How to Brew Coffee with Boiling Water? What Happens When You Use 100°C Boiling Water? What's the Ideal Water Temperature for Pour-Over Coffee?

Two weeks ago, FrontStreet Coffee discussed the question of "what water temperature makes the best coffee." In that article, FrontStreet Coffee mentioned in detail that water temperature is not the only parameter that determines whether coffee tastes good. Other parameters such as coffee grind size and extraction time are also equally important. Even if you use extremely high or low water temperatures, as long as other parameters are properly matched, you can still brew a delicious cup of coffee.

So, some friends privately messaged FrontStreet Coffee asking, based on this reasoning, can boiling 100°C water also be used to brew delicious coffee?

Absolutely! In fact, in the comments section of that article, some friends mentioned that Taiwanese barista Amis uses 100°C boiling water to brew coffee. Not only that, but coffee experts like James Hoffman and Scott Rao have also shared how to use 100°C boiling water to brew coffee. So we can know that 100°C boiling water can indeed be used for brewing coffee. The reason why we rarely see people using 100°C boiling water to brew coffee in daily life is simply because the extraction efficiency of 100°C water is too high. Using conventional brewing methods can easily dissolve excessive bitterness, astringency, and other undesirable flavors from the coffee, making it relatively unforgiving.

Therefore, if we want to brew a good cup of coffee using 100°C boiling water, we need to adjust other parameters or methods in the brewing process to avoid over-extraction. The most common approaches are to shorten the extraction time or use a coarser coffee grind - both are excellent choices. This is because most undesirable compounds are large molecules that dissolve more slowly compared to desirable compounds. By shortening the extraction time, we can effectively inhibit the release of these undesirable substances. Using a coarser grind reduces the surface area of coffee particles exposed to water (compared to fine grinding) and the amount of fine particles, which gives the boiling water a higher margin for error and results in less bitter compounds in the brewed coffee.

In addition, we can also use specific pouring techniques to complement 100°C water temperature to brew delicious coffee, such as the stirring method commonly used by Amis, or one-pour techniques. These brewing methods share a common characteristic: they all feature "immersion-style extraction." The characteristic of immersion-style extraction means that the liquid concentration doesn't continuously refresh, and extraction efficiency continuously decreases as concentration increases. French press and clever dripper are representative devices for immersion-style extraction. Those who have used them know that regardless of how high the water temperature is or how long the immersion time is, coffee rarely becomes over-extracted. This is because when the liquid concentration reaches a certain level, its extraction efficiency becomes extremely low.

Methods like the stirring technique, one-pour, and single-injection all involve pouring a large amount of hot water at once during certain stages, causing the water injection rate to exceed the infiltration rate. This causes hot water to accumulate in the filter cone, creating "immersion-style extraction" in a short time. Then, due to the continuously increasing liquid concentration in the cup, extraction efficiency continuously decreases. Therefore, even with water as hot as 100°C, this immersion characteristic makes it less likely to brew over-extracted coffee.

However, it's worth noting that it's "less likely" rather than "impossible" to brew over-extracted coffee. When coffee is roasted too dark or the bean quality isn't high enough, 100°C boiling water can still easily produce over-extracted coffee that is both bitter and astringent. Therefore, we should try to avoid using 100°C boiling water to brew overly dark roasted or lower quality beans. Next, FrontStreet Coffee will demonstrate how to brew a good cup of coffee using 100°C boiling water.

Brewing Demonstration

Since some friends left comments wanting to try the stirring method for pour-over, FrontStreet Coffee will use the stirring method for today's brewing demonstration. The coffee beans used this time are Sidamo ALO, a light-medium roast that can withstand boiling water temperature without being "scalded" (just kidding)! The extraction parameters are as follows:

Coffee amount: 15g
Grind size: Ek43 setting 7, with 90% pass-through rate on #20 sieve (originally used 92°C three-stage pour with grind setting 10 and 75% pass-through rate on #20 sieve)
Water temperature: 100°C (originally 92°C for three-stage pour)
Coffee-to-water ratio: 1:15
Brewing method: Stirring method (worth mentioning: FrontStreet Coffee will use a regular kettle directly for brewing this time because the pour-over kettle FrontStreet Coffee uses doesn't have temperature control. Hot water needs to be heated in another kettle before being poured into it. And 100°C boiling water will definitely cool down due to heat absorption when poured in. So to ensure brewing accuracy, FrontStreet Coffee will use the kettle directly for brewing this time~ Therefore, this article could also have another title: How to use a kettle to brew coffee)

It's best to prepare all materials in advance so we can start brewing immediately when the water reaches 100°C!

The entire pouring process is mainly divided into two stages! For the first stage, we need to pour 90ml of hot water quickly all at once after starting the timer! (Actually, once you have the right parameters, you don't need to time it)

Immediately after pouring, use any tool to stir - 10 back-and-forth stirs or 10 circular motions will suffice.

When all the coffee liquid in the filter cone has completely filtered through, pour all the remaining hot water at once. The pouring here can be slower - just normal large-flow pouring is fine. After pouring is complete, simply wait for all the coffee to drip through, and you can end the extraction. No doubt, it's that simple!

Total extraction time was 2 minutes and 15 seconds! Although the extraction time was longer than before, the grind was finer than before, and the water temperature was higher than before. However! The coffee showed no signs of over-extraction. The refractometer showed an extraction rate close to 21%, and the coffee had a noticeably rich juiciness - sweet and sour with prominent mango, pineapple, and citrus flavors, with an oolong tea finish! FrontStreet Coffee shared it with several customers present and received unanimous praise.

FrontStreet Coffee can confidently say that this cup of coffee brewed with 100°C boiling water is completely on par with coffee brewed using conventional methods. So we can know that as long as parameters or methods are properly managed, brewing a delicious cup of coffee is easily achievable~ Practice reveals truth, everyone can also try this at home!

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