What is the difference between filter cups made of different materials? How do specific heat capacity and thermal conductivity affect coffee brewing?

"filter cup" plays an important role in the production of hand-made coffee. It not only supports the filter paper to filter coffee, but also changes the final taste of coffee because of its design, size and material. The first two front streets have been talked about many times, so today, let's talk about the "material" of the filter cup and how it affects coffee brewing.

What is the difference between filter cups made of different materials? That must be the price ~ put aside the price, the biggest difference between different materials of filter cup is its temperature control. After all, each material has different thermal conductivity (Thermal conductivity) and specific heat capacity (Specific heat capacity).

What is thermal conductivity? To put it simply, it is the speed at which heat energy is transferred (taken away) between objects. Two objects that collide with each other will eventually have the same temperature, and the higher the thermal conductivity, the faster the temperature will agree! For example, when we touch something in life and feel its warmth or coldness, it is not because of the actual temperature of the object. But it absorbs or transfers heat from us. The higher the thermal conductivity of this object, the faster it can absorb or take away heat. We can imagine that touching a piece of metal at 100 °C and a piece of rubber at 100 °C will be hot, but surely the metal will make us feel hot faster, because its thermal conductivity will be higher. It is the same reason to apply this statement to cooking!

When brewing, we will use hot water to extract the aromatic substances from the coffee powder, and the hot water will contact the filter cup along the coffee powder. At this time, the filter cup will absorb the heat energy of the hot water because of the great temperature difference between the filter cup and the hot water. The higher the thermal conductivity of the filter cup is, the faster it absorbs the heat energy of hot water.

What is the specific heat capacity? The specific heat capacity is easy to understand, that is, the heat capacity of the object. When we want to raise an object to a certain temperature, the higher the heat capacity of the object, the more temperature it needs to raise. For example, preheating coffee cups of different materials, ceramic and metal, metal coffee cups often reach the target temperature as soon as they come into contact with heat, while ceramics must be baked for a long time to reach the target temperature. This is because they have different specific heat capacities. Secondly, the specific heat capacity also determines the heat storage capacity, the lower the specific heat capacity, the stronger the heat dissipation capacity, in other words, the worse the heat preservation capacity.

And when we understand the above two points, then we can understand how the material of the filter cup affects the extraction! When the hot water spreads from the coffee powder to the filter cup, the filter cup begins to absorb the heat of the hot water until the temperature of the filter cup itself is consistent with that of the hot water, which mainly depends on the thermal conductivity and specific heat capacity of the filter cup. When the heat capacity of the filter cup is higher, the more heat energy will be absorbed, on the other hand, the heat energy of hot water will decrease, which means that the extraction efficiency of hot water will also decrease, which will eventually affect the extraction. At present, the commonly used materials of filter cups on the market are: resin, glass, ceramics and metal. According to the rate of thermal conductivity, they are ranked as follows: metal > ceramic > glass > resin, and specific heat capacity is: resin > ceramic > glass > metal (which also has something to do with their volume). According to the above theory combined with this formula, we can get the characteristics of the filter cup of different materials: the heat conduction speed of the metal filter cup is fast, and the specific heat capacity is not high, so even if it is cooked without preheating, it will not take away too much heat energy, that is, it will not affect the extraction efficiency of hot water too much; but if it is preheated, it will dissipate quickly due to the fast heat dissipation. Therefore, if you need to preheat it, you should put it into cooking as soon as possible after preheating.

The heat conduction rate of ceramic filter cup is also relatively fast, but because of its high specific heat capacity, it will absorb a large amount of heat energy of hot water without preheating, reducing the extraction efficiency of hot water and making the whole extraction different. However, if it is fully preheated before cooking, it will have a good heat preservation effect in the whole process because of the slow heat dissipation, so that the whole cooking has a higher extraction efficiency. Of course, this can easily lead to over-extraction of coffee.

On the other hand, the glass filter cup has little effect on the extraction efficiency of hot water because of its slow thermal conductivity and low heat capacity.

The resin filter cup is quite special! Although it has a high heat capacity, it does not affect the water temperature too much because it absorbs heat very slowly. Even if there is no preheating, it will not have much effect on the temperature of the water used for extraction.

So from the above we can know how the filter cups of various materials affect the cooking. Qianjie would also like to remind you that even if they are all V60 (or other filter cups), the design of the filter cups is not exactly the same due to the different manufacturing processes used by different materials.

For example: all V60, metal V60 will be faster than ceramic V60, ceramic V60 will be faster than resin V60. This is due to different processes, resulting in their diversion bone prominence, the overall size of the filter cup has a certain difference. Therefore, we can not fully apply the online extraction formula to brew coffee, because different materials will affect the extraction efficiency in many ways.

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