Coffee brewing masquerades as a simple process, when in reality it is a very complex interaction of many variables, all of which must be tightly regulated. Coffee gets most of its flavor from the great variety of chemical compounds released when the ground particles make contact with water. Under normal circumstances, water extracts roughly 80 percent of the available water-soluble flavoring compounds in coffee. This accounts for the brewed beverages aroma, taste, body and color. Altogether, these compounds are what we understand as the flavor of coffee.

Although small in relation to the total extract, the aromatic compounds readily extract during brewing, and account significantly for the perception of beverage flavor. The compounds responsible for taste (the ones that dissolve in water) and body (the ones that don’t dissolve) are more difficult to extract.

Why is extraction time so important? The total amount of material available for extraction changes, as does the proportion of each compound. Thus, the flavor changes continuously as time elapses. As a rule, the most flavorful compounds are extract first. The longer particles remain in contact with water, the greater the quantity of undesirable compounds are released.

The most desirable mixture of flavor elements occurs before the maximum amount of material available is removed. Consequently, for optimum results, the brewing process must be stopped before the point of maximum extraction.

Six Essential Elements of Coffee Brewing

1. Coffee-to-Water Ratio

Good coffee is a delicate balance between strength (solubles concentration) and extraction (solubles yield). A shift in the balance toward either one greatly affects the final brew. Strength: the most acceptable ranges of concentration fall between 1 and 1.5 percent coffee to 99 to 98.5 percent water. Coffee strength less than 1 percent is too weak. Coffee strength above 1.5 percent is too strong.

Extraction: the most acceptable rages of yield are between 18 and 22 percent. Underdeveloped brews (those 16 percent and lower) can be grassy or peanut-like. Over extracted brews (those above 24 percent) are found to be bitter or astringent.

2. Grind Setting

Your particular size – or, grind – plays a large role in the extraction of coffee. Select an improper grind setting for your coffee brewing, and you could be left with either an underdeveloped or an over-extracted beverage. As a general rule, longer brew times are paired with coarser particles, and shorter brew times with finer.

3. Equipment Operation

Brewing equipment often controls three important variables: 1) time of contact between grounds and water, 2) temperature of the water, and 3) turbulence during the brew process.

Time: it takes time for the water to dissolve and extract soluble material from the coffee grinds, and for that dissolved material to migrate into the beverage. As mentioned previously, water extracts different compounds in coffee at different rates, so the mixture of soluble material changes continuously and controlling brew time contributes greatly to optimal extraction and uniform, repeatable results.

Temperature: cold water doesn’t extract coffee as completely or as rapidly as hot water. But water that ranges from 195 to 204 degrees Fahrenheit liberates the aromatic materials rapidly and permits proper extraction of solubles in a reasonable time. As a general rule, seek a constant temperature throughout the during of the brewing process.

Turbulence: this refers to the mixing of water with the coffee grounds. Turbulence is necessary to pre-soak – or bloom – the coffee grounds, and then again to cause the water to pass through uniformly.

4. Brew Method

Different methods of preparation using the same coffee can result in very different taste and body characteristics. There are six basic methods used to extract the flavoring materials in coffee. Of the following, percolation and decoction are perceived to be too likely to over extract the coffee and lead to undesirable tastes in the brewed beverage.

Steeping: coffee grounds in a vessel are mixed with hot water and left in contact with the water for some length of time before separated from extract. (e.g., French press)

Decoction: loose coffee grounds are mixed in a container with water that continues to boil for some length of time (e.g., Turkish coffee). It usually results in a complete extraction due to the high temperate sustained (212 degrees Fahrenheit).

Percolation: coffee is placed into a container that is both the brewing chamber and the means of separating grounds from the beverage. A pump moves hot water through the coffee over and over. (e.g., percolator)

Drip Filtration: grounds are placed in a container that serves as the brewing chamber and means of separation from the brew. Hot water flows through the grounds only once. (e.g., manual pour over)

Vacuum Filtration: this method uses a two-chamber device to steep and then filter the coffee in either chamber. It is a variation of the steeping method. (e.g., siphon)

Pressurized Infusion: involves highly pressurized water (usually 9 to 10 atmospheres of pressure) forced through the coffee grounds, which are compacted into a small cake in the brewing chamber. (e.g., espresso)

5. Water

Since water can amount to more than 98 percent of the finished beverage, it is just as important to consider it as the coffee. Here are a few of the variables that contribute to water quality.

Total dissolved solids: an ideal TDS range is around 120 to 150 mg/L, and an acceptable broader range is 75 to 250 mg/L. Too few dissolved solids generally leads to ineffective extraction and will be unrefined or underextracted. Too many dissolved solids can lead to dull flavors and scale build up.

pH: this is the measure of acidity in water, which is derived from the concentration of hydrogen ions. A pH of 7.0 is neutral and ideal for coffee brewing. Above a pH of 7.0 means the water is alkaline and the coffee will be dull. Below a pH of 7.0 means the water is acidic.

Hardness: a measure of the presence of calcium and magnesium in water. Ideal hardness is around 70 to 80 mg/L. If the water hardness is too low, the coffee will lack structure. If the water hardness is too high, the coffee will be chalky.

6. Filtering

The brewed beverage will be quite murky unless something acts to separate the brewed grounds from the extract. Filters act to separate the insoluble materials from the brew, and as a result, has a direct impact on the body of the beverage. Filtering is often in the following form:

• Perforated metal plates – the holes allow extract to leave the brewing chamber yet hold back some of the fine particles in the coffee grounds. Perforated plates provide virtually no clarification of the beverage, enabling most fine and very fine particles to pass through.
• Woven wire screens – provide a greater number of smaller holes than perforated metal plates. The screens can be woven to hold back different amounts of the fine particles, but compared to the perforated metal plates, they offer only slightly better clarification of the beverage.
• Cloth – the type of cloth used and the weave determine its retentive capabilities. Very good beverage clarity can be achieved. The do require to be soaked and rinse, and may absorb oils that later decompose and alter beverage flavor.
• Paper – paper yields the clearest beverage. But users must take care during brewing not to impart any paper tastes to the brew. Poor quality paper filters may impede the flow of extract.