What to Do When Cold Brew Coffee Filters Slowly? Efficient Cold Brew Filtering Techniques

Cold brew is enjoyable, but filtering takes forever. If you're someone who enjoys making cold brew coffee at home, you've likely encountered this frustration: Thinking it would be convenient, you prepared it last night to drink today, only to find that during the straining process, the coffee drips slower and slower. After more than ten minutes, the entire pot still hasn't finished dripping. Without guessing, the filter paper is definitely clogged by fine powder... What should you do?

The problem of slow cold brew filtration troubles many coffee enthusiasts. Office workers rushing out the door are almost running late, but the liquid level stubbornly refuses to drop. Finally, they have to use more filter paper and filter cups for straining, barely managing to filter the entire pot of cold brew clean.

Same Grind Size

Why does cold brew filtering take so much longer than pour-over?

Compared to the precise parameters of other hot water extraction methods, cold water immersion offers great compatibility. In a low-temperature, static state, unless significant adjustments are made, the coffee concentration won't change dramatically. Otherwise, subtle differences in grind size won't cause noticeable variations in the final flavor.

Generally, for the grind size of coffee used in cold brew, FrontStreet Coffee recommends using a setting similar to that for pour-over, which is medium-fine (with a #20 sieve pass rate between 70-85%, EK43s grinder setting at 9-10.5, or hand grinder C40 setting at approximately 20-22).

With this grind size, when we extract coffee using the pour-over method, we can typically control the drip time well. For example, with 15g of coffee, a 1:15 coffee-to-water ratio, and three-stage pouring parameters, the coffee usually finishes dripping within 2 minutes and 20 seconds. However, the same grind size in the cold brew filtering process takes much longer than this. Why?

Do you remember a comparison experiment that FrontStreet Coffee once conducted? At that time, coffee powders with two different grind settings were used for cold water immersion, with all other parameters unchanged. The results showed that the finer grind group had lower coffee concentration.

The reason is that the lighter fine powder particles easily become saturated with moisture first, then form clumping and adhesion phenomena. This initially reduces extraction efficiency, making the coffee taste weaker. During filtering, these clumped fine powder particles also clog the pores of the filter paper first, causing the drainage to become increasingly slow.

Are There Any Solutions?

1. Use non-woven filter bags for cold brew

Making cold brew involves just a few simple steps: grinding beans, adding water, stirring, sealing, refrigerating, and straining. If you want to wake up to a glass of iced coffee without waiting, we need to skip the straining step that requires patience. Based on FrontStreet Coffee's cold brew experience, using non-woven filter bags to hold the coffee powder during immersion is an excellent method.

Compared to the method of slowly waiting for filtration after immersion, using filter bags for cold brew certainly saves a lot of effort. FrontStreet Coffee conducted comparison experiments and found that coffee brewed with filter bags can still have full flavor characteristics, with even better fruit acidity than direct immersion. It's worth noting that the amount of coffee used for single immersion in tea bags should not be excessive, preferably controlled within 30g, otherwise water cannot make contact with the internal particles, resulting in weak coffee.

2. Can I directly filter the upper liquid without stirring?

Since the main culprit for slow cold brew filtration is fine powder, some might wonder: if we don't stir up those grounds before filtering and directly pour out the lighter-colored liquid from the top, could that solve the problem? To verify this claim, FrontStreet Coffee brewed two more pots of coffee to see whether "not stirring" is actually feasible.

Coffee beans: 25g Santa Vera
Water: 250g room temperature water (Nongfu Spring)
Grind size: EK43s grinder setting 9.5
Immersion time: 8 hours
Pre-immersion: Both stirred
Post-immersion: One pot stirred a few times before straining / One pot not stirred, directly strained

When directly comparing the two cups of cold brew, the coffee from the unstirred batch was noticeably lighter in color than the stirred one. The concentration measurements confirmed this (stirred group: 2.07%, unstirred group: 1.75%).

Left: Stirred group | Right: Unstirred group

In terms of taste, the unstirred Santa Vera cold brew had overall subdued aroma, felt watery, and had almost no distinct coffee flavor. In contrast, the filtered coffee after stirring was noticeably fuller, with sweet and sour notes of passion fruit, grape, starfruit, and lemon, along with a rounded tea-like quality. It tasted even more refreshing with its fruity acidity when served with ice. This shows that for optimal cold brew flavor, the stirring step cannot be skipped.

3. Place coffee grounds at the bottom first, then filter

This is a small technique FrontStreet Coffee discovered while researching materials, sourced from netizens with rich cold brew experience. The principle is to use larger coffee grounds as a medium to intercept fine powders, thereby keeping the filter paper's gaps clear and preventing severe clogging.

The operation steps are not complicated. First, stir the prepared cold brew thoroughly, then let it rest briefly for most of the grounds to settle at the bottom. Next, directly pour the upper liquid into a clean container, exposing the coffee grounds at the bottom. At this point, we need to scoop out 2-3 spoonfuls of grounds and create a layer inside the filter paper, then pour all the liquid into the filter cup and wait for filtration.

After testing, FrontStreet Coffee found that this method is indeed much faster than directly pouring the coffee slurry into the filter. A pot of cold brew with fine sugar grind consistency, about 250ml, can be completely filtered in about one minute.

FrontStreet Coffee
No. 10, Bao'an Qianjie, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473