Physics in coffee

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One Saturday afternoon. You have just eaten the mythical paella on Sundays and you pick up the table, but you feel that you are missing something. You go to the kitchen, open the furniture on top of the stove and pick up your Italian coffee maker, that metallic gray aluminum coffee machine that was given to you when you became independent and that makes that delicious coffee. Fill the filter with coffee, the coffee maker with water and place it on the fire at half power. At 5 minutes begins to warble, signal that the coffee is ready. All the water has risen to the top of the coffee machine. You already have your coffee on the desktop ready and a pleasant smell of toasted grain permeating the entire kitchen.

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But a moment, how has the water risen from the bottom to the top if there is no motor or pump inside the coffee pot?
The truth is that the mechanism by which coffee makes this type of coffee is simple and ingenious. This type of coffee makers has 2 compartments. The lower part is where the water is poured and the upper part that contains the coffee once prepared. Both compartments are connected by a narrow tube. In the middle part of the tube is the compartment to place the ground coffee.

When placing the coffee pot on the fire, the water starts to heat up and part of it goes into a gaseous state. This causes an increase in pressure. Along the tube and in the upper compartment the pressure is lower, specifically, they are at atmospheric pressure because they are open. Right now is when physics comes into play. Due to this pressure difference, the water is pushed upwards, going up the length of the tube, passing through the ground coffee container and finally coming out through the hole at the end of the tube.

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As the temperature of the water increases, the pressure increases due to the water vapor that forms in the upper compartment. When the pressure difference between the upper and lower compartment is large enough, the water rises through the tube. Therefore in these coffee makers, the infusion is carried out at temperatures very close to boiling and pressures slightly higher than atmospheric.

The pressure is not more than the force divided by a unit of the surface so what really happens is that the force that the atmosphere exerts on the surface of the coffee is less than the force that is pushing it down, so there is a force upwards. If for some reason the pressure on the top of the tube were the same as the pressure on the water below, it would not rise since the net force would be 0.

Good friends and as we see that physics is also alive in the preparation of a simple homemade coffee, not only the chemistry as in the publication of yesterday, everything around us in a simple way has an explanation that science is ah responsible to respond and make known.

For more information visit the following links

• https://www.howitworksdaily.com/how-do-moka-pots-work/
• http://www.openculture.com/2016/06/stop-motion-film-uses-a-cup-of-coffee-to-explain-key-concepts-in-physics.html
• https://diracseashore.wordpress.com/2008/09/08/everyday-physics-coffee/
• http://theconversation.com/brewing-a-great-cup-of-coffee-depends-on-chemistry-and-physics-84473

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• https://steemit.com/steemstem/@robertoromero/the-chemistry-of-the-cafe