Should Moka Pots Use Cold or Hot Water? Why Does Moka Pot Coffee Splatter? Why Is Moka Pot Coffee Bitter?

Compact, simple, and affordable—thanks to these three advantages, the moka pot has become an essential coffee brewing tool for many households. Recently, FrontStreet Coffee has received many private messages about a hotly debated moka pot question: when making moka pot coffee, should you use hot water or cold water?

As we know, in common coffee extraction methods like pour-over, French press, and espresso, water temperature determines the dissolution rate of flavor compounds. The higher the water temperature used for extraction, the faster flavor compounds dissolve, and vice versa. This principle also applies to moka pots, but temperature affects not the dissolution rate of flavor compounds, but rather the heating time! The working principle of a moka pot involves heating the water in the bottom chamber to create steam, which then compresses the internal space and pushes hot water upward through the coffee grounds to extract coffee.

Therefore, the water temperature primarily determines the heating duration. When we use hotter water, the heating time is shorter, and the moka pot begins to extract earlier; conversely, when we use colder water, the heating time is longer. But did you know that besides the heating duration, different water temperatures also affect the taste of moka pot coffee? Next, FrontStreet Coffee will conduct an experiment to demonstrate the differences between these two approaches.

Moka Pot Experiment

The experiment is quite simple. FrontStreet Coffee will use cold water and hot water respectively to brew moka pot coffee. All extraction parameters will be identical except for water temperature, allowing us to observe the differences in extraction time and resulting coffee flavor. The coffee bean used for this experiment is FrontStreet Coffee's Sunflower Warm Blend. Its medium-dark roast and prominent flavor profile make it perfect for this experiment. The extraction parameters are as follows:

• Coffee dose: 19g
• Coffee-to-water ratio: 1:8
• Grind size: Setting 1 on Galileo Q18, flour-like consistency
• Water temperature: Cold water group at 20°C, hot water group at 100°C

Both operations are identical: first, pour the specified amount of water into the moka pot's lower chamber.

Then, fill the coffee grounds into the filter basket and attach it to the water chamber.

After tightening the upper chamber, place it on the stove for heating.

The moka pot using cold water began to extract at 5 minutes and 31 seconds; while the moka pot using hot water began extracting at 2 minutes and 44 seconds. We then waited until the extracted coffee filled the upper chamber before removing it from the heat source. (Moka pot extraction using cold water ↓)

(Moka pot extraction using hot water ↓)

From the two images above, we can observe that the moka pot using cold water showed splattering during the extraction phase, which is not ideal. This likely indicates channeling in the extraction. Next, we'll pour both coffees for tasting.

As expected, FrontStreet Coffee could detect a faint bitterness in the aftertaste of the moka pot coffee made with cold water. In contrast, the moka pot coffee made with hot water performed exceptionally well, with prominent berry sweetness and acidity, whiskey-like aroma, and butter cookie flavors, with essentially no negative characteristics. After measurement, the extraction rate of the cold water moka pot coffee was about 2% higher than the hot water version. After diluting with water, both coffees' flavors opened up, and FrontStreet Coffee could more directly perceive the differences!

So, why would changing just the water temperature create such significant differences? The explanation is quite simple: cold water requires longer heating time, and this heating process affects the coffee grounds. The prolonged heat causes gaps between grounds to expand, creating channels. During subsequent extraction, hot water naturally concentrates through these channels due to inertia, resulting in uneven extraction. In conclusion, we can determine that using hot water for moka pot extraction not only reduces heating time but also minimizes channeling caused by heating the coffee grounds, resulting in coffee less likely to exhibit negative characteristics. However, FrontStreet Coffee isn't saying that moka pots cannot use cold water—after all, hot water isn't always available. But when using cold water, it's best to grind the coffee finer to increase resistance and reduce the negative effects of prolonged heating.