What is the Correct Water Temperature for Espresso Brewing? At What Temperature is Coffee Best Brewed?

Previously, when FrontStreet Coffee shared knowledge related to espresso extraction, we focused on how parameters such as dose, ratio, grind, time, and pressure affect extraction. Additionally, we emphasized operational techniques for steps like dosing, distributing, tamping, and locking the portafilter. The only aspect that FrontStreet Coffee consistently glossed over was water temperature.

This doesn't mean that water temperature isn't important. Rather, adjusting water temperature on many coffee machines can be quite troublesome, so FrontStreet Coffee simply sets it as a fixed value and then adjusts other parameters to work with this fixed temperature to extract delicious espresso.

In recent years, with the popularity of complex operations like pressure profiling, coffee machine water temperature has also become a frequently adjusted parameter. However, it's important to understand that unlike pour-over coffee brewing, changes in coffee machine extraction temperature can have numerous effects.

What Does Coffee Machine Water Temperature Affect?

As is well known, the greatest impact of water temperature on extraction is efficiency. When using higher water temperatures, extraction efficiency is higher, and flavor compounds in coffee are quickly dissolved. When using lower water temperatures, extraction efficiency decreases accordingly, and the dissolution rate of flavor compounds slows down.

Besides extraction efficiency, coffee machine water temperature also affects the flow rate of coffee liquid, or rather, the drainage speed. With other parameters being equal, the higher the extraction water temperature, the relatively slower the coffee liquid flow rate. Conversely, the lower the extraction water temperature, the relatively faster the coffee liquid flow rate.

Those who have seen FrontStreet Coffee's recent posts know that this is because water temperature determines the rate of puck expansion and degassing. High temperatures can cause the puck to expand more quickly and release various substances hidden within the coffee grounds. The expanded puck reduces gaps between coffee grounds, while released gases are enveloped by coffee bean lipids to form bubbles, creating resistance to water flow. Under the combined effect of these factors, the coffee flow rate is thus altered.

If you still don't understand this principle, why not experience it through practical operation? When we turn on our machines every morning, the coffee machine needs nearly 20 minutes to heat the boiler and generate steam. During this time, the coffee machine's extraction function is operable, but the water temperature is relatively low, typically around 60°C.

Therefore, we can try extracting espresso at lower temperatures during that time to see what state it produces. We would then find that the coffee liquid flow rate is quite fast. This is because carbon dioxide emission is insufficient and the puck expansion rate is inadequate, so the flow rate becomes faster.

The final factor affected by water temperature is the richness of crema. As FrontStreet Coffee mentioned earlier, water temperature affects the emission rate of carbon dioxide, and carbon dioxide is the main component of crema. Therefore, with other parameters unchanged, the higher the water temperature used, the richer the extracted crema will be, and vice versa.

What Water Temperature Is Most Suitable?

The above are the effects that different water temperatures bring to espresso extraction. So the question arises: what water temperature should we use to extract the most suitable espresso?

Actually, just as FrontStreet Coffee shared in the post "What Temperature Water Makes the Best Tasting Coffee," besides water temperature, grind, ratio, and time are all main parameters that affect coffee extraction. Therefore, the specific water temperature to use still needs to be coordinated with these factors.

In the book "The Science of Espresso Extraction," there is such a hypothetical experiment: Italian baristas prefer to use water at 85-91°C to extract espresso, while American baristas prefer to use water at 92-96°C to extract espresso.

The reason for this difference mainly lies in their different ratios. The Italian standard uses 7 grams of coffee grounds to extract 1 ounce of espresso, while America uses 18-21 grams of coffee grounds to extract 1 ounce of espresso. The ratios, times, and grinds are all different, so the water temperatures they use are also different.

Conversely, as FrontStreet Coffee mentioned at the beginning, you can also set water temperature as a fixed value and then adjust other parameters to work with this fixed temperature.

Generally, the initial water temperature of coffee machines when they leave the factory is set in the range of 92°C-96°C. This range is a very suitable temperature range—neither too low nor too high. As long as the coffee machine's initial water temperature is within this range, unless you have special extraction needs, we can almost leave it unchanged.

Then, by applying the golden espresso extraction formula (1:2 coffee-to-liquid ratio, 25-35s extraction time) to fix the liquid weight and time, we can quickly extract delicious espresso by adjusting the grind and fine-tuning the liquid weight.

Important Considerations

It's worth mentioning that... just like with pour-over coffee, the water temperature we can set now is the temperature inside the boiler, not the actual temperature during extraction. Because water passes through various pipes from the boiler to the shower screen, the final actual extraction temperature will be several degrees different from the set temperature due to heat absorption.

Particularly when there hasn't been espresso extraction for a long time, the difference between water temperature and the set temperature will be greater. Therefore, when the interval between coffee extractions is too long, it's best to flush hot water once before locking the portafilter. This not only helps us calibrate the water temperature but also cleans the shower screen, removing "residual debris" (that is, coffee grounds) attached to it.

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