Suntory Coffee’s grinder calibration calculations

Kyle Rutten of Suntory Coffee on grinder calibration and when you should be paying attending to the grind.
grinder calibration

When it comes to training, one of the biggest questions I get asked is: when should I calibrate my grinder? 

Calibration is simply the process of adjusting your grinder, moving the blades of the grinder closer or further apart, to ensure you get your desired outcome from the coffee. That outcome could be consistency or based on hitting a specific coffee recipe or hitting a specific taste/flavour.

For example, the dry weight of ground coffee is commonly referred to as the “dose”, let’s say 20 to 21 grams. The time it takes to extract the coffee (usually measured on the coffee machines screen or by using a timer) at 25 to 30 seconds pouring time and a yield of 40 to 44 grams.

Put in real life terms, the process of calibration would be to ensure the coffee in the above example stays within those parameters. The variables that affect the coffee (see Advanced calibration in the August issue) would determine how often the grinder would need to be calibrated. If your outcome was taste-based, you would adjust the grinder not trying to follow a specific recipe, but to maintain a specific flavour.

Following from my last article, whether you use a more sensory, manual approach to espresso extraction or are more process and numbers driven, you will need to adjust your grinder during the day. There are different times when this is more important than others, but it is your job as the barista to take control of the grinder and calibrate confidently to ensure the coffee is tasting at its absolute best throughout the entire day. 

This article on calibration will be focused on the main grinder used for your house blend. It’s great if you have two or more grinders pulling different blends or single origins, but for the purpose of this article I won’t be diving into tips for specific grinders such as the Mahlkönig EK43. 

Every grinder has its own specific method of adjusting the grinder plates. However, the main principles apply for all of them. Whether it is a small dial on the front of a Mythos 1 or the larger dial on the top of the Mazzer Royal Electronic, you need to move the dial in a clockwise or counterclockwise direction. This will cause the grinder plates to move closer (finer particle size) or further apart (larger particle size). 

Making the coffee grounds finer will cause them to become smaller, lighter, and make it more difficult for water to pass through once tamped. This will ultimately increase the time it takes to extract your espresso. 

If you make the coffee grounds coarser it will cause them to become bigger, heavier and make it more easy for water to pass through once tamped. This will lower the time it takes to extract your espresso. Your job as the barista is to determine what your end goal is (a specific recipe, or a specific taste) and adjust the grinder accordingly.

Let’s dig deeper into the best timing for grinder adjustment. 


Before you open your café, set aside some time to “dial in” the grinder. Dialling in is generally considered the very first calibration of the day. If it’s a restaurant that serves coffee in the evening then dialling in would occur before service starts. 

Dialling in usually takes the longest time compared to calibration needed later on. At this stage the equipment is usually cold, you’re working with a fresh bag of beans (different from the day before), and the temperature in the morning is usually very different then the rest of the day. Depending on your skill level and the variables working against you (see Advanced Calibration), dialling in could take one to 10 minutes. Many cafés take a numbers approach and use a scale and calibrate the grinder to a recipe. However, it is not uncommon for a café to simply use a sensory approach to calibrate the grinder based on the flavour they are aiming for. 

Whichever method you choose, make sure you are tasting the coffee too. 

• Warming up

As you start to dose coffee out of the grinder, the grinder plates begin to warm up and expand. Naturally, this causes the coffee to become more coarse.

Note: Most baristas will say that a large shift is required in the grind settings about 30 to 60 minutes after the grind has been adjusted in the morning. This is usually if your grinder is under the influence of the outside temperature, especially during winter after your grinder has reached peak operating temperature. 

• After every new bag 

While most roasters pride themselves on consistency, the reality is that coffee is a natural product. No matter how strict your quality control systems are, it is normal for a new bag of coffee to respond slightly differently to a grind setting and therefore require adjustment to keep the flavour and pour times constant. 

• Every hour or more 

Depending on the volume your café does, you should check and adjust the grind settings at least every hour. This rule generally works if you don’t do more than one kilogram of coffee every hour. As coffee sits in the hopper, it is exposed to oxygen, which is one of the biggest factors that influence coffee freshness. As coffee ages, even hour by hour, it will start to respond differently, and grind adjustments will be required. 

• Taste is off

When the coffee isn’t tasting right, you will need to make the grind finer and then courser to find that sweet spot. 

If you notice your shots are starting to run very fast or very slow – below 20 seconds and over 35 seconds are good indicators – you will also need to adjust your grinder. 

If the shot looks bubbly (gushing through) or thin and weak (channelling), it’s time to make an adjustment.

This article appears in the October edition of BeanScene. To read the story in FULL, subscribe now.

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