What Mesh Size Should Be Used for Pour-Over Coffee Metal Filters? What Are the Differences Between Metal Filters and Filter Paper? How Many Microns Does 400 Mesh Equal?

Because of their excellent comprehensive performance, paper filters have become the mainstream filter material for pour-over coffee today. However, paper filters are not the only filtering material available. In addition to paper filters, there are also filtering tools made from other materials such as flannel and metal.

Different materials have different characteristics and properties. To brew a good cup of coffee using filtering tools made from different materials, we need to first understand their characteristics and properties. Since there's already plenty of information about flannel filters, today FrontStreet Coffee will share how to use a metal filter to brew a good cup of coffee~

Advantages and Disadvantages of Metal Filters

The metal filter that FrontStreet Coffee has is just one randomly purchased online, with a mesh size of 400. It looks like an inverted cone with a flat bottom. The filter itself has two layers - the inner layer is a 400-mesh filtering metal screen, while the outer layer simply serves a fixing function.

400 mesh corresponds to a particle size of 38 micrometers, which can be considered a very small pore size. Therefore, even if the coffee grounds are shaken after pouring, very few coffee grounds will fall through the filter. However, this pore size is still larger compared to paper filters. This brings us to one of its advantages - like flannel, it can retain coffee oils, which is a significant enhancement for coffee. Because coffee oils contain some oil-soluble aromatic substances, their presence adds certain aromas to the coffee. At the same time, oils can also increase mouthfeel, giving the coffee a fuller body. This is an advantage that paper filters lack, as their filtering performance is too strong, filtering out oils along with other substances.

In addition, metal filters have another advantage - they are environmentally friendly and cost-effective because they are reusable. Like flannel filters, they only need to be rinsed and dried after use before they can be used again. Calculated based on one cup per day, the cost of the filter can be recovered in about 100 days, which is very economical. Now that we've discussed the advantages, let's talk about the disadvantages! The disadvantages of metal filters, like their advantages, come from their filter pores. Although metal filters can release oils to enhance the aroma and mouthfeel of coffee, they can also let coffee grounds through. Because coffee particles smaller than 38 micrometers are abundant, they can easily pass through the filter, affecting the texture and taste of the coffee.

If the grinding quality of your grinder isn't high enough and you plan to use a metal filter for coffee brewing, it's best to use a flour sifter to remove some fine grounds before brewing. Otherwise, the negative impact of excessive fine grounds should not be underestimated. That's roughly it, so next FrontStreet Coffee will use a metal filter to brew coffee and share some things we need to pay attention to during the process~

Brewing Guide

Before starting the brewing process, FrontStreet Coffee would like to insert a note: The flow rate of a metal filter increases as the water level rises. What does this mean? It means that when you pour water to a higher level, its flow rate will be faster. Through testing, FrontStreet Coffee found that the flow rate of metal filters at high water levels is much faster than V60. And too fast a flow rate will reduce the contact time between water and coffee grounds, easily leading to under-extraction. Therefore, during brewing, we need to reduce the pouring rate to prevent the coffee bed and water level from being raised too high, which would cause the flow rate to be too fast, leading to risks of under-extraction such as thin mouthfeel and bland taste.

For this brewing, FrontStreet Coffee used Yirgacheffe washed beans - Guddina, with extraction parameters consistent with those used with paper filters:

• Coffee amount: 15g
• Grind size: EK43 setting 10, with 80% passing through a #20 sieve, approximately fine sugar size
• Coffee-to-water ratio: 1:15 (15g coffee with 225ml hot water)
• Brewing water temperature: 92°C
• Pouring method: Three-stage pour

The first step is still the bloom, where we first use twice the amount of coffee grounds in water for a 30-second bloom.

After the bloom ends, we pour the second stage of hot water (in large circles), totaling 120ml. Because we need to prevent the water level from rising too high, we should pour with a small water flow at this point. At the same time, when circling, be careful to avoid the water stream hitting the edge of the filter, as this will cause bypass water.

When the coffee liquid has completely permeated, we also pour the third stage of hot water with a small flow, totaling 75ml. Since the extraction focus of this stage of hot water is the bottom layer of coffee grounds, we need to reduce the circling range, focusing on extracting the bottom layer of coffee grounds in the center.

When the coffee liquid has finished permeating, we can remove the filter cone and end the extraction! Total time was 2 minutes and 5 seconds, about 10 seconds faster than brewing Guddina with a paper filter. The taste performance was very good - delicate white floral notes, fresh lemon, and a clean green tea aftertaste, which is a very authentic Yirgacheffe flavor. In terms of mouthfeel, due to the presence of oils, this cup of Guddina has an even more outstanding body, with a longer aftertaste, which is quite excellent~

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