How to adjust your coffee grinder

Mocopan Coffee explains why understanding and adjusting your coffee grinder is a key element in ensuring a quality extraction.
Coffee grinder

In the morning, after your work area is set up and you’ve got fresh coffee oils running through the group heads and group handles, the next stop on your journey to serving magic coffees to your weary-eyed, caffeine deficient customers is the grinder.

There exists a common belief that a barista should never touch the grinder. This is false. Coffee beans change with humidity and age, and the grinder blades change with wear over time. If a barista never touches the grinder, then their shots will slowly move further and further from where they should be. A good barista understands and adjusts the grinder regularly to maintain extraction perfection.

The concept of grind adjustment can be scary if it’s new, so let’s break it down. The grinder has a pair of blades that crush the coffee beans into powder. The closer the blades are together the smaller (or finer) the grind particle size will be. As the grind gets finer, the particles can be tamped closer together, making it harder for water to push through. This slows down extraction time.

The same theory works in reverse. Move the blades further apart, and the grind becomes coarser. These bigger particles, when tamped, sit further apart from each other, meaning water will move through quicker. This speeds up the extraction of espresso.

Think of it like straining water through small rocks, or straining water through sand. Water will move faster through the bigger pieces because there is more room for it to flow.

Getting the right grind is a balancing act. The first step is feeling if a grind is roughly accurate – it should feel powdery but with a gritty finish. If the powder feels very powdery and soft it is likely too fine. It the powder feels very gritty and rough it is likely too coarse.

Once the grind looks and feels right, the next check is running test shots and assessing the quality of the extraction. Never assess a grind setting using a single group handle; the shape of the double basket produces much more consistent shots.

There are many different philosophies on what makes a spectacular shot of coffee. A good general guide is that the first drop from the spouts should take four to six seconds and should drop like melted chocolate off a spoon. A decent extraction rate is 25 to 30 millilitres in 25 to 30 seconds.

If shots take less than 25 seconds, then the grind is too coarse and water is moving through it too quickly. The grinder probably needs to be adjusted to make the grind finer.

If shots take more than 35 seconds then the grind is too fine and water is moving through it too slowly. The grinder probably needs to be adjusted to make the grind coarser.

If you aren’t happy with an extraction, however, before adjusting the grinder, the first thing to do is run it again and concentrate on technique (dose, distribution and tamp). These are the most likely causes of a poor shot. If you run another shot and still aren’t happy with it, then you need to change the grind setting.

Adjusting the Grind
Different grinders have different adjustment dials, so start by checking your particular model and understanding which way to turn the dial to make the grind coarser or finer.

Only move the dial in very small increments of about three millimetres. If you’ve been monitoring your grind setting regularly, you’ll only ever need small adjustments. A three millimetre movement should change your shot time by three to five seconds, using the same dose and tamp technique.

To make the adjustment:
1) Decide what adjustment (finer or coarser) you require and move the collar. Make sure you have enough beans in the hopper and that the close slide is open allowing beans through to the blades.
2) Turn on the grinder for 10 seconds and discard that grind (it will still be on the old setting).
3) Run a test shot keeping dose and tamp technique consistent.
4) Assess shot quality and extraction rate (even if it’s not perfect, have you improved it?).
5) Repeat as necessary until correct extraction is achieved.

Electronic Grinders
Adjusting an electronic grinder requires an understanding of two variables at once: the dose and the grind size, and how changing one can influence the other.

The programmed dose grinds for a certain number of seconds to achieve a set dose (it doesn’t operate on weight). If your shots are not accurate, you must first determine whether it is the dose that needs adjusting or the grind size.

As a guide, once you’ve dosed and tamped the coffee it should be level on the surface and approximately five to six millimetres below the rim of the basket. If the coffee in the basket sits too low or too high then you should adjust the programmed dose time so the amount of coffee grind increases or decreases.

When changing the dose it’s best to increase or decrease in 0.20 – 0.30 second increments and test again. Assess the dose and the extraction and adjust again if needed.

If you dose and tamp and the coffee in the basket looks the way it should but the shot runs too quickly or too slowly, then you need to adjust the grind size.

When changing the grind size, be sure to move in small increments of about three millimetres. Then purge at least one or two shots and discard them so the change can take full affect. Then run another test shot and assess.

The tricky part of electronic grinders is that when you change the grind size, you are moving the blades closer together or further apart. By doing this you are also changing the amount that will grind in the set programmed dose time.

For example, if you make the grind finer, you move the blades closer together. If the dose time is set for five seconds, given the blades are now closer together, less coffee can pass through the blades in the same amount of time. The same is true in reverse. When you make the grind coarser, the blades move further apart, so more coffee can be pushed through.

This relationship is very important to understand when using electronic dosing grinders. Once you change the grind size you may need to change the dose time as well to compensate. The key to success is to always run test shots and find that perfect balance.

For this reason, when setting up an electronic grinder, it’s a good idea to start by free dosing and getting the grind setting right, then setting the dose times from there.

Like with all things coffee, it’s the small details that make the biggest difference. Pay attention to your grind setting daily, and tweak it as necessary, to make sure you are always putting magic in the cup.

This article was written by Habib Maarbani, former National Coffee Training and Development Manager at Mocopan Coffee.