How Water Temperature Affects Espresso Extraction

Water temperature plays a key role in espresso extraction. Understanding how does the espresso machine work helps you see that higher temperatures increase extraction efficiency, dissolving flavor compounds more quickly, while lower temperatures slow the process. Temperature also affects flow rate: with other variables fixed, hotter water tends to slow the flow, and cooler water speeds it up. This influences crema richness and overall flavor balance in the cup.

Espresso and Americano do not prefer the same temperature range due to differences in dose and ratio. Rather than constantly adjusting temperature, you can lock it within a reasonable range, such as around 92 degrees Celsius, and adapt by changing grind size and liquid weight. Also note that boiler temperature may deviate from actual extraction temperature, and long intervals between shots can affect stability.

When extracting espresso, what temperature should the water be set to? This article starts from Front Street's hands-on experience and systematically sorts out the specific effects of water temperature on extraction efficiency, the flow rate of the coffee liquid, and the richness of the crema, and also explains, in light of the differences between espresso and Americano in dose and ratio, why the two do not prefer the same water temperature range. The article will also introduce a practical approach: fix the water temperature within a reasonable range, and instead adapt by adjusting the grind and the liquid weight, so as to quickly and stably extract a delicious espresso. In addition, the article also gives specific explanations about the deviation between boiler water temperature and actual extraction water temperature, as well as how to respond when the interval between extractions is too long.

However, this does not mean that the water temperature is insignificant; it is just that adjusting the water temperature on many coffee machines is rather cumbersome, so Front Street simply locks it to a fixed value and then relies on adjusting other parameters to work with this fixed water temperature, thereby extracting espresso with a satisfying flavor.

In recent years, more complex operation methods such as pressure-profiling extraction have gradually become popular, and the water temperature of the coffee machine has accordingly become a variable that is often changed. But it should be noted that the impact caused by changes in the coffee machine's extraction water temperature is not the same as that of pour-over brewing; it involves more aspects. What does the coffee machine's water temperature affect?

Everyone knows that the most direct effect of water temperature on extraction is reflected in efficiency. The higher the water temperature, the higher the extraction efficiency, and the flavor substances in the coffee will be dissolved out more quickly; conversely, the lower the water temperature, the lower the extraction efficiency, and the dissolution rate of flavor substances will also slow down.

In addition to extraction efficiency, the coffee machine's water temperature also affects the flow rate of the coffee liquid, that is, the speed at which it flows out. Under the premise that other parameters remain the same, the higher the extraction water temperature, the slower the flow rate of the coffee liquid tends to be; the lower the water temperature, the relatively faster the flow rate.

Friends who have read Front Street's previous posts should be clear that the reason behind this is that the water temperature governs the speed of the puck's expansion and degassing. A higher water temperature allows the puck to expand faster and release the various substances hidden in the coffee grounds. The expanded puck compresses the gaps between the coffee grounds, while the released gas is wrapped into bubbles by the lipids in the coffee beans, creating resistance to the water flow. With the two combined, the coffee's flow rate changes accordingly. If this principle still seems confusing, you might as well try it yourself once. When the machine is turned on every morning, the coffee machine needs about 20 minutes to heat the boiler and produce steam. During this period, the extraction function can actually already operate, but the water temperature is low, usually only around 60°C.

So we can take this opportunity to observe what low-temperature espresso extraction looks like. It turns out that the flow rate of the coffee liquid is quite fast. This is precisely because the carbon dioxide is not released sufficiently and the puck's expansion rate is insufficient, which is why the flow rate changes.

The last factor affected by water temperature is the richness of the crema. Front Street has already mentioned earlier that water temperature affects the rate of carbon dioxide release, and carbon dioxide is precisely a key component of crema, so when other parameters remain unchanged, the higher the water temperature, the richer the extracted crema, and vice versa, the thinner it is.

The above are the various effects that different water temperatures can have during espresso extraction. So the next question is: for extracting espresso, exactly what water temperature is most suitable?

What water temperature is most suitable?

In fact, this is consistent with the view Front Street shared in the article "What Water Temperature Makes the Best Coffee": besides water temperature, grind, ratio, and time are also core parameters that determine the extraction result of a cup of coffee, so the specific water temperature to use still depends on how they are matched.

In the book The Extraction Science of Espresso, an imaginary experiment is recorded: Italian baristas are accustomed to using 85–91°C water to extract espresso, while American baristas tend to use 92–96°C water for extraction.

The key reason for this difference is that the ratios they use are different. The Italian standard is to extract 1 ounce of espresso from 7 grams of coffee grounds, while the American standard is to extract 1 ounce of espresso from 18–21 grams of coffee grounds. Because the ratio, time, and grind are all different, the water temperatures they use are naturally different as well.

But conversely, as Front Street said at the beginning, it is also possible to fix the water temperature and then adapt to this fixed water temperature by adjusting other parameters.

Usually, the initial water temperature of a coffee machine when it leaves the factory is set between 92°C and 96°C. This is a quite suitable temperature range, neither too low nor too high. As long as the coffee machine's initial water temperature falls within this range, unless there is a special extraction need, there is basically no need to change it.

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

It is worth mentioning that...

Just like with pour-over coffee, what we can set now is the water temperature in the boiler, not the actual water temperature during extraction. This is because the water passes through various pipes on its way from the boiler to the shower screen, and the final actual extraction water temperature will differ by a few degrees from the set value due to heat absorption.

Especially when espresso has not been extracted for a long time, the deviation between the water temperature and the set value will be even greater. So when the interval between two extractions is too long, it is best to run a blank shot of hot water before locking in the portafilter. This can not only help us calibrate the water temperature, but also conveniently clean the shower screen and wash away the "residue and grime" attached to it (which is actually coffee grounds).

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