Mocopan Coffee’s Babin Gurung goes back to basics to explore the variables of coffee grinder calibration and how to adjust a grinder.
That first cup of coffee in the morning after dialling in your grinder is often the highlight of many people’s day. If you’ve ever wondered why your afternoon coffee doesn’t taste the same, you are not alone. There is a reason why coffees taste better in the morning. Having fresh beans, a clean machine, and a well calibrated grinder makes all the difference. As the day progresses, you may not have all these variables in check. Beans go stale if you leave them in the hopper for more than two hours, which is why maintaining a minimum amount of coffee is the best practice. Your coffee machine can collect a lot of oil and grime from overuse, and if not cleaned regularly, can add unpleasant flavours in the cup. The best practice is to purge the group head and rinse the handle between use and backflushing after rush periods.
But what about grinder calibration? How often do we need to calibrate? Before I answer that, let’s look at what causes calibration to fluctuate.
Weather conditions: this one may seem odd, but changes in the weather have an immediate impact on grinder calibration. Coffee is a natural product and responds to environmental factors such as heat and moisture. This is why you will often see change in extraction time from morning to afternoon. To learn more, refer to Dr. Monika Fekete’s BeanScene June 2019 article on how grind temperature impacts extraction. Humidity plays a similar role. High humidity means the beans will absorb more moisture, making it harder to extract while drier conditions cause coffee to easily over extract. This change is more prominent in cafés that have coffee machines facing outside where temperature is inconsistent.
Coffee age: this refers to the batch or roasted date of coffee. Fresh coffee is high in moisture and carbon dioxide gas, making it harder to extract while older coffees are more porous and thus easier to extract. The ideal time to use a bag of coffee is between seven to 28 days from roast. When you switch from one batch of coffee to another, you will notice a change in extraction time. This is simply due to difference in moisture and carbon dioxide level. We don’t use coffee from the day before for calibration due to the same reason.
Hopper level: maintaining a minimum level of coffee beans in the hopper is important as it keeps constant pressure and encourages beans to pass through the grinder blades. Anytime the hopper is close to being empty, you will notice the grind will come out coarser, giving you a quicker extraction. This can be avoided by keeping the hopper about half-full.
Similarly, over heating of the grinder from repeated use, fluctuation of water pressure in your espresso machine, and inconsistent tamping can cause calibration to fluctuate. So, the answer to the question of ‘how often should you calibrate the grinder?’, is any time these variables change. The ultimate test is the taste itself. You should be able to recognise change in flavour these variables may cause. Refer to BeanScene’s article ‘What makes a coffee strong?’ from the August 2019 edition for further information on how flavours work.
Here is a breakdown of three flavour profiles you may encounter:
Under-extracted: if the shot runs faster than the ideal extraction time, it is considered under extracted. This means the water hasn’t fully absorbed all the desired flavours. You will mostly get acidic and sour flavour with a thin body. It may not necessarily taste unpleasant but there will be an obvious lack of sweetness. Visually, the crema will look pale and thin and may not hold for too long.
Over-extracted: this is the opposite of under-extracted where the shot runs longer than expected, allowing water to draw intense and harsh flavours. This can cause the coffee to taste bitter and leave your mouth feeling dry and hollow. Visually, it will look darker with thicker crema.
Well-extracted: This is when all the flavours come together making the coffee rich in aroma and flavour. This coffee should have higher sweetness and a well-rounded aftertaste. Visually, it should have deeper colour and the crema should hold for longer.
Now that we understand the variables of grinder calibration, let’s look at how to adjust the grinder.
Macro adjustment: this refers to the grinder adjustment we make once or twice a day. Let’s break this down into steps so it’s easier to follow:
Step 1: check your dose using a scale. Dose refers to the volume or grams of ground coffee that goes into a double group handle. This is dictated by your coffee recipe. For now, instead of fixing the dose button on the grinder, adjust the dose manually by adding or removing coffee by hand until you achieve the desired dose weight.
Step 2: check extraction time. Once the handle is loaded with the correct dose of coffee, press the double button and check the extraction time.
There are two things that can happen here. If the shot runs:
- Faster: it means the grind size is too coarse.
- Slower: it means the grind size is too fine.
The solution is to turn the dial towards fine to slow down the extraction time and coarse to speed the extraction time. The rule of thumb is every one line/notch creates two to three seconds change in extraction time. This is dependent on the age and condition of the grinder blades.
Let me explain how the grinder blades work. Underneath the hopper, there are two blades (burrs) which rotate to produce coffee grind. If the blades are wide apart, they produce coarser coffee and if the blades are close together, they produce finer coffee. The dial allows us to move the blades to produce the desired consistency of coffee. What’s notable is that every time you move the blades, it also impacts the amount of coffee that can pass through, resulting in an increase or decrease of dose amount. Since most automatic electronic grinders measure dose by grind time and not weight, going finer will result in a lower dose, and coarser will result in increased dose. Therefore, it is always advisable to adjust the dose button last once you achieve the correct grind consistency.
Step 3: a grinder holds some coffee in its chamber between the hopper and blades. For you to see the changed extraction time, you will need to flush some coffee first. This is dependent on the type of grinder you use but generally it’s between one to two shots of coffee. This will ensure the new grind setting is applied.
Next step: go back to step 1. This means, re-checking your dose amount to ensure you have the correct dose in the basket before checking extraction time again. Repeat the steps until you achieve the desired extraction time.
Final step: adjust the dose button on your grinder. Every grinder is different but, in most cases, every 0.2 seconds of adjustment on the grind time results in a change of one gram of coffee.
Micro adjustment: These are a series of small changes we make throughout the day to maintain grinder calibration. You may not necessarily use a scale for this, but making minor adjustments to the dial can help keep the extraction time within the parameters, ensuring the coffee tastes great all day, and not just in the morning.
This article appears in the February 2021 edition of BeanScene. Subscribe HERE.