The Curious Barista's Guide to Coffee

by Tristan Stephenson

  HISTORY OF THE GRINDER

  Before the grinder there was the pestle and mortar. Both the Arabs and Ottomans highly revered a good pestle and mortar; wear was a sign of quality and very old and well-used examples could fetch incredibly high prices at markets. For a long time, it did the job just fine, but sooner or later basic mechanical mills were invented, probably in the 12th or 13th century, although it’s unlikely that they were intended for the sole purpose of grinding coffee. Consisting of little more than a dome-shaped stone that fits snugly inside a concave bowl, they were basically a mechanized pestle and mortar with a handle to affect the grinding action.

  The first purpose-built mills with moving metal parts probably emerged from Syria, specifically Damascus, in the 16th century. Damascus has a long history of making sharp metal objects, including its renowned toughened steel swords and knives which, along with coffee grinders, spread through the Ottoman Empire and beyond. These early grinders were honed in Turkey, where coffee drinking was especially popular. Turkish coffee grinders first made an appearance in the mid-17th century, and this early design set the blueprint for manual grinders for the following 250 years. Indeed, examples from this era aren’t dissimilar to today’s small manual mills that function as handy travel companions.

  These early Turkish grinders comprised two chambers, one on top of the other. Whole beans were placed in the top chamber and a handle was turned, milling the coffee and depositing it into the bottom chamber. The cutting implement in these devices was a precursor to the conical burr set, consisting of a stationary serrated hoop with a bevelled cone-shaped piece that fit closely inside. The cone would be mounted on an axis with a perpendicular handle connected at the top, which could be turned by hand to mill the coffee.

  The Turkish grinder later evolved into the French and English ‘lap’ mills, which worked under the same principles and usually collected the ground coffee in a wooden box with a draw for easy removal. One of the earliest European references to a coffee mill comes from 1665, when Nicholas Brook, ‘living at the Sign of the Frying-pan in St. Tulies-Street,’ London, advertised that he was ‘the only known man for making of Mills for grinding of Coffee powder, which Mills are sold by him from 40 to 45 shillings the Mill.’ Many variations of the same theme appeared in the 18th and 19th centuries. Some grinders were designed to fix to a table, while some effectively were a table; others were handheld, eventually becoming wall-mounted.

  The design of the cutter also evolved through this period, its evolution restricted only by the physical manufacturing capabilities of the time. At first, the early conical-style burr was cast with rough diagonal notches, but early 20th-century designs show lathe-cut pieces with two or three different teeth sizes of teeth. These models marketed themselves as being quieter, but it’s likely that they also showed good improvements to the uniformity of the grind size and the effort required to get there, too.

  Despite all this progress in grinding technology, it’s surprising to learn that the humble pestle and mortar was still held in very high regard right up to the mid-19th century. There can be no greater testament to this fact than the written approval of Jean Anthelme Brillat-Savarin, who conceded in his Physiology of Taste (1825) ‘the unanimous opinion was that coffee which had been beaten in a mortar was far better than that which had been ground’. It would appear that 19th-century baristas were not bereft of a certain sense of sentimentality.

  The first flat burr grinders have their roots in a coffee mill patented by Thomas Bruff, Sr. in 1798. The device used two fairly flat three-inch discs with large and small cutting teeth to mill the coffee down to size. For his troubles, Bruff , who actually worked as President Thomas Jefferson’s dentist (in addition to his job as a part-time coffee enthusiast) was actually granted the first U.S. patent for a coffee grinder.

  Adjustable grinders began to emerge through the early 19th century, and the American market in particular embraced them. American grinders of the time tended to be both of a larger capacity than European models and more numerous, reflecting the nation’s love for coffee in its early years. At the turn of the 20th century, the coffee grinder was, beyond all doubt, an indispensable piece of kitchen equipment across most of the US and Europe.

  The move towards motorized grinders (for a short time powered by steam but later on becoming electrical) made a coffee grinder a sound investment for the family home, since it could grind much finer, which people took as a sign that less coffee would be needed to make a brew. Mostly manufactured in Germany and France, the first machines for use at home appeared in the 1920s and were little more than manual grinders attached to a motorized belt. Operating at only 80–100 rpm (revolutions per minute), they would have been capable of grinding no more than 1 kg/2.2 lbs of coffee every 15 minutes! These clunky contraptions quickly blossomed into electrical artefacts of classic candy-coloured Bakelite, and some models even had two separate hoppers: one for grinding the Sunday-best coffee and the other for grinding lower-quality beans that had been padded out with malt or peas. The introduction of paper-filter coffee in the 1930s helped create a market for electrical grinders in the home, but pre-ground coffee and instant (soluble) coffee both emerged around the same time. Soluble coffee offered a more convenient, reliable, cheap and modern take on the coffee experience, and following on from the instant coffee of World War II, it quickly became the expedient method of coffee preparation in many countries, including the UK and the US.

  I’d highly recommend investing in a good grinder, as it will lead to much tastier drinks.

  A conical burr set can be seen at the top left of this picture, along with some flat burr variants.

  On a commercial level, much bigger grinders were conceived towards the end of the 1800s to meet the needs of large-scale roasters and retailers, and eventually even those who were manufacturing soluble coffee. Roller-style mills appeared in Germany with our old friend the Jabez Burns Company releasing its ‘Granulating Mill’ in 1872. Descendants of this type of grinder continue to service large-scale applications even today, and at the highest end they can process many tons of coffee in an hour.

  Higher-output grinders have generated new problems with overheating and clogging up, however. In response to this, manufacturers used larger burr sets to better dissipate heat, later on incorporating water-cooling into their designs. It would be these themes of heat and output that would drive the developments of grinder manufacturers through the 20th century, right up to present day.

  HOW GRINDING WORKS

  Grinding coffee is an altogether violent process, which takes its toll on the bean and eventually the grinder itself. Razor-sharp slabs of forged steel or toughened ceramic spin at 12,000 rpm, pulverizing, cutting, smashing and crushing coffee beans, before unceremoniously spitting the surviving fragments out for brewing. Heat generated during the process can damage coffee oils and can denature the fragile aromatics before they have a chance to make it into the cup. Factors like humidity, ambient temperature, roast degree and even bean density also play their part in how a grinder must be calibrated. To better understand how these factors can be mastered and what the best practices are for getting the most out of your grinder, we must first look at how coffee grinders work.

  BLADE GRINDERS

  There are some machines that masquerade as coffee grinders, but would be better put to use making a fruit smoothie. They are, in almost every way, no different to a blender, and the problem with a grinder like this lies in its tendency to smash coffee beans into inconsistently sized pieces, which ultimately makes for inconsistent extraction and sourness and bitterness in the cup. While blade grinders are a better option than buying pre-ground coffee, it’s far better to spend a little extra and get a burr grinder.

  BURR GRINDERS

  The burr grinder is made up of either two closefitting rings that have a series of angled cutting teeth notched into them, or a conical-shaped cutter that sits inside a ring of teeth. Burr grinders produce a more uniform grind size than blad
e grinders, which is good news for extraction. Burr grinders are available in both electrical and inexpensive manually operated models.

  The burrs must be adjustable, since every family of coffee brewer has design features that call for a specific brew time and grind size. An espresso machine demands finely ground coffee because it cannot achieve the necessary pressure that true espresso requires using coarsely ground stuff, just as a French press will provide poor filtration for very fine ground coffee, meaning that coarser is better. Setting (or ‘dialling in’) a grinder is an exercise in calibrating the correct grind size for the brew method and brew time, which hopefully rewards you with tasty coffee.

  On most grinders, the bottom burr is attached to the motor of the grinder and the top burr is moved vertically to set the fineness. Some grinders have stepped adjustment, meaning that the setting is dictated and constricted by numbered steps on the dial. Stepless grinders offer a greater degree of precision to the grind size, but that’s not to say that stepped grinders are inferior; it really depends on the setting of the step itself and the scope of grind size that the machine is designed to output.

  Burrs can be made from steel or ceramic. Neither is necessarily better and much depends on the intended use of the grinder. Ceramic has a lower thermal conductivity, so it takes a little longer to heat up than steel, but one could argue that steel dissipates the heat faster and cools quicker. Both steel and ceramic are prone to dulling over time, but steel tends to do so quicker, which can cause the cutting action to become more like milling. It never ceases to amaze me how much of an improvement to a cup of coffee can be achieved by simply replacing a set of burrs.

  The conical-shaped burr is shaped like a dollop of whipped cream protruding from the mouth of a conger eel. As the cone spins at 300–500 rpm, it creates a kind of whirlpool effect that, along with gravity, sucks coffee beans towards the large, ‘bean breaking’ segments that are responsible for the initial smash-and-stab action. Even in extremely fine or extremely coarse grinds, these first ‘curls’ of steel or ceramic do the same thing. As the bean fragments become smaller they are granted access to the next stage of the process, where the teeth become finer and the action more of a slice and a crunch. The grade of fineness is ultimately determined by how close the cone sits to the teeth at its base.

  Flat burrs consist of two rings that are slightly concave, positioned with cutting edges facing towards one another. As the bottom burr spins, the centrifugal force propels the beans towards the finer cutting teeth on the outside of the burr ring, which shoots the beans outwards towards the thin slit of space that determines the fineness setting. Flat burrs forgo the crushing action of conical burrs, creating a nibbling effect rather than a chewing action.

  One good thing about conical burrs is that adjustment is slightly more precise. This is because the cutting edges are not parallel to each other like they are on a flat burr. On a flat burr, the aperture between the two plates is directly proportional to the vertical adjustment of the burr – if you adjust by 0.5 mm, the plates will simply gain or lose a distance of 0.5 mm. On a conical burr, where the cutting faces are at around 60°, vertical movement of the adjusting burr will make for a smaller degree of separation between the burrs themselves – an adjustment of 0.5 mm will only move the burrs 0.25 mm closer, for example. This is a good thing. It allows for better precision when dialling-in the grinder. This is a moot point in the case of some modern grinders, where the adjustment is geared sufficiently to make fine adjustments very easy indeed, regardless of the burr type.

  UNIFORMITY OF GRIND SIZE

  Uniformity is all about how similar, or dissimilar, the grind particle sizes are from each other on any given grind setting. Different-sized pieces do things at different speeds, and the general rule of thumb is that halving the size of a coffee particle increases its extraction rate four-fold. If you cooked a quail egg, a hen egg and an ostrich egg in a (large) pan of boiling water for three minutes, the quail egg would be overcooked, the ostrich egg undercooked, and the hen egg about right. The same principles apply to brewing coffee.

  A broad range of grind particles is bad, as it means the very fine particles (‘fines’) overextract and the very large particles (‘rubble’) underextract. In an ideal world, every single particle of ground coffee would be precisely the same weight, and have precisely the same surface area as the next one. This pursuit of uniform grind size has been a hot topic in the speciality coffee industry for a while, with grinder manufacturers working hard to develop new ways of cutting up coffee into similar-sized pieces.

  The problem lies in coffee itself, mainly in the fact that it is brittle. When a coffee fragment is cut by a grinder burr, tiny pieces of the coffee dust fracture and splinter off – an unavoidable phenomenon that tends to be worse with darker-roasted coffees. These fines, as they are known, then easily get knocked through the burrs, exit the grinder, and become a part of the brew. Most grinders are thought to produce around 10 per cent fines in a typical sample of ground coffee. Fines are the infamous scourge of poor flow rate, uneven extraction and loss of body in espresso. They also cause overextraction and sludge in immersion brews, like the French press, plus they can stall filter brews by migrating downwards and blocking the pores in paper or cloth.

  Pieces of coffee bean that are larger than the average can also make their way out of the grinder. How exactly this happens is less certain, since the aperture created by the gap between the burrs should restrict the passing of larger pieces. It’s my belief that grinding, by its very nature, is violent enough to squash, extrude and propel larger pieces of coffee through gaps they wouldn’t normally fit through!

  Ultimately, the best grinders and best burr sets will increase uniformity and limit fines and rubble in the grounds. Using razor-sharp burrs is key, as it ensures that the beans are cut correctly and that minimal heat is produced during the cutting. The current poster boy of the coffee grinder world is the £2,400/$3,750 Mahlkonig EK43 grinder. Its unique burr set produces ground coffee that is not perfect, but it’s as close to perfect as we have managed to get so far.

  FINENESS

  The finer the grind, the higher the surface area of the coffee. Greater surface area means a quicker extraction, because the water has better access to the flavourful compounds that the coffee holds.

  For percolated coffee, where water lets gravity do the work and flows through a bed of coffee, the surface area needs to be relatively high. The first reason for this is that during percolation brewing the water has a limited contact period with the coffee. It washes through, extracting flavour as it goes. The second reason is that finer ground coffee acts as a barrier of hydraulic resistance during percolation, preventing the water from washing through and underextracting. In other words, a finer grind both speeds up and draws out extraction. A coarse grind means the water flows quickly through the bed of coffee, as well as having a slower rate of extraction. Getting the right balance means fine-tuning the grinder to reach a desirable contact period between water and coffee, and a grind particle size that corresponds to that contact period.

  When immersion brewing, with a French press, for example, the fineness of the grind affects only the rate of extraction, since the water and coffee contact period is determined by the person pushing the plunger. There is, perhaps, an exception where an excessively fine grind is used in a French press, leading to filter clogging, and rendering it impossible to depress fully.

  One of the biggest issues that the speciality coffee industry faces is the language and communication of grind fineness. It is perhaps the most important variable in brewing a cup of coffee and yet, even now, it is impossible for me to tell you how fine or coarse to grind your coffee. It’s not even possible to draw comparisons between identical models of grinder, since even minuscule deviations in the manufacture and assembly of the grinder will give rise to a subtle reworking of the grind size. In a properly equipped lab, it is of course possible to measure particle size (in microns) and to grade differ
ent samples accordingly, but for most of us this is not a day-to-day option.

  In this book, I refer to different degrees of fineness in words that describe how they might be used, i.e filter grind, Turkish grind. They are ambiguous phrases, highly inexact and only a few steps away from being utterly useless – this admission alone should illustrate the severity of the situation! The table opposite, however, may go some way towards helping you understand your grinder, so that you can get the best results possible in the cup. Please do not take it as gospel, however; part of the fun of making great coffee is tinkering with the grinder and analysing the shift in flavour. Note that the table is not linear, i.e. a coarse filter (6) is not necessarily the halfway point between filter (5) and coarse (7).

  GRIND SIZE DESCRIPTION

  1 Turkish – the finest coffee your grinder can produce without clogging up.

  2 Fine espresso – a very fine grind, probably with some clumping.

  3 Espresso – a fine grind, perhaps with some clumping, particularly when moulded into an espresso portafilter.

  4 Fine filter – somewhere between a filter grind and espresso.

  5 Filter – coffee grounds have a caster/superfine sugar texture, rather the finer powder of espresso.

  6 Coarse filter – similar to the fineness of granulated sugar.

  7 Coarse – immersion brewing territory, as coarse as large sea salt flakes.

  8 Very coarse – similar to the size of rock salt pieces, this grind is only used for long immersion brews.

  9 Chunks – large pieces of coffee shrapnel. Too big for normal brewing.

  TYPES OF GRINDER

  Some grinders are designed for espresso and others for coarser-ground filter or French press brewing. Espresso grinders tend to be specialists in the realms of fine grinding, allowing for very fine-tuning at the small end of the scale, which enables them to grind very fine coffee impressively well indeed. Grinders intended for grinding filter coffee operate over a much broader range of grind sizes, but tend not to go as fine as an espresso grinder. Some grinders, it seems, can fulfil both roles adequately, although I’d argue that a grinder designed for a specific purpose will generally produce better results than a jack of all trades.