What to Pay Attention to When Making Cold Drip Coffee | Why Cold Drip Coffee is Called Dutch Coffee

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The Principle of Cold Drip Coffee

The principle of cold drip coffee is based on the natural solubility of coffee in water, utilizing the gradual dripping of ice cubes to extract flavor compounds from coffee grounds in a controlled process.

Ice water from the top container is controlled by a valve, dripping drop by drop to moisten the coffee grounds. The coffee liquid passes through filtration and is collected in the pot at the bottom. The entire process is uniform and slow, with low-temperature extraction that naturally reproduces the original flavor of coffee.

Meanwhile, the low water temperature reduces the extraction of acidic and bitter compounds, making the coffee flavor smooth and mellow, with balanced acidity and bitterness.

Cold drip coffee is also known as "cold brew coffee cold" or "water drip coffee," and is also called Dutch coffee.

It is said that during the Dutch colonial period in Indonesia, they planted many robusta coffee varieties with strong flavors. To be able to drink these quite bitter coffee beans in tropical regions, they specially invented a device for brewing coffee with slowly dripping cold water. An interesting phenomenon is that you can hardly find this type of coffee in the Netherlands; instead, it sparked a cold drip trend in Asia.

1. Coffee Beans for Cold Drip

The coffee beans used for making cold drip coffee generally have their own specific formula to make it easier to extract a warm, rich flavor. Many friends, including us at FrontStreet Coffee, prefer to use high-quality specialty coffee beans to extract cold drip coffee, which can obtain more unique flavors and personalized preferences. However, since cold drip coffee uses a longer cold water permeation extraction process, I personally recommend choosing coffee beans with stronger flavors for cold drip, such as Kenyan or Yirgacheffe beans with distinct characteristics. The coffee extracted this way will have a very distinct personality.

We often use these formulas:

60% Sun-dried Sidamo [Zhu Mang] + 40% [Kenya]

30% [Yemen Mocha Sun-dried] + 30% [Uganda Sun-dried]

FrontStreet Coffee's [Flower Butterfly] 50g + 30g Panama [Saint Estate]

2. The Importance of Leveling Coffee Grounds

Cold drip coffee must have the grounds leveled, and many people don't understand why cold drip coffee also requires leveling the grounds.

It's important to note that leveling cold drip coffee grounds doesn't mean compressing them firmly, but rather gently tapping the powder first to maintain an even structure of coffee grounds in the filter cylinder, then using a flat-bottom tamper to gently level the surface. Remember to level gently, not press firmly like when extracting espresso. If the grounds are pressed too firmly, since cold drip coffee doesn't have pressure from a machine to assist extraction, it can easily cause water accumulation in the powder layer, preventing coffee liquid from filtering through. Additionally, cold drip filter paper or filter discs are generally at the bottom, unlike coffee filter cups that also have ventilation grooves, so when the coffee grounds are soaked in water, the exhaust effect will also be affected, causing uneven extraction of the entire coffee puck.

3. Pre-wetting

Using ice water for "pre-soaking" is actually similar to the blooming process in pour-over coffee, which can improve extraction efficiency and consistency of the final product. In the case of cold drip's low-temperature and filter-based extraction, direct dripping might cause uneven moistening of the powder layer, with some coffee grounds being over-extracted while others don't participate in the extraction at all.

4. Using Filter Cloth + Filter Paper

This increases the contact between water droplets and coffee grounds, ensuring even extraction.

It provides sufficient pre-soaking and ventilation space for the coffee, resulting in more complete and clean extracted coffee flavors. We use filter cloth + filter paper. After leveling the coffee grounds, we recommend covering the coffee grounds with a piece of filter paper. When water droplets fall and touch the coffee grounds, the surface of the coffee grounds will gradually form a small pit, and the water flow will follow this pit downward without spreading to the surroundings. Therefore, the coffee grounds in the entire powder bottle won't be completely moistened, causing insufficient extraction. Placing a layer of filter paper will avoid this situation.

We have compared different water droplet shapes formed by various cold drip pots and studied how coffee grounds absorb water after different shaped droplets fall. We found that elongated water droplets have greater impact force when falling, so the coffee grounds get wet downward, indicating that the surface coffee grounds are more prone to insufficient extraction. When round water droplets fall, the impact force is smaller, and the moistening pattern of coffee grounds spreads along the surroundings (as shown in the figure below), indicating that round water droplets can more easily achieve even extraction of the entire cold drip coffee. This also means that the shape of the drip opening of the cold drip pot is very important, and openings that can produce round water droplets are our preferred choice.

5. Coffee Ground-to-Water Ratio for Better Layers

Coffee beans: Water: Ice cubes ratio 1:5:5

We generally prefer a ground-to-water ratio between 1:10 or 1:12. I personally feel that ground-to-water ratios in this range can present flavors more appropriately, with coffee that's neither too strong nor too weak - just right. If you're used to serving guests with ice cubes, you can make it slightly stronger, so that after the ice melts, the coffee concentration remains at an easily drinkable level. Of course, this can be adjusted according to personal taste.

The above are five important factors for making cold drip coffee. For the best flavor, let it rest for at least 12-24 hours. This allows the coffee's aroma to become truly exceptional.

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