How to Perform Pour-Over Coffee Stirring? What is the Slurry Flow Brewing Method? What to Do When Coffee Grounds Are Too Fine?

Have you ever had this happen? After brewing, the coffee grounds in the filter fail to form the usual well-defined crater and instead leave a sticky, muddy "pit" like the one below.

This is what FrontStreet Coffee often holds up as a negative example. A muddy pit is caused mainly by grounds being ground too fine, or by poor grinding quality from the grinder (too many fines), producing this unintended result - though some people deliberately create muddy pits. An accidental one is undesirable, because it usually signals that the coffee will taste over-extracted. The fine grind drags out the extraction time, which in turn pushes the extraction rate beyond the optimal range. That is why, when people ask FrontStreet Coffee stores about bitter or over-extracted home brews, we always ask first about the extraction time and the appearance of the coffee bed at the end.

If it is only our own ground coffee, that is manageable - grind too fine this time, adjust coarser next time. But what if you have bought pre-ground coffee that is extremely fine and the water flows very slowly? When the grind is fixed, do we have no choice but to accept over-extracted coffee or throw the batch away?

Obviously not. There is no need to despair. If normal methods cannot brew this coffee well, we simply need a different approach.

How to Fix Coffee Grounds That Are Too Fine

There are two solutions. The first is to abandon pour-over altogether and use an immersion method such as a French press or a Clever Dripper. Immersion's high fault tolerance keeps the extraction rate from running past the optimal range. For the technique, refer to our article on immersion extraction and apply those ideas directly. But if we want to present this coffee using pour-over, we need to start with the theory.

Coffee has a broadly accepted delicious extraction range: 18%-22% under Golden Cup extraction theory. It is not absolute, but most delicious coffees do fall inside it. To land the brew in that range, we must control the extraction efficiency of our parameters, letting water pull the right amount of the desired compounds. The efficiencies are cumulative, like 1+1+1+1=4. Change any one term and the overall extraction efficiency changes.

For example, FrontStreet Coffee's parameters for brewing 15g of light roast coffee are: a 1:15 coffee-to-water ratio, a grind consistency similar to coarse sugar, a water temperature of 92°C, and an extraction time of 2 minutes. With these parameters, the brewed coffee has an extraction rate of 20%. Keep the other parameters the same but grind finer, and the final extraction rate rises to 23%. The finer grind also affects time: as noted above, slower flow extends the extraction time, which pushes the final rate up even further. This should be easy to follow.

So to bring the extraction rate back to 20% when the grind is too fine, we should reduce the extraction efficiency of the other three parameters - lowering the water temperature, reducing the water amount, or shortening the extraction time. That much is straightforward. If the grind is so fine that the coffee bed becomes a muddy puddle, though, those conventional adjustments will not help much. With the grounds that fine, the gaps between particles shrink, making it hard for hot water to pass through; the flow speed will not slow but will in fact increase sharply, extending the extraction time. Meanwhile, lowering the water temperature prevents some compounds from dissolving fully and compromises flavor.

In such cases, FrontStreet Coffee would recommend a "high concentration, low extraction" approach: use a small amount of hot water to extract most of the compounds from the coffee. The limited water is enough to restrain how much the grounds release, so even with a longer extraction time, over-extraction is less likely. The remaining task is to figure out how to coax the compounds out with that small amount of water. Recently a distinctive method well suited to this has become popular: "Slurry Flow." As FrontStreet Coffee mentioned earlier, some people deliberately create muddy pits - this refers to that technique. Grind the coffee to a flour-like consistency, then use high concentration with low extraction combined with stirring so the compounds dissolve quickly in a short time. Finally, add extra hot water to dilute the concentrate, and you easily get a pour-over with full flavor and a proper extraction rate.

FrontStreet Coffee has tried this several times, and it is indeed a very practical method, especially when the grounds are ground too fine. Next, FrontStreet Coffee will share how to do it.

How to Carry Out the Slurry Flow Method

To show the method's effect clearly, FrontStreet Coffee will use an espresso-grade, flour-like grind for this demonstration, with Papua New Guinea Bird of Paradise beans. The parameters are: 15g dose, espresso-grade flour-like grind, 1:10 coffee-to-water ratio, 88°C water temperature, stirring method, and a V60 dripper (best paired with a fast-flow dripper). Remember to prepare an extra chopstick or spoon for stirring. With 15g at 1:10, we need 150ml of hot water, split into two pours: 30ml for the bloom and 120ml for the second pour. First, pour 30ml of hot water for a 30-second bloom. (It helps to dig a small hole in the center of the bed with a spoon beforehand so water penetrates better.)

Right after pouring the bloom water, stir the coffee bed with a spoon, because the grounds are so fine that hot water struggles to saturate every particle.

When the bloom ends, pour all the remaining 120ml of hot water at once, stirring as you go.

Keep stirring until the water level drops to half the dripper, then stop. All that is left is to wait for the coffee to finish dripping. Remove the dripper, add 70ml of hot water to dilute the coffee, and you can start enjoying it.

Measured afterward, this coffee's extraction rate landed at 21% - a quite thorough extraction. The taste is pleasant, with absolutely no negative signs of improper extraction. Acidity, sweetness, and bitterness are harmoniously balanced, the flavors are prominent, and the mouthfeel is rich. If you have accidentally ground your coffee too fine, why not give this distinctive method a try?

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FrontStreet Coffee Recommendation

Since this article demonstrates the Slurry Flow method with Papua New Guinea Bird of Paradise, that is a natural bean to start with. FrontStreet Papua New Guinea Bird of Paradise comes from the Sigri region and is often called "Little Blue Mountain" because its texture resembles Jamaican Blue Mountain. Grown at 1600-1800 meters in volcanic soil, it uses the same Typica variety as Blue Mountain and meets the high AA grade, with plump beans and very few defects. Its triple washed fermentation gives a clean, pure cup with a pronounced sweetness - an excellent choice for anyone who prefers a low-acid coffee.

If you would rather practice with a more forgiving everyday bean, FrontStreet Ethiopia Yirgacheffe Gidding is a good match. This washed Yirgacheffe, from a cooperative of about 300 farmers in the Worka area, shows clear citrus, berry, and floral notes with a green-tea-like finish. Its gentle, bright acidity makes it easy to brew and easy to enjoy while you dial in a new technique.