What is the Impact of Water Quality on Coffee Extraction: A Brief Analysis of How Hot Water Amount Affects Coffee Extraction

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FrontStreet Coffee - The Impact of Water Temperature and Volume on Coffee Extraction

Water quality includes factors such as total hardness, alkaline hardness, pH value, and water source. Generally, "water quality" in coffee extraction refers to "total hardness." This article will explain related terms with the simplest possible statements and summarize a minimalist yet scientific logical method to understand the impact of water hardness on coffee.

1. Extraction ≠ Dissolution

The essence of extraction refers to ions from substance A displacing B's ions from substance B and entering A. The term "extraction" commonly used in coffee circles for a long time only referred to physical "dissolution" without considering the chemical concept of "extraction." That is, only saturation was considered.

2. Saturation

This refers to the maximum value of water-soluble substances dissolving in water at a specific temperature, generally measured by weight.

The saturation of any water-soluble substance is not constant and changes with temperature and pressure variations, such as in espresso.

Assuming the same bean is perfectly extracted in both espresso and pour-over brewing methods, the extremely high concentration of espresso depends on its much higher saturation of various water-soluble substances compared to pour-over, due to the high pressure in the portafilter. When espresso liquid enters a cup at normal pressure, some supersaturated substances will precipitate and crystallize, while others won't have time to crystallize, thus creating different tactile sensations from pour-over, such as thickness, graininess, silkiness, or other distinct textural feelings.

3. Total Water Hardness

This refers to the total concentration of calcium, magnesium, carbonates, chlorides, and other salts in water. After heating, carbonate substances decompose and precipitate, and are no longer counted in total hardness.

The common unit of water hardness measurement in coffee circles is the same as in the United States, namely ppm, which means 1 ppm when 1 milligram of calcium carbonate is contained in 1 liter of water.

Generally, the hardness of water used for coffee is between 100-140ppm. Slightly higher or lower values are also acceptable, depending on the coffee itself and brewing methods, with no standard hardness value.

4. Extraction Capacity of Total Hardness

Theoretically, the higher the water hardness, the stronger the extraction capacity, making it easier to extract coffee—not more difficult. Why?

Firstly, here we only discuss hardness, that is, calcium ions, magnesium ions, chlorides, etc., in the water, not "saturation."

Secondly, the chemical property of extraction is "displacement." The higher the water hardness, the more various ions it contains, the stronger the displacement capacity, thus the stronger the extraction capacity, making it easier to extract coffee. For example, under the same conditions, using 100ppm water to extract coffee results in a higher extraction rate than using 0ppm water.

If the water temperature for extracting coffee is too high, it will extract more flavor substances prematurely, ultimately leading to excessive extraction substances in the coffee. The amount of water used for extraction will also affect the overall flavor and potentially make the coffee taste thin.

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