I love the response that we receive for all of our blogs but no topic is more polarising than one that addresses grinder adjustment.
Like anything, calibrating your commercial coffee grinder is something that takes practice. Let me ease your mind a little. It's not as difficult as you may think. When I was first taught to roast coffee, I was told that the task was a simple process once I understood how coffee behaves. Once I understood this, it would become easier to understand the roasting process. It's no different when extracting coffee on an espresso machine and the theory is exactly the same when understanding grinder adjustment.
Quite simply, if you understand the 'why', then the 'how' is quite simple.
Checking your grind 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. I can't begin to tell you how many times I've been told...'the grinder was set up when we first opened our store and we were told never to touch it again.' If you ever wanted a reason why coffee is better or worse from one cafe to the next then here is exhibit A.
So here goes. Oils are extracted from ground coffee using heat and pressure and it's always going to be easier to extract from coffee if the beans are warm rather than cold. Coffee beans, like anything, constrict when they are cold and expand when they warm up so trying to make espresso with cold coffee will make life harder than it needs to be (hence the reason we don't store coffee in the fridge). Always use coffee beans at room temperature.
Now imagine this. If you had a glass filled with fine sand and another glass filled with larger pebbles and poured water into them both, the water would pass through the pebbles almost instantly while the same amount of water would struggle to pass through the sand. It's the same with coffee. The finer the grind, the slower the extraction, while the more course the grind, the faster the extraction.
Remembering your desired extraction time 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.
So...as time passes throughout the day, most often the weather conditions change and usually warm up. Therefore you'll notice that your extraction will become faster as the day progresses. This suggests that a minor adjustment to the fine side may be required periodically through the day.
If you are using quality coffee, 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 (extracted too fast), which will taste sour, watery and weak, or can be over extracted (extracted too slow), 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 conditions at that time. No fancy latte art can hide a poor quality espresso.
Fresh Coffee and Grinder Adjustment
Grinder adjustment is critical when using freshly roasted coffee and is a variable that needs to be taken into account when making espresso.
Coffee will emit carbon dioxide (de gas) immediately after roasting and can take at least 7 days before it begins to settle and become more stable. You'll notice a thick and almost bubbly extraction when using coffee in it's first few days after roasting and the extraction will be faster.
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. Although the true flavour profile may not be completely developed until after the degassing process.
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 and should extract for approximately 30 seconds depending on the size of your dose. Although, you may want to try different times according to your own taste.
* 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 around 25-30ml over approximately 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
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