraction. If the grind is too course, the granules are much larger and the water flows through the coffee too quickly. Over extraction vs under extraction.
Fresh Coffee vs Aged Coffee
Grinder adjustment is critical when using freshly roasted coffee and is a variable that needs to be taken into account when making espresso.
Coffee begins to emit carbon dioxide (de gas) immediately after roasting and can take at least 7 days before it begins to settle and become more stable. As coffee is a natural product, it can change quickly and dramatically during this de gassing process. Does this mean that the coffee cannot be used during this time? No. It certainly can but the grinder adjustment becomes more critical.
Coffee bags should always display the roasting date.
Optimal Extraction Times
When timing an espresso, the age of the coffee ie the roast date, should be taken into consideration. Also, most coffee roasters will advise on the optimum timing for their own particular roast. As a general guide, the optimal espresso should be approximately 30ml in length (including crema) and should extract for approximately 27-30 seconds.
* If the grind is correct, the flow of espresso will begin some seconds after engaging the programmed button
* Flow can be likened to a mouses tail, be rich and smooth and give a golden crema. You will notice the 'tiger stripe' on the surface of the crema
* Extraction should be 30ml over approximately 27-30 seconds
* If the coffee extracts too quickly, the grind is too course and will leave a sour taste on the sides of your tongue
* If the coffee extracts to slowly, the grind is too fine, leaving a burnt and bitter taste towards the back of your tongue
* Be sure to always clear the neck of your grinder of previously ground coffee when an adjustment is made so as not to mix the different grinds