The love-hate of water and coffee brewing: Part One

April 15, 2011

The impact of water on coffee and brewing equipment.

Whether it’s to perk up in the morning or for the sheer enjoyment of the taste, many Americans depend on at least one good cup of coffee to get the day started on the right foot. According to the National Coffee Association, one half of all Americans consume coffee every day. And, this consumption is fairly stable — 84 percent of consumers say their coffee habits have not changed in the last six months in response to the economy.

While drip coffee is by far the most common coffee beverage, specialty espresso beverages are driving away from home consumption. After water, coffee is the second most widely-consumed beverage in the world.

There are a number of differences between espresso brewing and drip coffee, but both have water as the primary ingredient. Coffee is about 98.5 percent water and espresso is about 85-96 percent water. However, water impacts each type in different ways.

Brewing a perfect espresso beverage requires the proper management of a number of variables, including the grind of the bean, the dosing, the temperature of the water, the brewing pressure, the tamp pressure, the extraction time and the mineral content of the water (and of course, the blend of beans, the roasting, the quality of the espresso machine and the skill of the barista). Even the temperature of the portafilter and basket are important, which is why the portafilter is left in the group head of the espresso machine even when shots aren’t being drawn. Each of these determines whether the espresso shot will be bitter, sour, weak or strong.

Drip brewing is far less labor intensive and more forgiving, but still requires a certain grind, the correct temperature (typically 190-205 F) and the proper extraction time.

Tap water’s effect on coffee

As you know, tap water is a complex solution of chemicals, organics and minerals, and has pH and alkalinity characteristics. Each of these has an effect on the quality of coffee-based beverages.

Total Dissolved Solids: During the brewing process solids are extracted from the coffee grounds and without consistent TDS levels the quality of coffee and espresso can range greatly from strong and bitter to weak and underdeveloped. Without controlling the TDS level the consistency of the beverage will vary. Low TDS (<50 ppm) can result in a bitter or tart tasting coffee and espresso. High TDS (>500 ppm) could mean that sodium, calcium, chloride and magnesium are detectable in the final product. Also, high DTS saturated water will not extract at full strength as there is no space left to add the finest of the coffee.

Total Hardness: Hardness ions, such as calcium and magnesium, bind with the extracted coffee bean organics from the brewing process to give the correct flavor to the coffee and espresso beverages. Minerals also help to reduce the acidity of water. Without the proper amount of hard mineral your coffee will have a high level of astringency or be very bitter.

pH: Water below 7.0 is acidic and corrosive, water above 7.0 is basic and caustic. Natural low pH indicates a lack of mineral in the water, so water will taste flat or bitter (it’s like drinking distilled water, which has a pH of about 5.5). As pH increases (>7) the result is an astringent taste. Higher pH also usually indicates a higher alkalinity and possibility of limescale. Due to the fact that a person with sensitive taste can notice a pH shift of as little as 0.1, controlling your pH is vital to consistency and taste. The ideal is a pH of around 7.

Alkalinity: High alkalinity is a catalyst for scale development in the brewing equipment.

Total chlorides: Elevated levels of total chlorides are most commonly associated with salt. In normal levels, chlorides will result in a sweet taste to brewed beverages, but at elevated levels can cause sourness. Chlorides are also especially corrosive on stainless steel, quickly eating away at exposed components.

Chlorine: Chlorine can alter the aroma and taste of coffee/espresso by oxidizing the aromatics and oils, reducing the pH balance and imparting chemical/medicinal odors and tastes. Chlorine readily bonds with organics to create compounds that can impart an "earthy or moldy" tone to coffee. In addition, chlorine causes corrosion on metals and can cause brittle o-rings and gaskets (quality commercial espresso machines use Teflon gaskets, especially at the boiler, which helps to reduce chemical-induced problems).

Particulates (dirt, sediment, ferric metals, organic material): These cause plugging of orifices and abrasion on surfaces.

Water and extraction time

There are generally three differences between espresso beans and coffee beans: Espresso beans are roasted longer to bring out the bolder flavors (which is why they’re darker), they’re ground much finer (almost to a powder consistency) and there is a much shorter extraction time, around 25 seconds. If the extraction is too long — say, 35 seconds — too much of the bitter oils will be drawn out from within the bean, and the drink may taste burnt. If the time is too short — say 15 seconds — the beverage will be under extracted resulting in weak, sour espresso and little crema that will quickly dissipate.

Crema is the golden brown foam-like layer on the surface and indicates a properly brewed shot of espresso. If the crema is dark brown, the water passed through the tamped coffee too slowly. If the crema is too light, the water passed through too quickly. The perfect espresso shot should be like a light maple syrup, have a layer of dark brown crema and taste sweet.

Time, pressure and temperature

Time, pressure and temperature will make or break a good espresso shot, and the quality of the water impacts all of these factors.

Time: Even with a perfect extraction time in seconds, a poor shot can result because of clogging in the tubing, ports and other parts due to scale. For example, the group head has a part called a gicleur. This limits the flow of water to the basket. If it’s scaled, it could reduce the flow too much, resulting in a poor pre-infusion and under extraction. Pre-infusion is when the tamped coffee is made wet, followed by a brief pause, before the actual brewing process begins. This helps to seep water through the coffee evenly so it doesn’t channel. If there’s uneven water flow, the resulting espresso will be under extracted and weak. If the espresso stream is not centered when coming from the portafilter, or there are multiple streams, channeling is occurring.

Pressure: To "pull" a shot, there needs to be about 9 bars of pressure. Scale in the boiler can reduce this pressure over time. Without the proper pressure, the shot will be weak, thin and watery.

Temperature: Scale or corrosion on the probes, elements and heat exchanges can make it more difficult to get the high temperatures required both for extraction and for frothing the milk.

Brewed coffee is really just steeped coarsely ground beans. Extraction time for drip coffee is typically four to five minutes. With drip it’s important to avoid swelling of the coffee grounds due to too long of an exposure to the heated water or too low of a temperature which results in poor extraction of the oils. This could be caused by under filling of the reservoir due to an inlet valve that is stuck closed or leaks due to damaged gaskets, o-rings or cracked tubes. It could also be the result of a scaled temperature probe.

Water is the primary ingredient of coffee beverages, making up over 98 percent of the product. It can have a significant impact on the brewing cycle and ultimate taste of the final product. A certain amount of mineral in the water is necessary to produce a pleasant flavor and to aid the extraction of oils from the coffee bean. However, certain minerals make the water hard," which can be good and bad for the beverage. To ensure consistently great-tasting, premium water, filtration is the best solution. We’ll pick up the discussion in the next issue with part two.

Roy E. Parker is the senior marketing manager for Pentair Foodservice, which includes the brands Everpure and SHURflo. He’s been with Pentair for five years and has helped to launch new products, including the Claris softening and filtration systems and the award winning MRS 600 HE and HE II high efficiency reverse osmosis systems, and new tools, such as the SMARTWORKS™ and SMART OFFICE WATER interactive water testing and analysis programs.

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