What's the Purpose of Using Filter Paper in Espresso? Why Add Filter Paper to Espresso?

Some friends have noticed recently that many coffee shops are serving espresso with white paper in their coffee pucks. When he visited FrontStreet Coffee, he eagerly inquired about the true identity of this paper. Here's what it looks like↓, you can try to guess its real identity!

That's right! It's filter paper, a circular piece of filter paper. As we all know, the main purpose of filter paper is filtration - filtering out coffee grounds, even when placed in the portafilter. However, besides filtration, its addition to espresso preparation can serve other purposes, with specific effects varying depending on its placement.

In fact, FrontStreet Coffee has mentioned its function in many articles before, just without going into detail. So today, FrontStreet Coffee intends to thoroughly discuss the pros and cons of using filter paper in espresso preparation.

Adding Filter Paper at the Bottom of the Portafilter

When we talk about adding filter paper to a portafilter, it usually means adding it to the bottom. Adding a piece of filter paper at the bottom can both reduce the bitterness of the coffee and increase its cleanliness.

We know that in espresso extraction, many fine particles will be pressed out of the portafilter along with the coffee. Because these coffee particles are extremely small, they fall outside the blocking range of the portafilter filter holes. So when the coffee machine starts high-pressure extraction, these tiny coffee particles will flow out of the portafilter with the coffee and fall into the cup. Fine particles themselves carry a certain bitterness, so their presence will enhance the bitterness of the coffee while affecting its cleanliness. If we don't want an espresso to have too much bitterness and want a cleaner taste, we can place 1-2 circular filter papers flat at the bottom of the portafilter before making espresso. This way, the filter paper can act as a filter, blocking the fine particles in the portafilter. The espresso will thus have a cleaner taste and reduced bitterness.

However, it's worth noting that this approach comes with two drawbacks. With the reduction of fine particles, the coffee will lack some body. Because fine particles provide both bitterness and body. So when the fine particles in the cup decrease, the body of the coffee will also decrease. Another drawback is that it will shorten the extraction time, and the coffee's extraction rate will be relatively lower. Because the size of coffee particles is not uniform, during the extraction process, some fine particles similar in size to the bottom holes will block them, reducing the channels through which hot water can flow. This action will extend the coffee's extraction time, thereby increasing the extraction rate.

But if we add a layer of filter paper at the bottom of the portafilter, nothing will be able to block the filter holes of the portafilter. Since the hot water flow channels are restored, the flow rate during coffee extraction naturally increases. Extraction time shortens, and extraction rate decreases accordingly. FrontStreet Coffee has conducted several comparisons on the difference between adding filter paper at the bottom of the portafilter and not adding it. The results showed that espresso without filter paper had an extraction time several seconds longer than espresso with filter paper, and the extraction rate was also higher.

So if we want to reduce coffee bitterness by adding filter paper at the bottom of the portafilter, it's best to adjust the grind size with the premise of adding filter paper during extraction. Otherwise, the error between the two will make you adjust your espresso several more times, which is somewhat counterproductive.

Placing Filter Paper Above the Coffee Puck

If the filter paper is placed on top of the coffee puck, it can reduce the occurrence of channeling, allowing the coffee to achieve more even extraction.

Because there is a certain distance between the coffee puck and the shower screen, the hot water has a certain impact when it falls. Although this force won't cause hot water to directly penetrate the puck, it can easily lift the coffee particles on the surface of the puck, making channels more likely to form and extraction more uneven.

But if we add a filter paper on top of the puck, it can disperse the impact of water before it contacts the puck, while allowing water to spread more evenly and pass through the coffee bed, thereby achieving more even extraction. But if you ask about the actual improvement it brings to extraction... it's relatively not that significant. Because channeling is more often caused by operational issues such as improper tamping or too many clumped coffee particles. That's why few people add filter paper to the surface of the puck; most do it at the bottom of the portafilter.

Adding filter paper on top of the puck will result in extended extraction time, because hot water needs to pass through more material, so extraction time naturally extends. The specific extension time depends on the thickness of the filter paper - the thinner the filter paper, the less the extraction time is extended; the thicker the filter paper, the more the extraction time is extended. This is not necessarily a bad thing, because it means we can use less coffee or coarser grind for extraction. We are no longer limited by the standard of the portafilter, and the use of coffee amount can be more flexible.

Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473