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

01 | Introduction

The main factors affecting coffee include origin, roasting, grinding, water temperature, ratio, brewing method, freshness and water quality. Each is studied from a scientific perspective to understand how various changes affect flavor, always returning to the essence. Our research method generally uses single-variable control to isolate the impact of a given factor.

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

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

Researching the impact of water quality is harder than other factors. Water that looks identical cannot be distinguished by the naked eye in terms of its internal composition.

The main reason for writing about water quality is that most people do not value water's impact.

02 | Understanding Water

Most people have tasted sweetness in water. So why does purified water taste slightly sweet?

Here is what I believe is a more convincing explanation:

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

In that situation, when the drinking water suddenly becomes much cleaner, the significant contrast is the fundamental reason you feel the water has a sweet taste. It is 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, both inorganic and organic. 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 the number of grams of solute contained in one million grams of solution.

Conversion relationship: 1 mg/L = 1 PPM

pH Value

Also called the hydrogen ion concentration index. It is a measure of hydrogen ion activity in solution, 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 is not enough space to extract the flavors from the coffee, as noted 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 low TDS in reality easily cause under-extraction?

The key point is that some compounds in hard water are "sticky." During brewing, 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. 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 sodium is not sticky, neither helping nor hurting the extraction of good or bad components.

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, a Clever Dripper, a TDS testing pen.

Selection Reasons:

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

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: The wet aroma is floral with a faint berry fragrance. Obvious citrus acidity and sweetness on entry, a clean mouthfeel, moderate body, flavors concentrated in the front and middle, a faint sweet aftertaste, and no obvious characteristics of natural processed beans, more like washed beans.

Sweetness: 2/5

Acidity: 4/5

Bitterness: 1/5

Body: 2/5

Test Group 2 (Mountain Spring Water):

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

Sweetness: 4/5

Acidity: 2/5

Bitterness: 1/5

Body: 4/5

Comparison Conclusion:

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

The coffee brewed with distilled water did not show the under-extraction I expected. It seemed to have extracted the front and middle sections, showing strong acidity, upper-medium sweetness and a clean, bright flavor with its own charm. The relatively weaker acidity in the mountain spring water coffee comes from its excellent sweetness covering the acidity that is there. 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 supports 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 exactly here: we verify our doubts, keep learning and keep understanding.

FrontStreet Coffee Recommendation

Water matters most with coffees that have something to reveal, and a medium roast is a smart place to start, because roasting is a balance of acidity, sweetness and bitterness. The darker the roast, the more bitter and heavy the cup; the lighter the roast, the more acidic and light it is. Medium-roasted beans sit in the middle, which is why they respond clearly to changes in water and taste balanced overall.

FrontStreet Queen Estate is a good example. Grown in Brazil, the world's largest coffee producer, from the distinctive Yellow Bourbon variety, it is quietly sweet and gentle, and after a medium roast shows creamy peanut, chocolate, toasted bread and sugarcane aroma and sweetness. It works as a pour-over and also in a moka pot or an espresso machine. FrontStreet Strawberry Candy Geisha Blend is the sweeter option: it combines two well-known Central and South American origins, a honey-processed coffee from Costa Rica and a washed Geisha from Panama, and a medium roast brings out both orange-blossom honey character and a round sweetness, suiting cold brew, pour-over and espresso alike.

For a reliable everyday cup, FrontStreet 2013 Sun-Dried Typica represents Chinese specialty coffee with the orthodox Yunnan Small Bean profile. A medium roast keeps its balanced, gentle character, with soft notes of nut, brown sugar, red tea and dried apricot, useful for pour-over, cold brew or a drip machine at very good value. And FrontStreet Jamaica Blue Mountain No. 1, grown from the Typica variety, is famous for its balance: a medium roast fuses its acidity, bitterness, sweetness and body into an elegant whole, with chocolate, roasted nut, cream and caramel on the first sip.