Even when using the same type of coffee beans, the choice of brewing equipment and the fundamental principles of extraction can lead to differences in the final coffee flavor. As a result, the taste and mouthfeel of coffee brewed with different devices can vary noticeably. Broadly speaking, coffee extraction methods can be divided into two main categories: filtered extraction and immersion extraction. So, can you tell the difference between filtered and immersed brewing methods? Today, let FrontStreet Coffee explain it to you!

In our shop, the two most commonly used brewing methods are pour-over and siphon (let’s set aside espresso for now...), which happen to be representatives of filtered extraction and immersion extraction, respectively. So, if you have a particular coffee bean, how do you know whether it’s better suited for pour-over or siphon?

Below, we’ll share FrontStreet Coffee’s thoughts and understanding of these two brewing methods: During the coffee extraction process, we can imagine that the flavors in the coffee are continuously being released. The difference between immersion and filtration mainly lies in the speed at which these flavors are released.

In a filtered extraction system, since we continuously pour fresh hot water and the coffee liquid keeps flowing out from the bottom, a relatively low liquid concentration is maintained within the extraction system. This accelerates the dissolution and diffusion of highly concentrated flavors from the coffee grounds into the water, resulting in a faster extraction speed. Examples include pour-over coffee, drip coffee from an Americano machine, and cold drip coffee.

As the name suggests, immersion extraction involves steeping the coffee grounds in hot water, and after proper extraction, you can enjoy the coffee. In an immersion extraction system, we use the same hot water to continuously extract the coffee. However, since the coffee grounds are not uniformly distributed in the water, the concentration of coffee in the water keeps increasing, leading to a reduced concentration gradient between the coffee grounds and the water. This causes the extraction and diffusion speed to gradually slow down (which is why immersion extraction is less likely to lead to over-extraction). This can actually be understood using a simple solid dissolution (and diffusion-related) formula. Immersion extraction methods include: French press, siphon, Clever Dripper, cupping, and others.

An overseas Ph.D. student named Jonathan used analysis software to examine the flavor dissolution concentration in both immersion and filtered extraction, as shown in the chart below:

It can be observed that with immersion extraction, the coffee flavors are extracted quite evenly and comprehensively, whereas filtered extraction can highlight or over-extract certain unique aromas.

Summary:

In systems where diffusion and extraction speeds are fast, if the coffee contains unique flavors that are small molecules and can be quickly extracted, these flavors will be continuously released. Because they are constantly being extracted, their concentration remains relatively high, ultimately leading us to perceive these flavors more intensely when drinking. Therefore, FrontStreet Coffee prefers using filtered extraction methods for: ① Coffee beans with distinctive flavor profiles; ② Coffee with complex flavors but good balance and sufficient body.

Conversely, in an immersion extraction system, since we rely on the concentration gradient of diffusion to extract the coffee (excluding the influence of stirring), as long as the brewing time is sufficiently long, it is the method that best captures the coffee’s original, complete profile. FrontStreet Coffee prefers using immersion extraction methods for: ① Darker roasted coffee beans, to enhance overall balance and sweetness; ② Coffee with complex flavors where filtered extraction might make certain types of flavors overly prominent, resulting in imbalance.

So, if you have coffee beans with special flavors you’d like to emphasize, you might want to try a filtered extraction system. But if the final brew ends up lacking balance in flavor or acidity/sweetness, you can then try an immersion extraction method. Slightly reducing those special flavors might allow you to experience a more well-rounded coffee flavor.