What Are the Different Uses of Filter Paper? Does Cold Brew Coffee Need Filtering? Can You Use Filter Paper with a Moka Pot? How to Filter Coffee Grounds?

Yesterday, FrontStreet Coffee shared that the difference between various coffee filters is as vast as the difference between humans and chimpanzees. Since the topic was filters, many friends in the comments section asked other questions about filters. For example: "Besides pour-over coffee, what else can filters be used for?" and "Can moka pots use filters?" (Excellent! This successfully helped FrontStreet Coffee find today's topic!)

Although pour-over coffee is the primary use for filters, other extraction methods also have varying degrees of filter usage requirements. Moreover, filters serve different functions in different applications (though their essence remains filtration). Today, FrontStreet Coffee will share what other coffee extraction methods use filters besides pour-over coffee and what the differences are.

Cold Brew Coffee

When discussing filter applications beyond pour-over, we must first mention cold brew coffee, as cold brew's filter usage needs are quite significant. As everyone knows, cold brew is made by mixing coffee grounds with an appropriate ratio of room-temperature water, sealing it, and placing it in the refrigerator for cold extraction. When extraction is complete, we cannot directly pour and drink it - we must first filter out the coffee grounds using filter paper to obtain clean, particle-free coffee liquid before serving or drinking.

The principle is simple: because the extraction method is immersion, the coffee liquid is already mixed with large amounts of coffee grounds. If we don't filter them out with filter paper, the cold brew experience would be significantly compromised by the presence of numerous coffee grounds. Some friends might say: "Wouldn't using a dedicated cold brew bottle make this unnecessary step redundant?" Not necessarily! Why? Because although there are already cold brew bottles specifically designed for cold extraction on the market, most of these bottles come with filter screens that can separate coffee grounds. However, these filter screens cannot isolate all coffee grounds. To ensure water and coffee grounds can fully contact each other, the filter screen's pore size cannot be set too small.

This leads to many smaller coffee particles escaping through the filter screen during immersion - not just fine powder but particles larger than fine powder too. If we don't perform a second filtration after extraction, the excessive presence of coffee grounds will affect the overall coffee experience (depending on the cold brew bottle's filter screen used), resulting in a very rough mouthfeel. Therefore, after cold brew extraction is complete, FrontStreet Coffee uses filter paper for secondary filtration.

Ice Drip Coffee

Ice drip coffee is also a frequent user of filters. Generally, when making a pot of ice drip coffee, FrontStreet Coffee uses two circular filters. One is placed at the bottom of the filter cup, and another is placed above the coffee grounds (you can use two sheets or just one). Although they're all filter paper, they serve somewhat different functions because of their different positions.

The filter paper placed at the bottom of the filter cup primarily serves to filter coffee grounds, preventing them from entering the coffee; while the filter paper placed above the coffee grounds serves to distribute water droplets, reducing the penetrating force of falling droplets while evenly distributing this small amount of water to the coffee grounds below, ensuring all coffee grounds receive the same extraction.

Espresso Coffee

Espresso coffee can also use filters, and its applications are even more diverse. For example, we can place filter paper above the coffee puck, at the bottom of the portafilter, or set it at the liquid outlet. As FrontStreet Coffee mentioned earlier, they serve different functions in different positions. If we place filter paper above the coffee puck, then the filter paper's role during extraction is to evenly distribute hot water and reduce the coffee grounds that contact the shower screen, keeping the shower screen clean. (That's the theory, though the effect isn't particularly significant)

If we place filter paper at the bottom of the portafilter, then the filter paper's role during extraction would be: increasing the cleanliness of espresso. In the article "Why does coffee have 'tiger stripes'?" FrontStreet Coffee mentioned that because the portafilter's filtering capability isn't strong enough, some coffee grounds will seep out along with the coffee liquid. But when we place 1-2 sheets of filter paper at the bottom of the portafilter, it's equivalent to enhancing the portafilter's filtering capability, greatly reducing the amount of fine powder that can escape, allowing espresso to have a cleaner expression.

But it's worth noting that when we place filter paper at the bottom of the portafilter, the espresso extraction flow rate will increase due to the structural change. For example, FrontStreet Coffee's normal espresso extraction takes 30 seconds, but after adding filter paper, extraction time is reduced to 25 seconds. This 5-second difference causes significant under-extraction, so when placing filter paper at the bottom of the portafilter, we also need to adjust the grind. Finally, there's installing filter paper at the liquid outlet! Here, the filter paper's main role is: filtering out coffee oils.

If we want to make a more delicious Americano, removing coffee oils might be a good choice! This is a little "folk remedy" that FrontStreet Coffee shared before. Fine powder carried in coffee oils can increase coffee's bitterness and reduce cleanliness. Although adding filter paper in the portafilter can isolate large amounts of fine powder, it's troublesome because it changes coffee extraction! Therefore, if you want Americanos to have better performance without adjusting grind size, we can isolate oils and fine powder by placing filter paper at the liquid outlet. (But the filtration speed is too slow, so FrontStreet Coffee recommends using other filters with less efficient filtering performance)

Moka Pot

FrontStreet Coffee mentioned at the beginning that yesterday, a friend in the comments section asked whether moka pots need to use filter paper - it's optional, but mainly depends on how the final moka pot coffee will be used.

When our moka pot coffee is used for making black coffee, we can choose to place a filter paper on the coffee grounds bed, which can effectively block fine powder from seeping out, giving the coffee a cleaner taste - the principle is the same as using filter paper in coffee machines.

But if our moka pot coffee is used for milk coffee, then we don't really need to use filter paper. Because the presence of appropriate amounts of fine powder can increase coffee's body and make the coffee flavor more prominent, allowing it to compete with milk flavor. These are all the ways FrontStreet Coffee thinks filters can be used in coffee making. If there are other uses, feel free to add them in the comments below~~

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