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Coffee needs temperature balance.

Since the coffee machine is equipped with PID temperature control system, there has been a frenzy of temperature control. Professionals say, "We need more accurate temperatures!" and almost all manufacturers have no objection. When we think about these changes and developments, someone may ask, "is the precise temperature control of the machine so important in such a busy bar?"

Common sense of science

Everyone who has studied chemistry knows the concept of heat balance. If you mix two different substances at different temperatures, you will eventually get a substance in between. Coffee is no exception. It is a combination of hot water and cold / hot coffee.

To calculate the heat balance, we need to know the weight, initial temperature and specific heat of each material (the energy absorbed by raising the temperature of 1 g by 1 degree Celsius).

Get data

If we want to brew 40g coffee with 20g coffee powder, we need to mix 65g of water (assuming the retention rate of the liquid is 1.2). The machine may have set a temperature standard of 93 °C (199.5F). The temperature of the coffee it produces is about 20 °C (68F).

The specific heat of water is 4.18j/g/k (Joule / g / Kelvin). Coffee is made of plant materials similar to wood, not completely dry, so I will assume a specific specific heat 1.4j/g/k.

A cup of espresso starts at a lower temperature and finishes at a higher temperature, so remember that what we want to get is the average temperature of the extraction, not the absolute temperature.

So what's the result?

86.2 °C (187F), which may be lower than you think.

What's the big deal for a busy coffee bar?

The key is the temperature of the coffee powder.

The temperature controlled by the coffee machine may be surprisingly consistent, but our coffee powder will not. Grinding produces a lot of friction heat. The absorption of these hot coffee powders changes the above equation.

The bean grinder becomes very hot, and when business is good and the machine is operating frequently, they can easily spit out 50 °C (122F) coffee powder. It is 3.8 °C higher than before.

A simple experiment shows that the temperature of coffee fluctuates by 4 °C, and our machine can be accurate to 0.1 °C. we are happy about this.

Of course, accurate machines are important because they reduce large fluctuations. But you also need to consider the temperature of the coffee powder in order to grasp the overall change. If you can use an infrared thermometer to measure coffee before and after grinding, you will find a startling difference.

But remember, the most important thing in the quality of coffee is consistency. If the coffee powder temperature remains the same (that is, your service level remains relatively consistent), then your coffee temperature can reach a higher level of consistency.

The flavor and aroma of coffee are monotonous: compared with the straight fire, the beans from the semi-hot air have a single flavor. Only a good baker can make up for this defect. Of course, a good baker needs a lot of experience and distraction.