Talking about Coffee: fried Coffee Curve and Boat (part two)

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"do you know the difference between boiling water and fried coffee beans?" I use the simplest analogy to inspire colleagues to think.

Chemical reactions aside, the physical changes of coffee beans during heating are already quite complex: the same bean, fried in the same way (that is, the same roasting curve), may not taste the same. Some enthusiasts like to stick graphs on their bags when communicating. Although this helps testers understand the basic information about the baking period, it is almost impossible to copy the taste by chart alone: when learning to stir-fry beans, the author likes to try to stir-fry coffee in the same producing area with the curve recommended by others on the Internet, but the results vary, and many expected flavors do not appear. One reason is that the figures reflected by the thermometer do not represent the real situation: like hot water in a water pot, the bottom is hotter than the top. And the location of the thermometer, each brand of fried bean machine is different. Even if it is the same model, professional bakers will make adjustments before using it.

Assuming that the thermometer is accurate, it only measures the surface temperature between beans. It's like a giant oven full of chickens of different sizes. The figures on the display screen do not reflect the deepest temperature of the chicken.

Unlike boiling water, coffee beans go through two "endothermic and exothermic" (endothermic-exothermic) stages during heating: when the beans are still emerald green and have a high water content, the heat is first absorbed and evaporated by the water, and the temperature rises slowly. On the contrary, coffee beans will release heat during the first explosion (as well as the second explosion). If you don't try to lower the temperature in the furnace, you will quickly stir-fry the beans or even catch fire! Therefore, stir-frying coffee must not be like boiling water, and the firepower does not have to be changed at the beginning and before the stove is turned off.

The baking curve is S-shaped.

Some bakers will adjust their firepower by "how long it takes to rise one degree". Generally speaking, the initial heating up of fried beans is faster, but it needs to be slowed down before and after the explosion. So the normal baking curve is S-shaped. But if the firepower is increased when it is too late, the temperature in the furnace lags behind: like a ship, it takes a long time to accelerate from the engine to change the ship's inertia. Cooling is easier: when the temperature rises too fast, in addition to reducing the firepower, the baker can also use the air outlet commonly known as the "throttle" to remove hot air from the furnace for rapid cooling. The principle is like driving a sports car to "step on the oil while stepping on the brake" without reducing the engine speed but achieving the goal of deceleration. However, this method will lead to the imbalance of "conduction and convection". Even if the chart seems to be up to standard, the taste of the coffee fried by "heated by a big fire and cooled by a strong wind" is not delicate.

The small universe in the fried bean machine

Tons of coffee rotates in the drum, moving like a liquid. The state of the furnace will operate like a star in accordance with the rules laid down by the baker. Each bean, however, evolves according to its own quality and characteristics, releasing thousands of fragrances and extending in all directions at the moment of bursting. What happens in the bean machine contains a macro picture as well as a micro world: like general relativity and quantum mechanics, they are uncompromising but resonate harmoniously.

(note: the amount of heat required to heat up a certain weight of water will change due to the density and pressure of the water. By using the analogy of boiling water, the author simplifies the physical conclusion. )

Patrick Tam (owner of the boutique coffee shop Knockbox, approved barista of the American Fine Coffee Association and European Fine Coffee Association, CQI recognized cup tester, Cup of Excellence's first Hong Kong judge)