The coffee bean is composed of millions of tiny cells full of highly soluble coffee goodness yet the cell walls themselves contain bitter compounds that fortunately for us are less soluble.
Proper brewing is designed to extract the more flavorful tasting components in the bean and then terminate the brew cycle before dissolving the unfavorable compounds into the pot. To accomplish this we try to match the grind to the particular brewer type and brewing cycle length.
Grinding is just a particle reduction mechanism of creating smaller bits to expose more surface area of the bean to make it easier for the brewing water to access the soluble solids distributed throughout the bean structure.
In raw coffee beans the cell walls are structurally ridged and maintain integrity to isolate each cell contents. Roasted coffee beans, on the other hand, are porous but only to a limited degree. The roasting process not only heats and transforms the cellular contents into coffee flavor compounds but also degrades and ruptures the cellulose cell walls therefore compromising the cells integrity.
In ground coffee the brewing water can easily dissolve the flavors from the fractured surface cells but can also leach the subsurface contents through the porous cell walls.
Coffee brewing is the process of selective liberation of the favorable cellular contents and hopefully leaving behind less desirable components. Fortunately hot water is a good vehicle for the extraction of miscible coffee oils, carbohydrates and caffeine but also good at softening and expanding fractured walls separating the cells.
Grinding exposes fractured surface cells directly to the hot water and also makes possible a route through deeper cells adjoining the exposed surface areas. The brew water flows into and out of these softened and fractured cells with impunity.
Coincidently and fortunately not all the constituents of coffee dissolve into the water at the same rate. The fortunate part is that the best stuff dissolves first and some of the more bitter and objectionable components dissolve more slowly. With this in mind you can understand why the correct grind size and length of brewing cycle work hand in hand to create the most favorable cup. The operative term is “over extraction.”
Consequently the length of the time for optimum brewing is dependent on grind size. Obviously a fine grind extracts quickly and a coarse grind takes longer. The method of brewing and the type of brewer will determine the best grind size and length of brewing cycle. When you read up on brewing the terms “dwell” and “bed-depth” will have relevance.
If you are new to home brewing of coffee, and if you don’t know the proper grind, you can consult the brewer instruction info sheet or ask a knowledgeable friend or even consult a coffee professional at Barista’s Roasting Company coffee shop for a start. Pre-ground packaged coffee is generally sized for home drip brewers. All grocery store grinders have grind icons to help the consumer but calibrations are only guides. Many grocery store grinders are out of calibration or just worn out. All coffee enthusiasts will eventually rub a little ground coffee between their fingers to ascertain the fineness of the grind. Fingers have lots of sensors and do a good job at determining if a grind is just right.
Be aware that all coffees don’t react to grinding the same way. Familiarity will be your guide. Degree of roast and country of origin and even coffee density will affect the taste of your coffee. If you try a pot ground a little finer and a pot a little coarser, you may find you have a different grind preference for that particular coffee. Decafs may require a different grind although nothing will improve the taste of decaf if it’s not a gourmet decaf.
Taste is a personal thing. Some people like strong coffee and some like it weaker. If you have tried many coffee origins you will find some are naturally stronger than others. This is another story for later but know that grind does affect the strength of brewed coffee. Coffee ground too coarse for your brewer will yield weak coffee brew. Too fine will make stronger tasting coffee but will also make it somewhat more bitter. If you grind it correctly for your brewer type and it is too weak you are likely not using enough coffee grinds. If your filter is not full just add another scoop as they say,” for the pot”.
By the way screen type filters and gold filters may require a slightly different grind than paper filters. Finer grinds will pass through the filter and make for a cloudy or murky brew. Check the bottom of your cup.
If you understand the principles – you can easily fine-tune the degree of grind and the amount of grinds to produce the best results for your pleasure.
There are four methods of grinding coffee for brewing: burr-grinding, chopping, pounding, and roller grinding.
Burr grinders use two revolving abrasive elements, such as wheels or conical grinding elements, between which the coffee beans are crushed or “torn” with little frictional heating. The process of squeezing and crushing of the beans releases the coffee’s etherical oils, which are then more easily extracted during the infusion process with hot water, making the coffee taste richer and smoother.
Both manually- and electrically-powered mills are available. These mills grind the coffee to a fairly uniform size determined by the separation of the two abrasive surfaces between which the coffee is ground; the uniform grind produces a more even extraction when brewed, without excessively fine particles that clog filters.
These mills offer a wide range of grind settings, making them suitable to grind coffee for various brewing systems such as espresso, drip, percolators, French press, and others. Many burr grinders, including almost all domestic versions, are unable to achieve the extremely fine grind required for the preparation of Turkish coffee; traditional Turkish hand grinders are an exception.
Conical burr grinders use steel burrs which allow them to grind effectively while rotating relatively slowly, usually below 500 rpm, reducing frictional heating of the ground coffee, thus preserving maximum aroma. Conical burr grinders are quieter and less likely to clog than disk grinders.
Grinders with disk-type burrs usually rotate faster than conical burr grinders and warm the ground coffee a little by friction, manual models less than electrical. They are cheaper than conical burr grinders, and are well suited for grinding small amounts of coffee (with no time for heat to build up) for home use.
A blade or propeller grinder
Manual Coffee & Pepper Grinders
Coffee beans can be chopped by using blades rotating at high speed (20,000 to 30,000 rpm), either in a blade grinder designed specifically for coffee and spices, or in a general use home blender. Devices of this sort are cheaper and longer-lasting than burr grinders, but the grind is not uniform and will produce particles of widely varying sizes where ideally all particles should have the same size, right for the method of brewing. The ground coffee is also warmed by friction.
Blade grinders create “coffee dust” that can clog up sieves in espresso machines and French presses, and are best suited for drip coffee makers. They are not recommended for grinding coffee for use with pump espresso machines.
Arabic coffee and Turkish coffee requires that the grounds be almost powdery in fineness, finer than can be achieved by most burr grinders. Pounding the beans with a mortar and pestle can pulverize the coffee finely enough.
In a roller grinder, the beans are ground between pairs of corrugated rollers. A roller grinder produces a more even grind size distribution and heats the ground coffee less than other grinding methods. However, due to their size and cost, roller grinders are used exclusively by commercial and industrial scale coffee producers.
Water-cooled roller grinders are used for high production rates as well as for fine grinds such as Turkish and espresso.