Aroma + Taste = Flavor

Some of the chemical compounds in coffee evaporate easily and are responsible for the brew’s aroma. Others aren’t so volatile and are the source of the brew’s taste. The combination of aroma plus taste constitutes coffee’s flavor. Further, there are the insoluble compounds – the ones that don’t break down from contact with hot water – those become coffee’s body.

Three Phases of the Brewing Process

Phase One: Wetting

As the coffee fibers absorb hot water, gas is driven from the coffee and the small spaces inside the particles. This phase prepares the particles for the extraction of solubles.

Phase Two: Extraction

During this phase the water-soluble flavoring compounds dissolve and rapidly move from the coffee fibers and into the water.

Phase Three: Hydrolysis

During this phase, large molecules of water-insoluble carbohydrates break down into smaller molecules that are indeed water-soluble. These are mostly reducing sugars.

Variables of Coffee Brewing

In total, 24 variables interact throughout the brew process. Understanding of these variables and the ability to control them is a critical element to the coffee craft. They are categorized as follows:

Blend Components

1. Ratio of different coffees – from single-origin to a mix of Arabica and Robusta.

2. Bulk density – the beans’ weight in relation to their physical volume.

3. Chemical composition – which varies by the type of coffee plant and micro-climate in which it grows.

Roast Development

4. Methodology of roasting – mostly a consideration of the efficiency of heat transfer with the beans, which determines uniformity from the outside to the center of each bean.

5. Rate of roasting – controls the structural expansion of the bean fibers (affecting extraction rate) and the chemical composition of the roasted bean (affecting flavor of the extract).

6. Degree of roast – evaluated by the beans’ color.

7. Rate of degassing – relates to the method of storage or the length of time between roast and brewing.

Grind

8. Average size – the average size of the coffee particle.

9. Size distribution – the range of sizes of coffee particles, as well the amount of various sizes.

10. Particle shape – which can be affected by the type of grinder and burrs used.

Time of Brew

11. Contact time – how long the coffee remains in contact with the water, which determines soluble yield

12. Contact temperature – must be near 200 degrees Fahrenheit (195-205).

13. Temperature gradient – throughout the brew cycle the water must be maintained between 195 to 205 degrees Fahrenheit.

Turbulence

14. Complete wetting – ensuring that all coffee grounds have been saturated.

15. Uniform flow rate – the velocity of the water flow.

16. Particle movement – affected by the bed’s size, depth, configuration and containment.

Filtering Method

17. Method of separation – determined by the filter type selected.

18. Degree of clarification – the extent to which non-soluble materials are removed as the brew passes into the holding container.

Holding Conditions

19. Length of time and method of holding – coffee should be served immediately or kept in a thermal container.

20. Holding temperature – should be maintained at 175 to 185 degrees Fahrenheit throughout holding.

Brewing Formula

21. Coffee by weight – too much coffee can lead to under-developed flavor.

22. Water by volume – too much water can lead to over-extracted and often bitter flavor.

Water

23. Water composition – the amount of dissolved minerals,which may prohibit proper extraction.

24. Water treatment – improves the flavor of coffee by removing unwanted chemicals from water, such as chlorine.

Controlling the Variables

To master the craft of coffee brewing, the many variables that contribute to both the strength (intensity) and extraction (acceptability) to coffee flavor must be controlled. The skill lies in learning how to control all of the variables so that the solubles concentration is balanced with the solubles yield, resulting in the perfect cup of coffee that exceeds consumers’ expectations.

Although that possible combinations of 24 variables are virtually limitless, one can provide reasonable control over the process by adhering to the key principles of good brewing: quality coffee, excellent equipment, clean water and the proper brewing ratio.