Does Repeatedly Boiled Water Hurt Flavor in Coffee Brewing

Repeatedly boiling the same water before coffee brewing does not automatically ruin the cup. A controlled test compared water boiled one, two, three and four times, tracking both the water TDS and the coffee concentration of each batch. The brewed coffee used a medium-light roast Sidamo Huakui 8.0, prepared with the clever cup immersion method to limit variation from pouring technique.

The setup paired a TDS test pen for water quality with a coffee concentration meter for the finished drink. By holding the coffee and method constant and changing only the boil count, the experiment isolated whether reheating water shifts extraction enough to notice in the cup. For anyone wondering whether boiled coffee tastes diminished, the comparison offers data rather than guesswork.

When brewing coffee, most people focus on whether the water's TDS is in the appropriate range, but few pay attention to whether repeatedly boiling hot water affects the coffee's flavor. Some believe that coffee brewed with water that has been boiled multiple times will have a decline in quality. To verify this claim, Front Street designed a controlled experiment, using a TDS test pen and a coffee concentration meter, brewing a medium-light roast Sidamo Huakui 8.0 by the clever cup immersion method, using water boiled for the first to the fourth time respectively, and recording the TDS value of the water and the coffee concentration performance each time. This article will present the experimental setup, operating procedure, and data results one by one, to help coffee lovers determine whether repeatedly boiled water is really unsuitable for brewing coffee.

Generally speaking, everyone's requirements for coffee brewing water mainly focus on the TDS value, such as what range the TDS should fall into to be suitable for extracting coffee. Surprisingly, however, in addition to TDS, the number of times hot water has been boiled has also become an indicator some friends care about. They feel that compared with coffee brewed with fresh water after the first boil, coffee brewed with hot water that has been repeatedly boiled or boiled more than twice will have a diminished taste. Is repeatedly boiled water really unusable for brewing coffee? Is this claim reliable? To get to the bottom of it, Front Street specially conducted a round of experiments to verify whether repeatedly boiled water is indeed unsuitable for coffee brewing.

Brewing Experiment

First, let's bring out the two important "helpers" for this experiment. To make the results more objective, in addition to relying on taste judgment, precise data support is also needed. They are: a TDS test pen that can detect water quality, and a concentration measuring device that can measure coffee concentration. By comparing coffee brewed with water boiled different numbers of times, we can see whether the taste is really affected.

Because this experiment involves many rounds, it is necessary to reduce interference from human operation as much as possible. Therefore, Front Street did not use the pour-over method this time, but chose the clever cup to make the coffee. The clever cup only requires pouring coffee grounds and hot water in to soak, without manually controlling the water flow or stirring, and it can still extract coffee with suitable concentration and extraction yield, making it more than suitable as the extraction tool for multiple experiments.

At the same time, to ensure the experiment stays close to reality, after each pot of hot water was boiled, Front Street immediately made the coffee, then let the remaining hot water cool to room temperature before measuring TDS (because the TDS pen cannot measure high-temperature water), and then continued to repeat boiling and brewing. The beans used this time were a medium-light roast Sidamo Huakui 8.0. The specific parameters were: 15g of coffee grounds, grinding degree set to 9.5 on the Ek43, fine granulated sugar coarseness, 85% passing rate through a No. 20 sieve, coffee-to-water ratio 1:15, water temperature 94°C, and immersion time 4 minutes. First, place a trapezoidal filter paper, then pour in the coffee grounds and hot water in sequence.

Then take out the stirring spoon and stir in circles 10 times, so that the water and coffee grounds fully contact.

After waiting 4 minutes, remove the container and place the clever cup on it, allowing the coffee liquid to filter out.

After filtration is complete, measure the coffee concentration and conduct tasting respectively.

Afterward, let the coffee cool, and keep a small portion for the TDS test. The remaining hot water is boiled again and brewed again, repeating this cycle until the fourth brewing is completed.

The water source used by Front Street is Nongfu Spring. Measured with the TDS test pen, the TDS values of the water boiled for the 1st to 4th times are as follows: First boil: 34

Second boil: 38

Third boil: 43

Fourth boil: 47

The above content is compiled by CoffeeHunters, a coffee news website.