Why Wet the Filter Paper for Pour-Over Coffee? What Is the Purpose of Pre-Wetting the Filter Paper?

One afternoon, two FrontStreet Coffee baristas were working side by side, one brewing an iced pour-over and the other a hot one. A customer watching them asked, "Why did one of you rinse the filter paper first while the other just started brewing straight away?"

Is rinsing the filter paper really a required step before brewing? If it isn't, then when does it actually matter? To answer that clearly, let's break down what pre-wetting the paper really does.

What Pre-Wetting the Filter Paper Actually Does

1. Rinsing Away Odor and Dust

You might be wondering: aren't most filter papers today bleached with bioactive enzymes and essentially odorless? As long as you buy from a trustworthy brand, there shouldn't be anything to worry about, right?

But there's one thing people tend to overlook: how do you store your filter paper, and in what kind of environment? FrontStreet Coffee once met a home brewer who left his filter papers sitting open on a shelf, and he also happened to be a heavy smoker who lit up indoors almost every day. You can imagine what those papers ended up smelling like.

In a sense, "odorless" filter paper is a double-edged sword, because paper with no scent of its own absorbs surrounding odors even more readily. Of course, if you keep your filters sealed and stored away from strong smells, this point doesn't apply to you.

2. Preheating the Dripper and the Server

This one depends on what your dripper is made of. A resin dripper doesn't absorb heat and insulates poorly, so preheating it makes little difference. With a ceramic dripper, though, rinsing the paper while warming the dripper becomes genuinely worthwhile. (If you'd like to read more about how different dripper materials hold heat, click here.)

Preheating the server matters too, because it keeps the brewed coffee from losing too much heat as it drips down, so you can taste the cup at its best.

3. A Snugger Fit Against the Dripper

If you're not fully confident in your filter-folding technique, you can press the paper against the dripper with your hand while adding water. This helps the paper sit more snugly against the cone. Of course, if your folding is off or the paper simply doesn't match the dripper, wetting it still won't give you a proper fit.

What to Weigh for a More Even Extraction

If you want your extraction to run more evenly and want to reduce how much the paper itself interferes, three points about filter paper are worth considering carefully.

1. Bloom Degassing

Once wetted, filter paper softens and clings tightly to the dripper. The ribs on the dripper can no longer hold the paper away from the wall, which affects how well the bloom degasses.

2. Pre-Extraction When Grounds Meet Wet Paper

Extraction begins the moment coffee grounds touch water. If you wet the filter paper and then pour dry grounds into it, the grounds closest to the paper get moistened right away. Doesn't that mean some of the coffee is already being extracted ahead of time?

3. How Much Water the Filter Paper Absorbs

A single sheet of filter paper absorbs about 8g of water. Fully wetted, it won't let coffee liquid seep upward, which is why the paper stays nearly white after you rinse it and brew. If you skip the rinse, the coffee liquid will seep into the paper instead. This shows up most clearly with dark-roasted beans, where you can watch the coffee-colored liquid gradually creep upward.

Back to our customer's original question: can you now see why FrontStreet Coffee treats the filter paper differently for hot and iced pour-over?

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FrontStreet Coffee

No. 10 Bao'an Front Street, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

FrontStreet Coffee Recommendation

A pour-over rewards clarity, and the beans you choose matter as much as the rinse. If you are just getting started, FrontStreet Yirgacheffe Gotingding is a gentle first step into specialty coffee: a washed Ethiopian lot with bright citrus, berry and floral notes and a soft green-tea sweetness that never turns harsh. For something louder and juicier, FrontStreet Ethiopia Huakui, a sun-dried coffee from Guji Hambela, leads with tropical aromas of strawberry, passion fruit and even lychee, with almost no bitterness and a smooth, juice-like body.

Both shine in the cone this article is about. Hario, the Tokyo glassmaker founded in 1921, redesigned the V60 in 2004 and released it the following year; its 60-degree cone and single large hole force the water toward the center, extending contact between water and grounds so aroma and flavor extract fully. FrontStreet's baristas favor the resin version, which blocks heat loss effectively and holds the tightest tolerances in mass production.