In the United States each year, some 2 billion pounds of coffee is brewed using approximately 6 billion gallons of water. Because brewed coffee is comprised mainly of water (98.5% for brewed coffee and 95% for espresso), it has a direct influence on the quality of brewed coffee. It is therefore important to consider fully the quality of water to ensure the best possible coffee is brewed.
Pure water is a simple combination of hydrogen and oxygen. But we rarely encounter water in its pure form. Typically it contains many chemical compounds in an infinite variety of combinations and concentrations. Some of these materials, if present in significant enough amounts, can cause unusual tastes, odors and colors. These are referred to as dissolved (soluble) materials, because on a molecular level they are structurally part of the water. It often takes extreme methods of filtration to separate them.
Water may also contain undissolved (insoluble) material suspended in the solution. These may include living organisms (e.g., bacteria or molds), or non-living materials (e.g., fine dirt and sand). To ensure that water is safe for human consumption, municipalities are charged with removing the undissolved (suspended) material and chemically treating the water to destroy any harmful living organisms that it may contain.
Water is complex, and in the form we encounter it, typically contains varying amounts and types of other chemicals. The mineral balance in water interacts and reacts chemically and physically with ground coffee to produce the resulting extraction. Unsuitable water chemistry can over-extract or under-extract dramatically altering flavor and aroma characteristics. Changes in water composition will alter the flavor of coffee as much or more that water temperature variations or equipment quality. In addition to impacting flavor, poor water quality can have an unnecessary and undesired impact on equipment failures and malfunctions.
When water and coffee come into contact, water dissolves soluble substances in the coffee to reach physical and chemical equilibrium. These reactions affect the flavor extracted during the brewing process. Since the art of coffee brewing is in controlling the variables, water quality must also be controlled and held in balance to achieve a flavorful and consistent beverage. Remember that altering just one component of water (such as hardness) can change this equilibrium and alter the flavors that result from brewing.
