How does coffee extraction differ between percolation and immersion?

Coffee extraction follows two main paths: percolation and immersion. In percolation, fresh water keeps flowing in while brewed coffee drains away, so the concentration gradient stays large and flavor compounds move into the water quickly. In immersion, the grounds sit still in hot water, the gradient narrows, and diffusion slows, giving a more balanced cup.

The practical choice follows the beans. Pour-over, a percolation method, tends to amplify a bean's distinctive aromas and bright notes, while siphon, an immersion method, presents its original character in a fuller, more even way. When reading a recipe for an american drip coffee maker, the same principle applies: continuous flow favors clarity, steeping favors balance.

The same coffee bean can taste completely different in the cup when brewed with a different extraction device. Coffee extraction paths can be broadly classified into two types: percolation and immersion. The most fundamental difference between them lies in the speed at which flavor compounds diffuse into the water. In percolation, because fresh water is continuously poured in and brewed coffee is drained away, the concentration gradient is large and extraction is fast, which tends to amplify the bean's distinctive aromas. In immersion, the coffee grounds sit still in hot water, the concentration gradient gradually narrows, and diffusion slows down, allowing the coffee's original character to be presented in a more balanced and complete way. Starting from the underlying principles and combining an analysis of flavor dissolution concentration, this article will help you judge whether the beans in your hands are better suited to pour-over or siphon, and offer specific selection advice.

Even with the same coffee bean, once you switch to a different extraction device, the final flavor direction of the brew will change due to differences in extraction principles. For this reason, coffee made with different brewing methods often shows noticeable differences in taste experience. Coffee extraction paths can be broadly divided into two types: percolation extraction and immersion extraction. So, can you accurately distinguish between these two brewing methods? Next, let the editor walk you through them.

In daily cafe service, the two most commonly used brewing methods are pour-over and siphon (espresso is temporarily excluded from discussion...), and they happen to correspond respectively to percolation extraction and immersion extraction. So here comes the question: if you have a bag of beans on hand, how do you determine whether it is better suited to pour-over or siphon?

Below, let me share with you the editor's understanding and experience of these two brewing methods: throughout the extraction process, it helps to imagine the release of coffee flavor as an ongoing process, and the core difference between immersion and percolation lies in the rate of flavor release.

In a percolation extraction system, hot water is continuously replenished and poured in, while brewed coffee also continuously drains from below, so the liquid concentration in the entire extraction system is always maintained at a relatively low level. This accelerates the dissolution and diffusion of high-concentration flavor compounds from the coffee grounds into the water, making the overall extraction speed relatively fast. Common methods include pour-over coffee, American drip machines, cold brew coffee, and so on.

Immersion extraction can be understood literally—coffee grounds are immersed in hot water, and once extraction reaches the appropriate level, it is ready to drink. In an immersion system, the same batch of hot water is used throughout. Extraction continues all along, but because the coffee grounds are not evenly suspended in the water, the coffee concentration in the water keeps rising. The concentration gradient between the coffee grounds and the water narrows accordingly, and the diffusion speed gradually slows down (this is also why immersion extraction is relatively less prone to over-extraction). This can actually be understood with the help of a simple solid dissolution formula (related to diffusion). Methods belonging to immersion extraction include: French press, siphon, smart cup, cupping, and so on.

A doctoral student abroad named Jonathan once used analysis software to analyze the dissolution concentration of coffee flavor under immersion extraction and percolation extraction. The results are shown in the figure below:

As can be seen from the figure, with immersion extraction, the coffee flavor is extracted quite evenly and completely; while percolation extraction tends to highlight certain special aromas, and may even over-extract them.

Summary:

In a system with fast diffusion and extraction speed, if a certain type of flavor in the coffee consists of small molecules that can be extracted quickly, then it will be released continuously. Because it is continuously extracted, its concentration will naturally be relatively high, and ultimately this flavor will be perceived especially strongly when drinking. Therefore, the editor prefers to use percolation extraction to brew: ① coffee beans with distinctive flavor characteristics; ② coffees with complex flavors but sufficiently high balance and body.

Conversely, in an immersion extraction system, because extraction relies on the diffusion concentration gradient (ignoring the influence of stirring for now), as long as the time is long enough, this is a brewing method that best restores the complete appearance of the coffee. The editor prefers to use immersion extraction to brew: ① relatively dark-roasted coffee beans, to improve overall balance and sweetness; ② coffee beans with complex flavors that, when brewed with percolation extraction, have certain flavors that are too prominent and cause imbalance.

So, if a certain coffee bean has a special flavor you want to emphasize, you might try a percolation extraction system; but if the final brewed coffee is not ideal in flavor and sweet-acidity balance, then you can switch to immersion extraction and give it a try. Perhaps after slightly weakening some of the distinctive flavors, you may instead taste a more complete expression of this bean.

That is all for this sharing session. I hope this content is helpful to everyone. Which brewing system do you prefer?

The above content is compiled by CoffeeHunters, a coffee news website.