May 8, 2019

Gravimetric vs Timed Grinders: The Espresso Consistency Debate


The majority of high-end coffee grinders used for espresso dose by time, yet all official SCA standards are defined by weight. So, what’s the difference? Why do we keep using timed grinders? And how can we make sure we’re dosing accurately?

To answer these questions, I spoke with Lauro Fioretti, Product Manager at espresso machine and grinder manufacturer Simonelli Group, which includes brands such as Nuova Simonelli and Victoria Arduino.

Here’s what I found out.

Lee este artículo en español Espresso Consistente: Molino Con Temporizador vs. Gravimétrico

Lauro Fioretti (back) and 2017 World Barista Champion Dale Harris (front) checking for consistent espresso extraction.

Lauro Fioretti (back) and 2017 World Barista Champion Dale Harris (front). Credit: Victoria Arduino

What Are Timed & Gravimetric Grinders?

Let’s take an espresso recipe. This starting-point of this recipe is generally the ratio of dry, ground coffee that will go inside the portafilter to the beverage that will come out of the espresso machine.

Okay, but how do we define these amounts? By weight, volume, or something else altogether?

Lauro tells me, “In the Coffee Skills Program from the SCA, if you go to Barista Intermediate or Professional level, everything is measured by weight… The brew ratio, the recipe, everything is going by weight, not by volume.”

Yet on the market, we find both timed and gravimetric grinders.

A timed grinder will grind coffee for a certain time, one which has been set by the barista. Let’s say that a recipe calls for 18 grams of coffee. After testing, the barista discovers that 18 grams of ground coffee takes 5.8 seconds to grind. This, therefore, is what they set the grinder to.

A gravimetric grinder, on the other hand, measures the coffee’s weight as it drops into the portafilter. It turns the motor off when the pre-programmed weight (as set by the barista) is reached.

You might also like: How to Improve Consistency When Making Espresso-Based Drinks

The Mythos 2, a gravimetric grinder, in action

The Mythos 2, a gravimetric grinder, in action. Credit: Victoria Arduino

How Accurate Are Timed Grinders?

Grinders will always vary in their accuracy. The reliability, quality, maintenance, and degree of precision will have an effect on accuracy. (As Lauro says, the Black Eagle gravimetric espresso machine is accurate to 1 g, while the Mythos 2 gravimetric grinder is accurate to 0.1 g.)

Yet with timed grinders, we have to consider another factor: the relationship between weight and time.

Lauro says, “Every time you change one variable, automatically, [even] with the same time, you will have a different quantity. So if, for example, you are changing the grind size, so you adjust your grinder coarser or finer, it will result in a dramatic change in the amount of coffee… If you change the type of coffee, again, you change the amount of coffee that is delivered.”

Different grind settings take more or less time to grind. Different coffees will have different densities, affecting the volume and grind time. Baristas will need to recalculate grind time every time they change the coffee and recipe.

Yet this is not the only factor that affects the grind speed. Lauro tells me, “If the bean hopper is full or is almost empty… according to the amount of coffee you have on top of your bean hopper, you can have a different quantity of coffee that is delivered.”

With a full hopper, the weight of all that coffee will push the beans through the burr set, meaning that more coffee is ground more quickly. As more coffees are made and the hopper starts to empty, the pressure slowly decreases. With an almost empty hopper, you can actually see the beans bouncing off the blades instead of being ground: a symptom of the lack of pressure forcing them through.

Lauro tells me that he once put this to the test. “The grind size, temperature, all the variables were fixed, and we just tested the same grinder with a full hopper – a hopper full of beans – and the hopper almost empty,” he says, “and I saw with some grinders a difference up to 1.5 grams in the amount of coffee that was ground. This is not the case of the Mythos 1, for example, since it is much more accurate.”

Many of these issues are eliminated with a gravimetric machine; as Lauro says, “It’s a direct measurement… at the end, you will get your weight.”

But what can you do if you are using a timed machine?

Ground coffee being weighted on a digital scale.

Ground coffee being weighed on a digital scale. Credit: João Marcelo Stark

How Can You Ensure Consistency?

Ultimately, if you want to be consistent, you have to make sure you’re using the same amount of coffee every single time.

Lauro says, “If you want to be precise [and don’t have a gravimetric grinder], go with your grinder by time and then check your electronic scale… check the final product and adjust it manually. Of course, this takes time.”

It’s worth calibrating your scale on occasion, especially if you use more than one in the shop. Additionally, you may need to train your staff so that they efficiently and consistently use them.

Finally, be aware of clumping. Lauro says, “Ground coffee is difficult to measure because ground coffee has static electricity.” As a result, he continues, it “has a tendency to create clumps, so when you grind, because of the friction of the blades, it’s charging electricity to the grounds.

“And because they are very small – we are talking about microns – they tend to create clumps, so when they go out of the grinder… with the same time, some clumps can stay in or can go out, and can make some pretty big difference in the total output.”

The Mythos 2 has a “clump-crasher system,” but without this, even a gravimetric grinder may be marginally inaccurate due to clumps. So, if your equipment isn’t set up to avoid this, make sure you keep it in mind. If a dose has a large number of clumps, weigh it on electric scales.

Consistent espresso extraction using a naked portafilter

Pulling espresso with a naked portafilter. Credit: Victoria Arduino

Consistent, accurate espresso shot dosing is critical for both well-extracted espresso and customer retention rates. So, understand your equipment. Know if your grinder is timed or gravimetric. Use a scale if you need to, and make sure to calibrate it regularly.

Remember: a gram of difference can have a big impact on the consumer experience.

Please note: This article has been sponsored by Simonelli Group.

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