When making a refreshing, thirst-quenching iced coffee, most people focus their attention on the bean's origin and roast level, but in fact more than 98 percent of the cup is water. At low temperatures, the tongue's perception of aroma becomes slower, and the mineral content and hardness of the water are precisely the key that determines whether the aromatic compounds in the coffee grounds can dissolve smoothly and whether the sweet-tart balance can unfold.

Water's dissolving ability is mainly affected by total dissolved solids, commonly known as TDS. Distilled or purified water has very few minerals, with TDS usually below 10; when used to extract a light-roasted iced coffee, water molecules can more purely capture floral notes and fruit acidity, giving a light, translucent mouthfeel. But if used to brew beans that are themselves low in sweetness, the finish often comes across as thin and dry.

Bottled natural water or soft water containing a moderate amount of calcium and magnesium ions, with TDS maintained between 40 and 90, works differently: magnesium ions help adsorb lively fruit aromas, while calcium ions set off a creamy, rounded texture. This kind of water is more forgiving of a bean's flavors; made into an iced drink, it preserves clear layers while keeping the fruit acidity from tasting thin, making it especially suitable for iced pour-over or cold brew.

If you want a cup of iced coffee overflowing with floral aroma and as clear as iced lemon black tea, Qianjie Yirgacheffe Gedingding is an especially fitting partner. This light-roasted natural bean carries citrus, berries and a delicate tea note; brewing with low-mineral water lets its light floral-fruity tone unfold completely. For pour-over, take 15g of grounds, pour 91°C hot water at a 1:15 coffee-to-water ratio, first bloom with 30ml of water for 30 seconds, then gently pour in three stages up to 225ml, keeping the total time to 2 minutes 05 seconds; the brewed coffee falls directly into a cup filled with pure-water ice cubes, giving a soft, sweet aftertaste.

If you prefer a richer tropical-fruit sweetness, Qianjie Ethiopia Huakui displays abundant passion fruit and ripe strawberry aromas. The natural process gives it a full, fermented fruit sweetness; this style is not only good for iced pour-over but also well suited to slow-steeped cold brew. Here, choosing weakly mineralized water with a TDS of around 50 can more steadily bring out the sweetness of ripe berries in a low-temperature environment, making the acidity soft and lingering.

If your everyday drinking water at home is high in minerals, or your filtered tap water tastes hard, the bicarbonate in the water will neutralize part of the coffee's lighter organic acids. In that case, forcing the use of an extremely light-roasted floral bean tends to make the iced coffee flat and dull. Faced with harder water, a smarter approach to choosing beans is to pick African high-altitude varieties with abundant acidity and a strong juicy feel.

Qianjie Kenya Little Tomato is exactly the ideal choice for dealing with higher-mineral water. It inherently has intense cherry tomato, smoked plum and yellow sugar notes, and its acidity framework is very firm; even when it meets medium-hard water, it will not be completely masked, but instead transforms into a full, juicy, substantial mouthfeel. When making iced coffee, use 15g of grounds, a 1:15 coffee-to-water ratio and 89°C water; after a 30-second bloom, pour steadily in two stages up to 225ml, with a total time of 1 minute 55 seconds. Once cooled, it presents a sweet-tart layering like a smoked plum tomato drink.

In the system of diluting iced espresso with water to make an iced americano, water quality has an equally notable effect on crema emulsification and flavor extension. When making it, use 18g of coffee grounds, adopt low-pressure pre-infusion followed by constant-pressure extraction, and extract 36g of espresso within 26 seconds. Pour this espresso, with its fine crema, into softened purified water filled with ice cubes; it instantly locks in the coffee's refreshing nutty aroma and brisk acidity, and the whole iced americano is clean and easy to drink.

When choosing beans suitable for iced coffee, it is worth first taking a look at what kind of water is in your kettle. Crisp, low-mineral water is suited to lifting delicate floral-fruity aromas; water rich in moderate minerals can outline a fuller sweetness more gently; and beans with firm acidity can stay vivid under all kinds of water. Once you sort out the interaction between water and beans, every cup of iced coffee in summer can unfold its own abundant flavors.