Physics on the Dining Table: Physics in Coffee Making
on Balancing Syphon Coffee Maker and Newton’s Law of Cooling
What?
Find out how physics takes part in a balancing syphon coffee maker and how Newton’s Law of Cooling participates in cream adding.
How?
Experiment Setup:
1. Prepare a balancing syphon coffee maker (or Vienna/Belgium coffee maker) , an alcohol burner, some boiling water and ground coffee.
2. Set up the coffee maker, place the ground coffee in the glass carafe and fill boiling water into the metal canister. Light the alcohol burner to heat the water.
×Experiments demonstration
Why?
1. Why can the boiling water flow from the metal canister to the glass jar?
2. Why does the alcohol burner cap drop and put out the fire?
3. When the fire goes out, why can the coffee flow back to the metal canister?
4. Why doesn’t the coffee flow out when the spigot is turned on?
5. Prepare two cups of coffee with the same temperature. Add cream to one cup immediately while to the other few minutes later. Measure and compare the temperature difference of the two cups.
×Think...
1. The water-filled metal canister becomes an airtight chamber when the plug is screwed on. Inside the chamber, water is heated by the alcohol burner and is gradually transformed into steam and pressurizes the chamber. As the water temperature reaches 100 ℃ and changes a mass amount of water into steam, the chamber pressure becomes higher than one atmospheric pressure and thus pushes the boiling water to the glass jar.
2. The frame of the coffee maker functions as a lever balance that carries the metal canister at one arm. Firstly the canister gains weight from the water filled inside and tilts the balance lever. When the water boils and flows to the glass jar, the canister is tipped from the weight loss and releases the burner’s cap it originally props up.
3. When the fire goes out, the temperature of the canister drops gradually. The steam inside the canister is thus condensed and makes the chamber pressure lower than one atmospheric pressure. The finished coffee is therefore sucked back into the canister owing to the pressure difference.
4. When the finished coffee flows back, the pressure inside the chamber is still slightly lower than the ambient atmospheric pressure and withholds the coffee from flowing out of the spigot. After screwing off the plug, having the chamber pressure balanced with the atmospheric pressure, the coffee is allowed to flow out when the spigot is turned on.
5. Cream, whose specific heat is higher than coffee, helps to hold the temperature from dropping quickly, so the cup with cream earlier maintains a higher temperature.
Questions
- Can the phenomenon that the finished coffee flows back from the glass jar to the metal canister be explained by syphon effect?
- When the coffee is finished, if we remain the plug screwed on and leave the canister for half a day or longer, can the coffee flow out when we turn on the spigot?
About the Experiment
- The coffee maker is a commercial product.
- Compare this experiment with a syphon vacuum coffee maker.
Reference
- Robert E. (1997). When to add the cream to your coffee. Why Toast Lands Jelly-Side Down: Zen and the Art of Physics Demonstrations (pp. 113-116). West Sussex: Princeton University Press.
- Rees W. G., Viney C. (1988). On cooling tea and coffee. American Association of Physics Teachers, 56(5), 434-437.
Related Links
- Glamour of Coffee. Discover (Vol. 161). Taipei: Da-Ai TV.
Producer
Ching-Chi Chu （朱慶琪）
Advisor
Ching-Chi Chu （朱慶琪）
Written by
Chang-Han Tsai （蔡昌翰）, Shi-Lin Huang （黃時霖）
Translator
Hsiao-Ching Su （蘇筱晴）
