Treating water to brew the perfect cup of coffee

BIRMINGHAM — In the article, "The pros and cons of water treatment for a perfect cup of coffee," featured in a previous issue of Water Technology, Cang Li, contributing writer, writes about how water can impact the flavor and quality of a steaming cup of coffee.

In the article, Li discusses findings from research published by British scientist Christopher Hendon at the University of Bath in the Journal of Agricultural and Food Chemistry by the American Chemical Society entitled, "The Role of Dissolved Cations in Coffee Extraction," on brewing the perfect cup of coffee.

"Hendon’s study explains why mineral content in water is important," Li shares in the article. "Hard water will generally produce a better tasting coffee compared to soft water; however, hard water will cause scale buildup inside the coffee equipment such as pumps, boilers and valves. This will increase long-term maintenance costs."

"In order to balance the taste of coffee and maintenance requirements for the coffee equipment," Li offers various pros and cons for different water treatment solutions:

Polyphosphate/siliphos treated water: A polyphosphate/siliphos filter only releases polyphosphate to the treated water in order to form a thin, protective layer on the metallic surfaces of the coffee machine. As a result, this technology inhibits scale deposition. There is no removal of chlorine and/or chloramine from tap water. Thus, polyphosphate treated water will not be a good choice for brewing coffee.
Distilled water: The distilled process will remove all dissolved solids, including minerals, and will keep all VOC (volatile organic compounds) and any gases in water (such as chlorine if distilled from tap). Since no minerals are in the water, this leads to under-extraction of coffee aroma compounds. As a result, the brewed coffee is flat. However, using distilled water will protect the equipment without scale out.
Reverse osmosis (RO) water: RO-treated water is close to distilled water and basically is a pure and corrosive form. There are no minerals, causing the coffee to taste flat. Although RO water can prevent scale, it will rust the equipment due to its aggressiveness. Since TDS is very low, this may cause the equipment sensor to stop functioning. A blending RO system has a built-in, by-pass tubing and a valve to mix incoming water and treated water, as well as provides a mechanism for the customers to dial in the precise TDS level to bring some hardness back and to make water less corrosive. Thus, if the cation concentration is right, blending RO water will make good coffee.
Softened water: Softening uses ion exchange technology to take out calcium and magnesium ions and introduce sodium ions into treated water. Therefore, softened water causes a flat taste for brewed coffee. Softened water will protect the equipment without scale out. A water softener itself will not remove chlorine and/or chloramine from water. Rather, chlorine and chloramine damages the resin beads due to its oxidation power.
Activated catalytic carbon treated water: Granular carbon, or carbon block filter, generally takes out bad odor and taste, such as chlorine and other organic contaminants, and leaves the minerals in treated water. This would be the ideal water for a perfect cup of coffee if hardness is not very high. However, this technology will not prevent the coffee machine from scale out.
Activated catalytic carbon with nano-crystal scale control: Except for the benefits mentioned above for activated catalytic carbon treated water, nano-crystal technology is to control the scale out. Although there is no change in the hardness concentration before and after treatment, nano-crystal formation significantly reduces scale deposition. The combination of catalytic carbon with nano-crystal scale control will balance the great taste and optimal coffee equipment maintenance.
Activated catalytic carbon with ion exchange scale control: There are mixed carbon and ion exchange resin bead products specially designed for coffee, tea and espresso applications. This technology improves not only bad odor and taste, but also reduces hardness in proper range. Therefore, treated water makes coffee taste great.
Bottled water: Commercially available bottled water could be from different sources and/or different water treatments, including tap water, spring water, RO, distilled and minerals. Spring bottled water can be hard or soft depending on the water sources. Mineral water is extremely hard and can make coffee bitter (over-extraction of coffee).