A coffee grinder is at least as important for preparing good coffee as the espresso machine or brewing method itself. We therefore asked an absolute expert, Daniel Hofstetter, to break down the differences between espresso grinders, filter coffee grinders, and conical versus flat burrs for us.
Who is this article for: anyone who wants a solid overview of the differences and characteristics of coffee grinders. Reading time: 15 minutes. Author: Daniel Hofstetter, the author of this article, was the Swiss Filter Coffee Champion in 2017 and 2019 and finished 6th at the World Brewers Cup Championship. He has worked as a Global Product Manager and in research for the world market leader in coffee grinders.
Find out more about home espresso grinders here.
The Coffee Grinder: The Most Beautiful Ugly Duckling – A Relationship Guide
Switzerland is the best-equipped nation in the world when it comes to “home coffee equipment.” However, the coffee machine (whether a fully automatic or portafilter machine) is always in the spotlight. Today, we are turning our attention to its unsung hero: the coffee grinder.
Honestly: have you ever felt happy when the grinder focused and quickly dispensed the exact amount of coffee grounds into the portafilter...? On the flip side, every coffee geek has been annoyed a few times when the dose from the grinder fluctuated or the grind size just wasn't quite right. A few grams of expensive beans are quickly wasted. With this article, I would like to foster understanding and appreciation for these scorned stars of the coffee stage by looking under the hood and learning how to make the relationship work best.
The Grinding Mechanism – The Heart and Soul of a Coffee Grinder
A coffee grinder always consists of a grinding chamber where a moving, adjustable burr set grinds coffee beans and outputs the resulting coffee grounds through an opening for use. The grinding mechanism is operated manually or electrically, with the necessary power transferred via a shaft to the moving parts. As technocratic as this may sound, these are almost all the decisive characteristics that differentiate grinders or define their strengths and weaknesses, but let's take it one step at a time.
Application, Capacity, and Budget
The saying “look before you leap” also applies when buying a coffee grinder. If coffee lovers first clarify what the grinder needs to achieve, they will save themselves a lot of frustration. The following points should be decided at the start:
Which brewing method(s) must my grinder be able to cover? Should it grind coffee for espresso, café crème, filter coffee, or ibrik?
An espresso grinder can grind for espresso and potentially café crème. A coarser grind or the particle size distribution required for filter coffee is just as unattainable with a classic espresso grinder as it is usually unable to achieve the finer grind required for ibrik.
A shop grinder, however, might be able to handle everything from espresso or even ibrik to filter, but is significantly more complicated to handle than an espresso grinder.
So, if you know from the start how things will work in your coffee kitchen, you can already narrow down your search. And while we’re on the subject: make sure to plan your budget so that it covers more than just a dream coffee machine. On the contrary: your coffee quality will thank you if you save a little on the espresso machine and purchase a slightly more expensive grinder.
Simple household grinders often cannot keep up with semi-professional coffee grinders, and the extraction result will be disappointing!!
How much coffee is prepared with the grinder on an average day?
Regardless of the number of people using a grinder, you must consider how much coffee is to be prepared with the grinder and in what timeframe. A modern manual grinder can grind for espresso and filter coffee, can be taken on travels, and costs significantly less than an electric grinder. However, if a lot of coffee is being made and comfort is a priority, a manual grinder is generally not recommended.
When choosing a coffee grinder for the home, café, office, restaurant, or kiosk, one must consider not only the total volume but also its distribution over time. For a coffee grinder, it is the “peak hours” that burden the machine and subsequently annoy the barista.
The manufacturer's specifications for electric grinders usually include a load capacity (portions per minute). This specifies the duty cycle under which the motor does not reach a temperature that would damage it in the medium to long term, AND NOT the dispensing quantity/pattern that guarantees the barista a stable grind size or extraction.
How much money can I spend on a grinder?
Of course, all these considerations are useless if you don't keep your own budget in mind. This can potentially significantly influence the answers above or narrow down the selection options from the start.
For the commercial users among the readers: anyone who only looks at the purchase price is making a miscalculation… a coffee grinder must be understood as a wear-and-tear part in its entirety. By this, I mean that individual components (burrs, seals) wear out and must be replaced over time. Heavy users (i.e., really busy cafés) replace their grinders after 2–4 years at the latest. That is why they tend to check the so-called “total cost of ownership” (TCO) of a product for their purposes rather than just looking at the purchase price. TCO includes service costs, spare parts, and warranty services.
Types of Grinders
Shop Grinder
Everyone is probably familiar with the shop grinder. The large “tanks” behind the counter in supermarkets where you could grind the coffee beans you just bought... but of course, we don't do that because we want freshly ground coffee!
A shop grinder is characterized by its robust and simple construction. There is an “on/off switch,” a large grind adjustment range (usually from espresso to filter, sometimes even Turkish fine), possibly a bag holder, and an easily accessible bean hopper.
This doesn't sound or look incredibly sexy, but experimental baristas have discovered that certain models of shop grinders can indeed become winning grinders. The simplicity is captivating and allows for quickly grinding different (pre-portioned) coffees, so the user can easily switch from a rare espresso to an exquisite filter and work with the same grinder. The disadvantage is, of course, the workflow and the additional work steps (pouring beans in every time, pre-portioning, re-weighing).
Shop grinders have powerful, large motors and usually exhibit smoother operation than smaller models. This leads to a constant and precise grind.
Espresso Grinder (Doser)
The doser grinder embodies pure Italian espresso culture. The grinder functions exactly the same as an on-demand grinder. The only difference is that it grinds into a front-mounted dosing chamber, from which coffee is dispensed into the portafilter using a manual lever. The mechanical dosing chamber has a rotating star at the bottom of the chamber that ejects a specific amount of coffee grounds per lever pull using an adjustment screw. To this day, it is the fastest way to get (pre-ground) coffee grounds. An experienced barista can pull perfect espressos at a high-traffic bar, but as soon as the powder remains in the container for a longer time, we lose aroma, and if the grind size needs to be adjusted, you theoretically throw away a lot of coffee powder. These grinders are mainly still seen in Southern Europe today (Greece, Italy, Spain, Portugal) – they are very inexpensive and local roasters rely on them.
Recently, hybrid concepts have come onto the market, where the dosing chamber can only hold about 30g of coffee grounds, but it is “homogenized” (i.e., de-clumped) there and dispensed relatively well “leveled” into the portafilter without the annoying dosing fluctuations of an on-demand grinder.
Grind on demand
Real-time grinding on request is probably the more accurate description. The user starts the grinder via a button; it grinds for a pre-defined time, resulting in a relatively constant dose. The downside is that after every grind size adjustment, the grinding time must be adjusted, and the rule of three must always be used at the bar to minimize surplus (waste). Professional cafés and baristas weigh the portafilter before and after grinding and adjust the amount of coffee grounds as accurately as possible. While this slows down the workflow, it ensures that the specified brewing recipe can be adhered to precisely.
Grind by weight
The logical successor technology to on-demand grinders is called “grind by weight.” Instead of a timer that controls the motor run time, it is now a load cell. Finally, the user can set the desired amount of powder in grams and, depending on the quality of the system, receives a very constant and adequate quantity – regardless of grind size, bean density, or bean size. The technology is not yet fully mature. Many manufacturers struggle to eliminate the vibrations at the barista's workstation. Through sophisticated algorithms, they are trying to achieve tenth-of-a-gram precision. However, robust solutions are not yet on the market.
A side note: The resolution capability of a scale/load cell determines how precise and reproducible a measurement is. Just because a scale shows 2–3 decimal places does not mean it can weigh that accurately. Precision scales cost several thousand francs, and common coffee products are, at best, approximately precise. However, with the best baristas and sensory experts in the world, we have not been able to taste any differences in either filter or espresso that resulted from a 0.3g difference in dosage. So we should relax a little in this discussion!
Burr Geometries
There are two different types of burrs that are relevant in the market: conical burrs and flat burrs.
With conical burrs, there is usually a central cone with teeth milled into it (i.e., sharp edges of varying depth) and a surrounding ring that has a similar tooth pattern. Together, they form the grind gap, the distance between the burrs, which, together with the tooth depth, determines the grind size (i.e., the fineness of the coffee grounds).
In most cases, the central, conical part rotates. There are a few, newer models where the outer ring rotates. Both types have one thing in common: this geometry creates a relatively imprecise particle size distribution, because the coffee bean or its fragments cover a limited distance while being crushed, and the particles can be further shaped. This geometry requires more powerful motors than flat burrs but allows for lower speeds because the coffee grounds fall out automatically in the gravitational field and do not have to be thrown out centripetally.
Conical grinders result in a relatively high proportion of fine particles, which works quite well, especially with dark-roasted coffees that need to be extracted very briefly.
With lighter coffees that are also brewed for longer, this PSD is less clean, and that is why the industry in the premium sector is clearly moving away from this design.
Flat burrs usually consist of very similar or even identical pairs of burrs. Two rings, where one is stationary and the other rotates. The beans fall centrally into the grinding mechanism and are driven into the grind gap by centripetal force. The distance between the two burrs and their tooth depth also determine the fineness here. Flat burrs can be arranged both horizontally and vertically. In the latter case, a feed screw is required to drive the beans from the inlet of the grinding chamber forward and outward into the grind gap.
Flat burrs on the left and a conical grinding mechanism of the Baratza Sette 270wi.
We get a more discrete PSD from these grinders – especially with larger burr diameters and powerful motors with constant torque. That is why shop grinders usually perform very well. Unfortunately, these usually have a grind adjustment that is too poorly resolved to use them effectively in everyday life at the bar.
Burr Construction
Most burrs are manufactured on industrial milling machines from steel blanks; these computer-controlled cutting/milling machines cut large steel rods of 60–200mm diameter into discs, which are subsequently profiled.
The tooth pattern of a burr varies and includes 1–3 different teeth. The interplay of these geometries (depth, orientation, angle) is a science in itself, which is primarily “mastered by trial & error” in the industry today.
The material (steel alloy) and any possible coating (often titanium oxides or nitrides) determine the properties of the burr (hardness, coefficient of friction, thermal conductivity, durability) and have a not-to-be-underestimated influence on the aroma in the cup. To analyze this scientifically in a serious manner, more research is still needed. Until this happens, marketing copy continues to rule.
Grind Size / Particle Size Distribution
When we talk about grind size, we often mean two things: on one hand, the fineness or coarseness of the coffee grounds; on the other, the actual setting of the grinder on an arbitrary, model-specific scale.
Strictly speaking, the former is not correct; only the second usage makes sense. It should be noted here that every grinder (even if we have two identical models) must be viewed in isolation and, for example, grind setting 6 will never or at most only by pure coincidence have the same powder properties.
We will call these properties particle size distribution from now on. Because, as the word suggests, there is no homogeneous particle size. Coffee beans shatter stochastically (depending on chance) – no matter how good a grinder you use. The better the grinder, the more it “corrects” the stochastic chaos of the fragments and forces them into a discrete distribution of differently sized particles.
For physical reasons, in an ideal case, there is a distribution with 2 maxima – this means that on a distribution curve, we have 2 distinct accumulated particle sizes that characterize the powder. However, at every (!) grind size and with every grinder, there is always a colorful mix of particles ranging from a few millionths of a meter (micrometers, thousandths of a millimeter) to almost 2mm in diameter.
Now, why are we interested in this? Coffee is extracted with water (with the exception of industrial extractions, where other solvents are sometimes used). An extraction (substances are dissolved) takes place at the interface of the two media (water, coffee). The size and, derived from this, the surface area of the particles results in the contact area – this is always the case, whether we are making espresso or filter coffee! More surface area = more extraction... you guessed it: finer powder = larger surface area = stronger extract (expressed very simply and omitting other (disturbing) factors).
However, since we always have a messy mixture of particles of different sizes, it is difficult to maintain control over the extraction. That, in turn, would be good for being able to brew delicious coffee... One can suspect: the more precise the grinding, the “purer” the taste.
Many will cry out at this level of simplification – but for the sake of grasping the basics, we’ll leave it exactly at that.
Recently, with improved particle analysis possibilities, attention has also been paid to the influence of particle shape; initial findings are available but are not yet entirely conclusive.
To close the circle, it should be mentioned here: the mixture of different sized particles can also be felt as finer/coarser through our sense of touch. Finer powder offers more resistance to the brewing water (whether with or without the pressure of a pump) and leads to longer extraction times. Coarser powder consequently leads to shorter extraction times and effectively also fewer dissolved substances.
Performance Differences
The performance of a grinder depends on its motor and its burr. The motor operates the rotating burr via a shaft. With very hard beans (light roast, high density), it may happen that the motor cannot provide the necessary torque and the grinder blocks (instead of sand, there are now beans in the gears).
The burr and its rotational speed (diameter, tooth pattern, tooth depth) are decisive for the available grinding performance (grams of coffee powder per second).
While conical grinders usually have lower speeds, there is increasing suspicion that even for flat burrs at fine grind sizes (Turkish, espresso), a medium speed produces a better cup than high speeds. For coarser grind sizes (filter), the rule applies: the faster the better – because what must not be forgotten in this discussion: slower rotation means that the particles are mistreated longer in the grinding mechanism and the cumulative energy input (frictional heat, surface enlargement, motor heat) damages the coffee.
Once again, one must say: we still don't know everything by a long shot and continue to experiment happily. Some manufacturers even outsource this tinkering and offer grinders with variable speed under original marketing arguments.
Influence of Heat During Grinding
The topic of heat has been thrown into the room: It is clear that (roasted) coffee and heat do not get along well... when crushing whole beans, heating inevitably occurs – that is pure physics. But much more important is the efficiency of the grinder drive. If the motor heats up under load or has poor efficiency per se and generates a lot of waste heat, this leads to trouble – for the barista and the customer.
A Nature study <1> from 2016 explained this phenomenon better, which had plagued baristas throughout the day for years (shots run faster and faster, you have to set it finer and finer until nothing works anymore...). Roasted coffee is in a so-called glass state. Simply put, this means a pseudo-solid that gets different properties under heating – in our case, it shatters or is ground differently. This changes the PSD and the extraction and moves competition baristas to freeze their beans with liquid nitrogen in order to “grind” them into the smallest and most precise particles. You can imagine how practical that is in everyday life...
The Relationship Advice – 9 Tips for Happiness...
... a good coffee.
- Clean the bean hopper regularly – the oil from the beans dirties the plastic and goes rancid – not nice and definitely not tasty!
- Daily (for the café) or once a week (for the home user), “vacuum out” the empty grinder from both sides with a vacuum cleaner; this removes most of the powder residue.
- For the professional: at least once a week, open the grinding chamber and clean the burrs with a brush; coffee powder sticks in the teeth and becomes gross. Home users should do this about once a month, depending on volume.
- ATTENTION: Many manufacturers do not want customers to open the grinder themselves, and most products are (intentionally) not that easy to clean. This has to do with product liability and occupational safety.
- Therefore, the advice here: get professional training or keep your hands off – unfortunately, accidents keep happening where finger joints are severed or at least flesh wounds are caused!
- An alternative minimum solution is grinder cleaner and vacuuming.
- Never reach into the powder outlet with sharp objects. There is often a sensitive silicone membrane there that can be damaged. This serves for static discharge or targeted compaction of the coffee grounds and is a wear-and-tear part that must also be replaced during normal use.
- Choose the grinder according to your needs: this includes your skill, your brewing method, and especially your coffee throughput. Anyone who buys a weak grinder and grinds a lot of coffee will have no joy with every cup, every day, and through rapid wear of various parts.
High-frequency locations should have 2–3 grinders that can be used alternately during strong heating or if a replacement grinder is available in case of total failure. - The grinder (regardless of housing or buttons) is NOT operated with the portafilter (but unfortunately often hit with it)!
- Each grinder should be able to be tested with the respective machine – only then do you know for sure that it will be a happy couple – or a good threesome if you include the user with the hardware 😉
- Ask the manufacturer what an average life expectancy of burrs is. When they become blunt, the extraction worsens and the taste in the cup does too. The same warning applies to changing the burrs – only perform it yourself after professional training...!
- New burrs generally have a certain break-in period. Microscopic burrs on the sharpened blades must first be grated off until the grinder “settles” and grinds consistently.
- The way you treat your grinder, the grinder treats you... sounds cliché, but it is true; of course, masterful care cannot make the product better, but a brute can destroy any grinder in no time.
<1> https://www.nature.com/articles/srep24483
