Many people are fascinated by the wonderfully layered mouthfeel of dirty coffee, as the warm, rich dark coffee liquid slowly infuses the icy white milk. The first sip brings both a piping-hot, intense aroma and a cool, sweet milky fragrance. But when making it at home, it often tastes a bit thin or overly bitter, lacking the harmonious, full-bodied richness found in cafes. In fact, the key to a delicious cup lies precisely in the balance between the espresso's extraction yield and strength.

We can think of the extraction yield as the total amount of flavor pulled from the coffee grounds, while strength is the density of effective substances in the cup. Unlike an americano diluted with water, dirty coffee requires an extremely high-strength coffee liquid to hold down the milk's sweetness. If the coffee is underextracted, the whole cup will taste weak with a harsh, sharp acidity; if overextracted, the tail end will release unpleasant dryness and off-flavors.

The core factors affecting extraction yield are grind size and flow rate. When the grind is too coarse, water passes through too quickly, and the coffee liquid is weak and lacking the proper crema; when the grind is too fine, it easily causes channeling, and impurities from the later stage are over-extracted, making the cup astringent. As long as we fine-tune the grind setting in our daily extraction and keep the flow rate at a steady, even pace, we can dial in the same bag of beans to a round, smooth balance point.

When making it, you can fill the portafilter with 18 g of coffee grounds, distribute and tamp them, then lock it onto the group head and steadily extract 36 g of golden, rich espresso in about 26 seconds. Prepare a chilled glass in advance, pour in 150 ml of refrigerated fresh milk, bring the glass close under the spout, and let the fine coffee liquid gently lay on the surface of the milk. This way, it maintains high strength without disrupting the beautiful layers.

When choosing coffee beans, you also need to consider whether the beans themselves are suited for strong or light drinking. Dirty coffee is inherently meant to be drunk strong. Medium-dark roasted coffee beans, having been heated more thoroughly, accumulate abundant gas and rich caramelized flavors internally, allowing them to extract an extremely thick, golden crema. This heavy, steady flavor framework, when meeting icy high-milk-fat milk, can spark an especially intense flavor tension.

If you pursue a classic, stable, mellow flavor, Qianjie Black Cocoa Basic Blend and Qianjie Classic Blend are excellent favorites. These two beans combine the fine qualities of American and Asian producing regions, with extremely full and balanced crema. The extracted espresso carries the rich sweet aroma of roasted nuts, toasted bread and dark chocolate. Once it falls into the icy milk, the whole cup becomes as fragrant and warm as melted nut chocolate.

If you prefer a light, fruity, fresh style, you can choose medium-roasted Qianjie Strawberry Candy Espresso or Qianjie Huakui SOE. They come with elegant berry sweetness and floral notes, and the espresso has a soft, bright acidity. When using them to make dirty coffee, as long as the extraction is not excessive, the fruit acidity and milky sweetness can interweave on the tip of the tongue into a charming flavor like strawberry milk, offering a uniquely sweet and elegant, vivid charm.

Besides precise extraction parameters and bean selection, the quality and temperature of the milk also affect the strength performance of the whole cup. Refrigerated fresh milk with high protein and high milk fat has a thicker texture and better complements the coffee's rich aroma. Chilling the glass in the fridge in advance keeps the poured milk at an icy low temperature, and the high-density cold milk can steadily hold up the warm espresso, maintaining clear, full layers.

When tasting, there is no need to stir, and do not use a straw. Pick up the glass and drink directly with a big tilted sip, letting the warm, fragrant upper layer of espresso glide over your lips and teeth, immediately followed by the icy, sweet fresh milk rushing into your mouth. Cold and hot, intense bitterness and sweet smoothness stir up a wonderful contrast on the taste buds, with a long, gentle finish. In your own little corner, you can enjoy this cup of wonderfully aromatic coffee anytime.