How Water Quality Affects Coffee Extraction: One of the Key Factors

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01 | Introduction

We know that the main factors affecting coffee include origin, roasting, grinding, water temperature, ratio, brewing method, freshness, and water quality. Regardless of the factor, all are studied from a scientific perspective to understand how various changes affect coffee flavor, all returning to the essence. Our research method generally uses single-variable control to understand the impact of certain factors.

How does water quality affect coffee? The reasons for focusing on water quality to study coffee extraction in this article are as follows:

A cup of coffee is about 99% water, and only 1% coffee components can cause huge changes in the entire cup. Most people think water only serves as a carrier and has minimal impact on coffee flavor.

Researching the impact of water quality is more difficult compared to other factors. Water that appears identical cannot be distinguished by the naked eye in terms of its internal composition differences.

The main reason for writing about water quality is that most people don't重视 water's impact.

02 | Understanding Water

Believe most people have had the experience of tasting sweetness in water. So the question arises: why does purified water taste slightly sweet?

Here is what I believe to be a more convincing explanation:

In fact, water processed through a pure water machine (with built-in reverse osmosis membrane) should not have any particular taste - accurately speaking, it should be tasteless. Many people feel that processed water has a "sweet" taste, but actually, this should be because the water they drank before contained too many impurities, had flavors or off-flavors, and over time, this affected the taste buds' accurate judgment of water's taste.

In this situation, when the drinking water suddenly becomes much cleaner, this significant contrast is the fundamental reason that makes you feel the water has a sweet taste - it's as simple as that.

Before understanding water, we need to understand the factors that affect water quality: TDS, hardness (GH), and pH value.

Hardness (GH)

Soft water: Water that contains no or only small amounts of soluble calcium and magnesium compounds is called soft water.

Hard water: Hard water refers to water containing relatively high amounts of soluble calcium and magnesium compounds.

TDS

Also known as Total Dissolved Solids, the higher the TDS value, the more dissolved substances the water contains, including both inorganic and organic content. The measurement unit is: milligrams per liter (mg/L).

PPM is a concentration unit meaning parts per million. It refers to the number of milliliters of solute contained in one million milliliters of solution, or indicates the number of grams of solute contained in one million grams of solution.

Conversion relationship: 1 mg/L = 1 PPM

pH Value

Also called hydrogen ion concentration index: it's a measure of hydrogen ion activity in solution, which is the standard measure of the acidity or alkalinity of a solution in the usual sense.

03 | How Water Affects Coffee Extraction

According to coffee extraction theory, we know that:

When the TDS value is too high, the minerals in the water are oversaturated, and there isn't enough space to extract the flavors from the coffee (mentioned in "Water for Coffee");

When the TDS value is too low, the water's penetration capability might be insufficient, causing under-extraction.

I previously thought that the lower the TDS, the theoretically easier the extraction. Why does the reality easily cause under-extraction?

The key point is: some compounds in hard water are "sticky" - during the coffee making process, they tightly hold onto compounds in the coffee. Calcium and magnesium are particularly sticky. If water contains large amounts of magnesium ions, the coffee will have a stronger taste and higher caffeine content. However, hard water also contains more carbonates, which Hendon found may be the source of more bitterness in coffee. Soft water often has a lot of sodium, but it's not sticky (neither helpful for extracting good or bad components from coffee).

SCA research shows that water with a PPM value between 125-175 is most ideal for coffee extraction. PPM values below 75 more easily lead to over-extraction; PPM values above 225 more easily lead to under-extraction.

Conclusion: The impact of TDS on coffee extraction is relative, depending on the proportion of components in your water that are beneficial for extracting good coffee components. (For example, a low TDS value with high calcium and magnesium ion content is beneficial for coffee extraction).

04 | Experimental Verification

Experimental Equipment:

A certain brand of distilled water, a certain slightly sweet mountain spring water, Clever Dripper, TDS testing pen.

Selection Reasons:

Distilled water is the most extreme soft water, containing no substances, making it more comparative; the slightly sweet mountain spring water has a low TDS value but relatively high calcium and magnesium content,符合 the theoretical basis for beneficial coffee extraction; the Clever Dripper's immersion extraction can reduce experimental errors caused by brewing techniques.

TDS Testing:

Distilled Water:

Certain Slightly Sweet Mountain Spring Water:

Slightly Sweet Soluble Substance Data:

Brewing Data:

Test Coffee Beans: Natural 90+ Zhumaang (roasted on May 19)

Brewing Method: Pour-over

Grind Size: 4W (BG)

Clever Dripper, 18g coffee grounds, water temperature 90°C, water-to-coffee ratio close to 1:16

45g water for bloom, bloom time 20s

Then add water to 288ml, total time 3 minutes.

Test Group 1 (Distilled Water):

Flavor Description: Wet aroma is floral with faint berry fragrance. Obvious citrus acidity and sweetness upon entry, clean mouthfeel, moderate body, flavors concentrated in front-middle section, faint sweet aftertaste, no obvious characteristics of natural processed beans, more like washed beans.

Sweetness: ☆☆

Acidity: ☆☆☆☆

Bitterness: ☆

Body: ☆☆

Test Group 2 (Mountain Spring Water):

Flavor Description: Relatively weaker acidity, cane sugar sweetness and honey sweetness upon entry, thick and weighty mouthfeel, clean with long aftertaste, overall comfortable and pleasant feeling.

Sweetness: ☆☆☆☆

Acidity: ☆☆

Bitterness: ☆

Body: ☆☆☆☆

Comparison Conclusion:

The coffee brewed with mountain spring water has lower acidity than distilled water but much higher sweetness, with nearly perfect body performance including aftertaste.

The coffee brewed with distilled water didn't show the under-extraction I expected - it seemed to have extracted the front-middle section, showing strong acidity, upper-medium sweetness, and a clean, bright flavor with its own charm. The relatively weaker acidity in mountain spring water coffee is due to its excellent sweetness covering its existing acidity. However, the mountain spring water coffee is thick and weighty with high sweetness, indicating that mountain spring water has a higher extraction rate than distilled water. This also proves the conclusion that relatively low TDS with sticky dissolved substances is more beneficial for coffee extraction.

05 | Conclusion

Regarding the impact of water quality on coffee, the conclusions in this article may only apply under certain conditions and may be one-sided. But the joy of coffee lies here - we verify our doubts, continuously learn, and continuously understand.

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