A coffee grinder is at least as important for making good coffee as the espresso machine or brewing method. That's why we asked Daniel Hofstetter, an absolute expert, to explain the differences between espresso grinders, filter coffee grinders, and conical and flat burrs for us.
Who this article is for: for anyone who wants to get a solid overview of the differences and characteristics of coffee grinders. Reading time: 15 minutes. Author: Daniel Hofsetter, the author of this article, was Swiss Filter Coffee Champion in 2017 and 2019 and placed 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.
You can find out more about espresso grinders for home here.
The Coffee Grinder: The Loveliest Ugly Duckling – a Relationship Guide
Switzerland is globally the best-equipped nation when it comes to "Home Coffee Equipment." However, the coffee machine (whether fully automatic or portafilter) always takes center stage. Today, attention is given to its stepping stone, the coffee grinder.
Honestly: have you ever been delighted when the grinder focused and quickly dispensed the exact amount of coffee grounds at the perfect grind setting into the portafilter...? In contrast, every coffee fanatic has been annoyed several times when the grinder's dispensing quantity fluctuated and the grind setting wasn't quite right again. A few grams of expensive coffee beans are quickly lost. With this article, I want to create understanding and appreciation for the overlooked stars on the coffee stage by looking under their hood and learning how to make the best of our relationship.
The Grinding Mechanism – The Heart and Soul of a Coffee Grinder
A coffee grinder always consists of a grinding chamber, in which a movable, adjustable grinding mechanism grinds coffee beans and dispenses the resulting coffee grounds through an opening for use. The grinding mechanism is operated manually or electrically; the necessary power is transmitted via a shaft to the movable parts of the grinding mechanism. As technocratic as this may sound, these are almost all the decisive characteristics that differentiate grinders or where their strengths and weaknesses lie, but one by one.
Type of Use, Capacity, and Budget
The saying "Look before you leap" also applies to buying a coffee grinder. If the coffee lover first clarifies what the grinder needs to accomplish, they will save themselves a lot of frustration. The following points need to be decided initially:
Which brewing method(s) must my grinder be able to handle? Should it grind coffee for espresso, café crème, filter coffee, or Ibrik?
An espresso grinder can grind for espresso and, if necessary, café crème. A coarser grind or the particle size distribution of filter coffee is not achieved with a classic espresso grinder, just as it usually cannot achieve the finer grind for Ibrik.
However, a shop grinder can, under certain circumstances, grind everything from espresso or even Ibrik to filter coffee, but it is significantly more complicated to handle than an espresso grinder.
So, if you know from the start how things should be in your coffee kitchen, you can narrow down your search. And while we're thinking: definitely plan your budget so that it's not just enough for a dream coffee machine. On the contrary: the quality of your coffee will thank you if you save on the espresso machine and buy 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, it must be considered how much coffee should be prepared with the grinder and in what time. A modern hand grinder can grind espresso and filter coffee, can be taken on trips, and costs significantly less than an electric grinder. However, if a lot of coffee is made and comfort is valued, a hand grinder is less advisable.
When choosing a coffee grinder for the household, café, office, restaurant, or kiosk, it is important not only to consider the absolute dispensing quantity but also its distribution over time. With a coffee grinder, it is the peak load periods ("peak hour") that cause problems for the machine and consequently annoy the barista.
The manufacturer's specifications for electric grinders usually include a load capacity (portions per minute). This indicates the load 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 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 significantly influence the above answers or limit the selection options from the outset.
For commercial users among the readers, however, it must be said: anyone who only looks at the purchase price has miscalculated... a coffee grinder must be understood as a wear part as a whole. 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. Therefore, they rather examine the so-called "total cost of ownership" (TCO) of a product for their purposes and not just 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 big "tanks" behind the counter in the supermarket, where you could grind freshly bought coffee beans... 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. It has an "on/off switch", a large grind adjustment range (normally from espresso to filter, sometimes even Turkish fine), possibly a bag holder, and an easily accessible bean hopper.
That doesn't sound or look particularly sexy, but experimental baristas have found that certain models of shop grinders can indeed become winning grinders. The simplicity is captivating and allows for quick grinding of 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, of course, is the workflow and the additional steps (inserting beans every time, pre-portioning, re-weighing).
Shop grinders have powerful, large motors and usually run more smoothly than smaller models. This leads to consistent and precise grinding.
Espresso Grinder (Doser)
The doser grinder embodies pure Italian espresso culture. The grinder functions exactly like an on-demand grinder. The only difference is that grinding takes place in a pre-positioned dosing chamber, from which coffee is dispensed into the portafilter using a manual spring lever. The mechanical dosing chamber has a rotating star at the bottom of the chamber, which ejects a certain amount of coffee grounds per lever pull via an adjusting screw. To this day, it is the fastest way to obtain (pre-ground) coffee grounds. A skilled barista can pull perfect espressos at a high-frequency bar, but as soon as the powder remains in the container for a longer period, we lose aroma, and if the grind needs to be adjusted, you theoretically throw away a lot of coffee powder. These grinders are still mainly seen in Southern Europe (Greece, Italy, Spain, Portugal) – they are very inexpensive and local roasters rely on them.
Recently, hybrid concepts have appeared on the market, where the dosing chamber can only hold about 30g of coffee grounds, but where it is "homogenized" (i.e., de-clumped) and dispensed into the portafilter relatively well "leveled" without the annoying dosing fluctuations of an on-demand grinder.
Grind on demand
Real-time grinding on demand would probably be the slightly cumbersome German term. The user starts the grinder via a button, which grinds for a previously defined time, resulting in a relatively constant output quantity. The disadvantage is that the grinding time has to be adjusted after each grind change and that the rule of three always has to be applied at the bar to minimize waste. Professional cafés and baristas weigh the portafilter before and after grinding and adjust the amount of coffee grounds as precisely as possible. While this slows down the workflow, it ensures that the specified brewing recipe can be followed accurately.
Grind by weight
The logical successor technology to on-demand grinders is called "grinding by weight". Instead of a timer that controls the motor's running time, there is now a load cell. So, finally, the user can set the desired powder amount in grams and, depending on the quality of the system, obtains a very consistent and adequate quantity – regardless of grind size, bean density, or bean size. The technology is not yet mature. Many manufacturers struggle to filter out vibrations at the barista workstation. Sophisticated algorithms are used to try to achieve tenth-of-a-gram precision. However, robust solutions are not yet on the market.
Side note: The resolution capability of a scale/load cell determines how precise and reproducible a measurement is. Just because a scale displays 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 differences in either filter coffee or espresso that resulted from 0.3g dosing differences. So, we should relax a bit 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 various depths) and a surrounding ring that has a similar tooth pattern. Together, they form the grinding 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. Common to both types is that this geometry results in a relatively imprecise particle size distribution, as the coffee bean or its fragments travel 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 rotational speeds, as the coffee grounds fall out automatically due to gravity and do not have to be thrown off centrifugally.
Conical grinders produce a relatively high proportion of fine particles, which works quite well, especially for darkly roasted and very short-extracted coffees.
However, for lighter coffees that are also extracted for longer, this PSD is less clean, and therefore, the industry in the premium segment is clearly moving away from this design.
Flat burrs consist of mostly very similar or even identical burr pairs. Two rings, one of which is stationary and the other rotates. The beans fall centrally into the grinding mechanism and are driven into the grinding gap by centrifugal 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 screw conveyor is needed to push the beans from the entry into the grinding chamber forward and outward into the grinding gap.
Flat burrs on the left and a conical burr grinder from the Baratza Sette 270wi.
From these grinders, we get a more discrete PSD – especially with larger burr diameters and powerful motors with constant torque. Therefore, shop grinders usually perform very well. Unfortunately, however, these usually have a grind adjustment that is too low in resolution to be effectively used daily 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 from 60-200mm in diameter into discs, which are subsequently profiled.
The tooth pattern of a burr is diverse and comprises 1-3 different teeth. The interaction of these geometries (depth, orientation, angle) is a science in itself, which today in industry is mainly "mastered through trial & error."
The material (steel alloy) and a possible coating (often titanium oxides or nitrides) determine the properties of the burr (hardness, coefficient of friction, thermal conductivity, durability) and have a not inconsiderable influence on the aroma in the cup. Further research is needed to scientifically analyze this properly. Until then, marketing jargon continues to dominate.
Grind Size / Particle Size Distribution
When we talk about grind size, we often mean two things: on the one hand, the fineness or coarseness of the coffee grounds, and on the other hand, the actual setting of the grinder on an arbitrary, model-specific scale.
The former is, strictly speaking, not correct; only the second use makes sense. It should be noted here that each grinder (even if we have two identical models) must be considered in isolation, and for example, grind setting 6 never or at most purely by chance results in the same powder properties.
We will now refer to these properties as particle size distribution. Because, as the word suggests, there is no homogeneous particle size. Coffee beans split stochastically (dependent on chance) – no matter how good a grinder you use. The better the grinder, the more it "corrects" this stochastic chaos of fragments and forces them into a discrete distribution of differently sized particles.
For physical reasons, in an ideal case, a distribution with 2 maxima is present – meaning that on a distribution curve, we have 2 distinct clustered particle sizes that characterize the powder. However, with every (!) grind size and every grinder, there is always a colorful heap of particles ranging from a few millionths of a meter (micrometers, thousandths of a millimeter) to almost 2mm in diameter.
Now, why does this matter to us? Coffee is extracted with water (with the exception of industrial extractions, where other solvents are sometimes used). Extraction (substances are dissolved) takes place at the interface of the two media (water, coffee). The size and derived surface area of the particles create 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 leaving out 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. This, in turn, would be good for brewing delicious coffee... So, one suspects: the more precise the grinding, the "purer" the taste.
At this level of simplification, many will now protest – but for understanding the basics, let's just leave it at that.
Recently, with improved particle analysis capabilities, attention has also been paid to the influence of particle shape; initial findings are available but not yet entirely conclusive.
To complete the circle, it should be mentioned here: the mixture of differently sized particles can also be felt by our sense of touch as finer/coarser. Finer powder offers more resistance to the brewing water (whether with or without pump pressure) and leads to longer extraction times. Coarser powder consequently leads to shorter extraction times and effectively fewer dissolved solids.
Performance Differences
The performance of a grinder depends on its motor and its burrs. The motor drives the rotating burr via a shaft. With very hard beans (light roast, high density), it is possible that the motor cannot generate the required torque and the grinder jams (instead of the proverbial sand, beans are now stuck in the mechanism).
The burr and its rotational speed (diameter, tooth pattern, tooth depth) are decisive for the available grinding capacity (grams of coffee powder per second).
While conical grinders generally have lower rotational speeds, the suspicion is growing that for flat burrs at fine grind settings (Turkish, espresso), a medium rotational speed results in a better cup than at high rotational speeds. For coarser grind settings (filter), the rule is: the faster the better – because what should not be forgotten in this discussion is that slower rotation means that the particles in the grinder are tortured longer and the cumulative energy input (friction heat, surface enlargement, motor heat) damages the coffee.
Once again, one must say: we are far from knowing everything and continue to experiment cheerfully. Certain manufacturers even outsource this playful aspect and offer grinders with variable rotational speed under original marketing arguments.
Influence of Heat during Grinding
The topic of heat has been brought up: it's clear that (roasted) coffee and heat don't mix well… when grinding whole beans, heating is inevitable – that's pure physics. But much more important is the efficiency of the grinder drive. If the motor heats up under load or inherently has poor efficiency and generates a lot of waste heat, this leads to trouble – for the barista and the customer.
A 2016 Nature study <1> better explained this phenomenon that had plagued baristas for years throughout the day (shots run faster and faster, you have to grind finer and finer, until nothing works anymore…). Roasted coffee is in a so-called glass state. Simply put, this means a pseudo-solid that acquires different properties when heated – in our case, it shatters or grinds differently. This changes the PGV and extraction and prompts competitive baristas to freeze their beans with liquid nitrogen to "grind" the smallest and most precise particles. You can imagine how practical that is in everyday life…
Relationship Advice – 9 Tips for Happiness…
… good coffee.
- Clean the bean hopper regularly – the oil from the beans soils the plastic and turns rancid – not nice and not tasty!
- Daily (for cafés) or once a week (for home users), use a vacuum cleaner to "vacuum out" the empty grinder from both sides, which removes most of the powder residue.
- For professionals: at least once a week, open the grinding chamber and clean the burrs with a brush; coffee powder sticks to the teeth and becomes disgusting. Home users should do this approximately once a month, depending on usage.
- ATTENTION: Many manufacturers do not want customers to open the grinder themselves, and most products are (intentionally) not easy to clean. This has to do with product liability and occupational safety.
- Therefore, here is the advice: get professional training or keep your hands off it – unfortunately, accidents repeatedly occur where finger joints are severed or at least flesh wounds are caused!
- An alternative minimal solution is grinder cleaner and vacuuming.
- Never reach into the powder outlet with sharp objects. Often there is a sensitive silicone membrane that can be damaged. This serves for static discharge or targeted compaction of the coffee grounds and is a wear part that must be replaced even with normal use.
- Choose the grinder according to your needs: this includes your skill, your preparation method, and especially your coffee throughput. Anyone who buys a weak grinder and grinds a lot of coffee will not be happy with every cup, every day, and due to rapid wear of various parts.
High-frequency locations should have 2-3 grinders that can be used alternately when heated heavily or have a spare grinder available in case of total failure. - The grinder (whether housing or buttons) is NOT operated with the portafilter (but rather, unfortunately, hit)!
- Every grinder should be testable with the respective machine – only then will 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 the average life expectancy of burrs is. If they become dull, the extraction will be worse and the taste in the cup will also suffer. For changing burrs, the above warning applies again – only do it yourself after professional training…!
- New burrs usually have a certain break-in period. Microscopic burrs on the sharpened blades must first be filed down until the grinder "settles in" and grinds consistently.
- As you treat your grinder, so the grinder treats you… it sounds cliché, but it's true; of course, masterful care cannot make the product better, but a berserker can destroy any grinder in no time.
<1> https://www.nature.com/articles/srep24483
