Commercial Coffee Makers: The Science of Brewing the Perfect Cup of Coffee

Coffee Brewing Basics

To brew the perfect rich and steamy cup of coffee, you first need to know the basic elements of brewing. There are six major factors that affect the flavor and extraction of your coffee: water, temperature, time, turbulence, filtration, and cleanliness. This section will outline each of these elements and explain how to perfect each of them.

Water

Pure, filtered water aides in producing the best tasting and smelling coffee every time you brew. Clean water is key in the process because water makes up more than 98% of the coffee in your cup. When the water in coffee has a high mineral deposit content, it can negatively affect the taste of your coffee. To ensure that you receive the most aesthetic cup of coffee possible, the water used in brewing should not exceed 50-100 ppm (parts per million) dissolved minerals; however anywhere below 300 ppm will produce an acceptable cup of coffee. To ensure the water you use remains clean, you should inspect your brewer frequently and make sure it is free from contamination and odors.

Temperature

The water temperature will affect the flavor and extraction of each cup of coffee you drink. Ideal water temperature should stay within the range of 195 degrees Fahrenheit to 205 degrees Fahrenheit or 92-96 degrees Celsius. Water that falls below this temperature will negatively affect the savor of each cup.

Time

Depending on the amount of time that each pot of coffee is brewed and the amount of time the water is in direct contact with the coffee grains, the flavor can either be enhanced or reduced. If the coffee grains are in direct contact with the water or is brewed for an excessive amount of time, the flavor and aroma of the coffee will dramatically decrease, causing the cup to become “watered down.” In contrast, if the coffee grains are not brewed or in contact for long enough, the coffee will have a strong flavor and aroma that might prove offensive to some people.

Turbulence

When water passes over and through the coffee grains, turbulence is created which causes the particles to separate. When particles separate, a uniform flow of water is produced around the grains, allowing perfect extraction to occur. When proper extraction occurs, the result will be a tasty and aromatic cup of coffee each time.

Filtration

The type of filter used in brewing affects each cup of coffee produced. Paper filters will provide the best tasting, clearest cup of coffee available. Bunn paper filters are excellent choices because they are porous enough to allow coffee grains to flow freely during extraction. The filters are also made from oxygen process paper that is strong enough to prevent collapsing, yet gentle enough to strain particles without taking away the flavor.

Cleanliness

To ensure cleanliness, which will affect not only your cup of coffee, but also your health, you should check the brewer and surrounding areas frequently to make sure they are free from lime and hard water deposits. The serving area around the brewer should be wiped off daily. The sprayhead or funnel, water reservoir, and
coffee decanter should be checked daily as well.

Be In the Know About Holding and Serving

Once you have brewed the perfect cup of coffee, you will want to enjoy it while the flavor and aromatic qualities are at their peak. In order to be able to relish this perfect cup of coffee, you need to know how long and at what temperature the coffee should be held at and at what temperature the coffee should be served at. The ideal temperature for holding the coffee until serving is between 175-185 degrees Fahrenheit. Even at these temperatures, a pot of coffee should not be held for more than 20 minutes in an open top container or 30 minutes in a closed top container. After this time, coffee will begin to lose its flavor.

The Science of Brewing Perfect Coffee

In order to create an impeccable cup of coffee, you need to understand the essential elements of controlling the brewing process. The basic elements of brewing are wetting, extraction, and hydrolysis.

Wetting

Coffee grounds absorb hot water from the sprayhead and then release gasses from the coffee. In order to achieve consistent extraction, the entire bed of coffee grounds must be wet during the first 10% of the brew cycle time.

Extraction

During the beginning of the brewing process, the water-soluble materials dissolve and move out of the grounds and into the water. The best flavors are extracted during the first few
minutes of the brewing process.

Hydrolysis

Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by the reaction with water. In relation to coffee, the materials created during the extraction process break down further into water soluble proteins and sugars.

Match the Grind to the Time

The brewing time or water contact time can be determined by the size of the coffee grind and bed depth. The larger the coffee grounds, the longer the brew time should be. In turn, if you are brewing more finely ground coffee, you should have a shorter water contact time. The recommended brewing contact times are shown on the chart below.

Brewer Cycle Timing

Depending on the specific brewer purchased, you can experiment with coarser or finer grind cycles to obtain the perfect cup of coffee. Each brewer will have a delivery cycle that is slightly different from the rest, so your manual can help to assist by providing recommended times for each type of coffee.

Bed Depth

Another factor in brewing an exemplary cup of coffee is the bed depth in the brewing basket. The ideal depth is 1-2 inches. If your coffee bed varies from these recommended depths, your coffee can be negatively affected, depending on whether the depth is too low or too high. If the bed is less than 1 inch, the water may move through the coffee too quickly, causing under extraction, which produces a less intense flavor and aroma. If the coffee bed is a greater depth than 2 inches, the water will flow slowly through the coffee grounds and over extract, causing an overly strong or bitter taste.

Brewing Control

The flavor of the newly brewed coffee is determined by the amount of coffee being extracted and the amount of coffee solubles. The chart below shows the relationship between all three factors, brewing ratio, strength, and extraction.

On the above chart, brewing ration is defined as the relationship between the amount of ground coffee used per half gallon of water and extraction. This is shown by the diagonal red lines. The strength/solubles concentration is the goal for percentage of coffee flavoring material as compared to the amount of water in the finished cup. This percentage is 1.15% - 1.35%, which is measured by the Brew Strength Meter, also known as the Hydrometer. At the bottom, the extraction/solubles yield is the ideal percentage of coffee material removed. This should generally be between 18% - 22% of the solubles in the coffee. The deep yellow box in the center of the chart shown the optimum balance field. This yellow box shows the perfect balance between strength and extraction that should be used in order to create the perfect cup of coffee.

What Do All of These Coffee Terms Mean?

The following terms have been used to describe the perfect cup or coffee or the brewing experience. Please refer to these definitions to more thoroughly understand the process described above.

• Soluble Materials: Compounds that dissolve in water.
• Non-soluble Materials: Compounds that do not dissolve in water.
• Volatiles: Soluble materials that evaporate easily.
• Non-volatiles: Soluble materials that do not evaporate, but stay in the solution.
• Aroma: The soluble volatile materials (gases) that evaporate, creating the coffee’s unique scent.
• Taste: The soluble, non-volatile materials (liquids) that are responsible for the flavor.
• Body: The non-soluble, non-volatile materials (solids) that determine the texture of the coffee.