Factors affecting coffee quality: coffee requires temperature balance and data

Coffee needs temperature balance.

Since coffee machines were equipped with PID temperature control systems, there has been a wave of temperature control. Experts say: "We need more accurate temperatures!", Almost all manufacturers have no objection to this. When we think about these changes and developments, one might ask,"Is it so important to have precise temperature control of machines in such a busy bar?"

scientific common sense

Everyone who has studied chemistry knows the concept of heat equilibrium. Mix two different substances at different temperatures and you end up with something in between. Coffee is no exception, it is a combination of hot water and cold/hot coffee.

To calculate thermal equilibrium, we need to know the weight, starting temperature, and specific heat of each material (the amount of energy absorbed by a gram of matter to increase its temperature by 1 degree Celsius).

obtain data

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

The specific heat of water is 4.18j/g/k(joules/grams/kelvin). Coffee is made from plant material similar in texture to wood, not completely dry, so I will assume a specific heat of 1.4j/g/k.

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

So what's the result?

86.2°C (187F), probably lower than you think.

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

The key is the temperature of the coffee powder.

Coffee machines may control temperatures surprisingly consistently, but our coffee grounds don't. Grinding produces a lot of frictional heat. These hot coffee powders absorb and change the equation above.

Grinders can get hot, and when business is good and the machines are operating frequently, they can easily spit out coffee powder at 50°C(122F). 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, which we are happy with.

Of course, precision machines are important because they reduce large fluctuations. However, it is also necessary to consider the temperature of the coffee powder in order to grasp the overall change. If you can measure coffee before and after grinding with an infrared thermometer, you will find a surprising difference.

But remember, the most important thing about coffee quality is consistency. If the ground coffee temperature remains consistent (i.e., your service level remains relatively consistent), then your coffee temperature can achieve a higher level of consistency.

Source: Brista Blog