How does the water temperature of the coffee machine affect extraction? How are Crema and oils formed? Does grease affect the flow rate?

Qianjie often mentions Italian concentrated extraction, mostly emphasizing the parameters such as grinding, proportion, time, and pressure, and rarely mentioning the water temperature of the coffee machine! But this does not mean that the extraction water temperature of the coffee machine is not important, just because the boiler water temperature of many coffee machines can not be changed at will, so we directly regard the water temperature as a fixed value and adjust other extraction parameters to match the water temperature. so that coffee has a suitable extraction.

Water as the solvent of coffee, its temperature determines the extraction efficiency! When the temperature is higher, the extraction efficiency of water is higher, and the temperature is lower, then the extraction efficiency of water is lower! This is a well-known thing. But you know what? For the "radical" pressurized extraction, the water temperature brings not only the direct strength of the extraction efficiency, but also other aspects of influence!

Another effect of water temperature on pressurized extraction-the flow rate two days ago shared the reasons for the hardening of espresso oil, in which it was mentioned that when the extraction efficiency of the parameters is too high, it will cause a large amount of carbon dioxide to be released in a short time, thus making Crema more abundant! And this includes the temperature of the water!

In the pressurized extraction, the released carbon dioxide will be wrapped by protein and oil, forming countless bubbles, which are pressed out of pressed powder is Crema! Before it is pressed out, the bubble will become an obstacle in the process of extraction, reducing the gap in which hot water can flow, thus slowing down the flow rate. When the water temperature is not high, because the extraction efficiency becomes lower, so carbon dioxide will not be released quickly in a short time. Without the hindrance of bubbles, the faster the flow rate.

In addition, most single-ended household coffee machine boilers are relatively small, so they can store less hot water! When continuously out of the cup, we can find that the extraction flow rate of espresso is unstable. Because this is caused by the boiler's failure to heat up in time after replenishing water, it makes a difference in the flow rate of coffee extraction and the taste of coffee! This is also the biggest difference between commercial machines and household machines. Because the flow rate is also a controlling factor of extraction efficiency, the water temperature, which plays two important roles, is very important.

At what temperature should the water temperature of the coffee machine be set? Most coffee machines leave the factory with a set temperature of 92 °C, which is a very reasonable temperature. If there is no special need, we basically do not have to regulate the water temperature. Unless the roasting degree of the coffee you extract is shallow, or the grinding is not so fine, then we can raise the water temperature to make the extraction more efficient, depending on the situation. But try not to let the water temperature below 92 °C (unless there is a special need), because the temperature we see is not the extraction temperature!

Why is the temperature we see not the extraction temperature? Although we can see the temperature of the water through the thermometer of the coffee machine, in fact, this thermometer shows only the temperature of the water in the boiler, not the temperature used to extract coffee.

Hot water from the boiler to the water distribution network will pass through a section of pipes, including the water distribution network, will absorb the temperature of the hot water, resulting in a deviation between the final extraction water temperature and the displayed boiler water temperature. After a period of hot water release and preheating, the result measured again is about 82 °C.

Therefore, in order to avoid this situation, we will preheat the coffee by empty water before extraction, so that the extraction can be more stable! And this also makes us need to note that the thermometer does not show the temperature of the water used for extraction, so it is best to use it more carefully.

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