I believe many people have had this experience: sometimes when brewing light-roast beans, it’s especially prone to water pooling. During the final pouring stage, you’ll notice the water level dropping very slowly—just won’t drain no matter what. The barista also suggests finishing the brew within a few minutes~ But if you wait, you’re afraid of over-extraction; if you don’t, it feels like the flavors will be incomplete... It makes pour-over brewing feel so stressful and tense.

Why is light-roast coffee more prone to water pooling and slower drainage? What should you do when you encounter water pooling at the end of pour-over? This time, FrontStreet Coffee is here to share with everyone the reasons why light-roast coffee tends to pool water, along with solutions for your reference. Hopefully, after understanding, you won’t misunderstand the beans anymore!

◆ High density (light roast is heavier)

Light-roast coffee contains more substances, making it heavier per unit volume, which means it has higher density. This means it’s more likely to sink in water~~

Because light roast involves lower roasting temperatures and shorter durations, there’s less thermal weight loss—about 10–13% (i.e., 100g of green beans yields 87–90g of roasted beans), whereas dark roast can exceed 18%. Therefore, light-roast beans are heavier! When the grind size of the grinder is the same, we can assume the volume is the same as a constant: 1. Then the formula for density is: density = mass ÷ volume

Light roast = (1 - 0.13) ÷ 1

Dark roast = (1 - 0.18) ÷ 1

Objects with higher density tend to sink, so it can be inferred that light-roast coffee is more likely to settle downward during brewing, causing filter holes to clog and slowing down the flow rate.

◆ Less volume expansion (light roast is denser, doesn’t expand as much)

During the roasting process, light-roast coffee expands less, meaning the cavities within the coffee cell walls are also narrower. They can’t hold as much gas produced during reactions as dark roast can, just like blowing up a balloon—the less gas inside, the harder it is to float.

Compared to the loose structure of dark-roast beans, which can hold more gas per unit volume and have longer degassing times during brewing, light-roast beans have a denser structure, higher unit density, less space for gas storage, and shorter degassing times, making them harder to float.

◆ Light-roast beans are ground finer

As mentioned earlier, light-roast beans lose less weight, expand less, and thus have higher density and a denser structure. When grinding light-roast beans, a finer grind size than dark roast is needed to fully extract the flavor molecules of the coffee. Finer coffee grounds leave smaller gaps for water to pass through, naturally slowing the flow rate. In the final stage of pour-over, the amount of coffee liquid that can seep through the side of the coffee bed and pass through the filter paper gradually decreases. The remaining pooled water can only honestly flow out by passing through all the coffee grounds, making water pooling more likely.

So, what should you do when you encounter water pooling at the end of pour-over?

① Discard it The longer the extraction time, the more likely over-extraction is to occur, pulling out unnecessary and undesirable woody fiber flavors, resulting in bitterness. And most of the essence is actually extracted early on. The efficiency of extraction in pour-over coffee decreases the longer it goes, and the fewer flavor compounds can be extracted. So, the final pooled water actually has a light flavor and isn’t very good (you can try catching some of the leftover liquid and tasting it yourself if you don’t believe it). The final light coffee liquid mainly serves to dilute and adjust the concentration, so discarding it isn’t a waste. You just need to add a bit of water to the extracted coffee liquid to achieve the same concentration and taste.

② Grind coarser The main reason for water pooling is still that the grind is too fine or there’s too much fine powder, clogging the filter paper pores. So, you might as well rebalance the water temperature, grind size, and stirring. Grind coarser, then increase the water temperature, and add appropriate stirring. This can prevent water pooling and achieve a similar extraction effect.

③ Sift out fine powder Sometimes water pooling is caused by poor-quality grinders producing too much ultra-fine powder. So, just buy a simple sifter on Taobao, sift out the ultra-fine powder slightly before brewing, and the problem will be significantly improved. If you’re worried about wasting the sifted ultra-fine powder, you can re-add it to the filter cup for brewing before the final pour, so nothing goes to waste and it won’t clog~

There are many ways to make coffee taste better. FrontStreet Coffee believes understanding the logic behind it is also important. Next time you encounter this situation, try tasting the flavors first to see if there’s anything you dislike, then define whether there’s room for improvement in the brewing process!