Coffee-brewing is as simple or as complex as you make it. At its heart, brewing coffee is the act of breaking open coffee beans and then exposing the grounds to hot water (extraction). The result is that organic compounds within the bean are absorbed into the water and coffee is born. It’s a simple chemical equation, with countless at-home experimentations and professional opinions.
People have been roasting and extracting the coffee bean for centuries, and you could travel the world focusing entirely on experiencing the different types of extractions that exist. In Ethiopia, where coffee is generally agreed to have been discovered, the coffee is roasted very dark over charcoals with frankincense perfuming the air, then ground fine and boiled in the djebeni pot, cooled a bit, and boiled many times at the brewer’s discretion. The result, thick at the bottom of the cup with fine grounds that sift through your teeth when you drink, is similar to the rich, spice- (often cardamom) scented brew of turkish coffee, made in the ornate czeve atop a fire or stovetop.
In Italy and parts of Europe there is the default extraction of espresso, rich, dark, oaky, coffee and hot water under pressure creating an entirely new experience of coffee. That espresso is paired with sweet milk or clouds of foam in the United States, and in many shops across the country is prepared differently: more volume, more acidity. Home espresso machines offer a similar experience. Sometimes espresso is poured over ice cream in the affogato, a dessert neither liquid nor solid and altogether marvelous.
At home, around the world, we are extracting coffee in all sorts of ways to enjoy together in kitchen-table rituals and homegrown hospitality rites. However you generally prepare your coffee, it always boils down (oops, bad pun, my apologies) to the same act of pulling coffee’s flavor compounds into water, and then enjoying it. Coffee-brewing is, as I said, as simple or as complex as you make it.
Good coffee, however, is the result of an alignment of a number of variables including the four most important: water quality and temperature, grind size, length of brew, and coffee-to-water ratio. Just isolating these four variables creates an immense amount of complexity, but paying attention is the first step toward brewing coffeehouse-worthy coffee at home.
Water Quality & Temperature
Coffee is at least 95% water, so it makes sense that it will have a huge influence on the final taste of the cup of coffee. For example: if your water has a chemical balance that emphasizes the flavor of copper, your mug o’ joe will have a metallic taste which may or may not be pleasant depending on your taste. For the precision-brewers out there, the Specialty Coffee Association of America, or SCAA, recommends around 150 ppm T.D.S. (Total Dissolved Solids), measurable by a small portable refractometer.
Temperature matters a lot too, when it comes to extraction, because heat increases molecular sensitivity and allows for better dissolution of the chemical compounds in the bean to the water. In fact, funky/sour or bitter coffees often result from respectively too low or too high temperatures when brewing. A general rule of thumb is to brew at 195-205 degrees Fahrenheit, or about 30 seconds off full, rolling boil.
Interestingly, many home coffee brewers (like the ubiquitous Mr. Coffee) heat the water to around 170 degrees Farenheit, immediately guaranteeing that no matter how fresh and delicious your coffee is, you will end up with an inferior cup. Try pouring heated water into the boiler, or purchasing a better model with variable temperatures.
The idea with grinding coffee is to increase the surfaces that are exposed to water, and to control it as much as possible while doing so. This is relatively simple: buy a good grinder (a Baratza burr grinder, like the one we use in our French Press and Chemex brew guides, is a great choice).
Finer coffee slows down brewing, resulting in more of the solubles being extracted into the water. In fact, if the coffee is ground too finely, the result will be “overextracted”: too much has been pulled out of the coffee, including the more unpleasant, bitter attributes of coffee. On the other hand, coarser ground coffee has less surface area for the water to touch and can result in “underextraction”, muddy and inarticulate coffee.
Even grinding is also important, so that you have the water extracting from each particle of coffee at the same rate and don’t end up with a cup combining all the worst bits of coffee flavor into one unfortunate mug! No grinder is perfect, but a quality burr grinder will do a much better job than the average spice grinder (which ‘flails’ at the bean, instead of cutting it).
Brew time, or contact time, works hand in hand with water composition, grind size, and coffee-to-water ratio to impact, again, which compounds are dissolved into the water. The ideal brew time will vary by the brewing method. For example, our French Press Guide recommends a 4-minute brew time, as does our Chemex Guide, while our Hario V60 (pour over) Guide recommends 2.5-3 minutes.
Flow rate, or how fast the water covers and passes the coffee, impacts the brew time, as does agitation (stirring) and filter type, along with the grind size. An easy fix is to adjust the grind finer if the coffee is flowing too fast, or looser if it is taking too long to brew. (If the grinds in your filter look like a silty swamp after brewing, you definitely need to loosen that grind.)
Coffee-to-water ratio is a sticky topic that can boil down to personal preference and that depends on the coffee and other factors such as the age of the coffee (how much organic compounds still remain). Recommendations vary, but a 1-14 coffee-water ration is on the strong side, and 1-20 is quite weak. (Note: the word “strong” is often mis-used in describing coffee to discuss dark roasting, or low-quality coffee. Really, it refers to how much coffee there is in the water.)
Coffee professionals tend to start with a brew ratio and measure the end result with a refractometer, giving a final T.D.S. count for how much of the coffee was absorbed in the water. We’re aiming for between 1.0% and 1.8% for drip or filter coffee, though the range most people tend to prefer is smaller: 1.15% to 1.35%. (Espresso ranges from 7%-12%, on average, and the concentration of coffee is why it tastes so strong.)
Taken together, these variables can be overwhelming. If, however, you take the time to focus on them one at a time, your brewing will improve drastically. More precise brewing almost always equals a better cup of coffee. And a better cup of coffee means happier friends, family, and self.