The Physics Behind Latte Art by Sarah Hiranandani

As I was sitting thinking about what I should write my physics news on, I was sipping a cup of coffee. This made me think about our current unit on fluids and buoyancy. I began to think about latte art and how is it that people can seemingly “draw” all kinds of pictures using steamed milk on top of a couple espresso shots already in the cup.

As we are beginning to discuss in class, the density of an object or in this case another liquid is crucial to our understanding of how it interacts with other liquids. I was perplexed by how if one were to just pour milk into a couple shots of espresso, without having frothed or steamed it first, it would simply mix with the espresso; however, if the milk is frothed or steamed first it begins to clump together in the latte and can create beautiful art as seen in the pictures above.

Milk is steamed most often in coffee shops using a steam wand that both spins the milk as well as heats it as it creates small bubbles in the milk to make more of a foamy texture. Because of this porous foam that develops, the milk begins to seemingly float on top of the espresso because it is able to “hold other liquids” in between its bubbles. Due to the foams elasticity, and ability to bounce back into shape, its able to hold these borders between the brown coffee mixture and the steamed milk. 

This is in contrast to a layered latte when lighter/less dense espresso is poured into more dense milk. As we discussed in class, a denser object and/or fluid will fall to the bottom, which creates the layered affect seen in the picture below. This contrast is directly due to the difference in density of the two liquids, and the rate at which they are poured, as well as their temperature which results in them floating or being submerged. The density of milk at 38.9 degrees celsius is 1.026 kg/L3 while the density of espresso is only 1 kg/L, and therefore is less than most milk's when steamed. So, we can use this density to our advantage and create some fun latte art or a nice layered latte.

Sources

Defining Espresso (2020), Parchmen & Co., Article: https://www.parchmen.co/blogs/writing-about-our-passion/defining-espresso#:~:text=As%20such%2C%20given%20that%20the,or%20%3E%201%20gm%2Fml

The Physics Factbook: An Encyclopedia of Scientific Essays:

https://hypertextbook.com/facts/2002/AliciaNoelleJones.shtml

Uyeno, Greg, “How does latte art work?” Live Science https://www.livescience.com/55696-how-does-latte-art-work.html

Images:

https://www.lesswastecoffee.com/barista-pen-for-latte-art.html

https://eldoradocoffee.com/blogs/news/latte-art-home