The Chemistry of a Latte

Introduction

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A latte is a fundamental part of every coffee shop and almost every American’s life. A latte is composed of milk and espresso, which have both been heated separately and brought together. The chemist in charge of this reaction is known as the barista, the barista can change the flavor of the coffee by his method and also the area where the coffee beans are grown.


I did the chemistry of  a latte because of its daily affect on me, and also because of the great experience I had with it this past summer. In the year 2015, I traveled the nation for two months with a coffee shop known as Off the Leaf. On this trip, I made coffee everyday, and had an excellent esperience. From this trip, I became curious as to what was in my favorite drink.


Studying coffee has made me love it even more. I still drink it daily, but now have more respect for the exquisite taste. I also understand coffee as more of an art and chemistry  now, than ever before. To make good coffee requires more effort than most people know.


Composition of ...

  • Water: H2O

  • Caffeine Molecule: C8H10N4O2

  • Galactose Molecule: C6H12O6

  • Sucrose: C12H22O11

  • Chlorogenic acids: C16H18O9

  • Lignin: C9H10O2, C10H12O3,   C11H14O4

  • Triglycerides: C55H98O6

  • Trigonelline: C7H7NO2

  • Quinic Acid: C7H12O6


Main Chemicals, Compounds, Components

Espresso

Espresso is made by ground coffee beans and water. Heated water is forced through the ground coffee beans, which have been pressed into a solid puck. The water which passes through this ground coffee, carries with it micromolecules of the coffee beans with it. On top of the espresso will normally form crema, which is composed of near 1,000 aromatic chemicals. The crema can determine the flavor of the espresso , and also the quality of the barista. The maillard reaction is an important part of this, since the molecules of the coffee are carmelized. Due to the chlorogenic acid lactones, the espresso will normally taste bitter, but it can be sweet, if the reaction is performed correctly. If the water is heated properly, the right amount of water is pushed through, and  the correct coffee is being used, the reaction between the amino acids and reducing sugars will create sweet enough molecules to overpowere the chlorogenic acid lactones,.





Milk

Milk is made up of 87% water. the remaining 13%  is composed of minerals and vitamins, such as calcium, potassium, and vitamin A. The milk needed for a latte must be heated  to a high temperature, to once again cause the maillard reaction. The milk of a latte is normally much sweeter than the espresso. This is due to the lack of chlorogenic acid in milk, and also the easier carmelized milk proteins.If heated correctly, the milk will be very sweet, and pair well with the slightly sweet and strong espresso taste.



Chemistry's Role

Both the milk, and the coffee bean are grown naturally and harvested on farms. The coffee is normally handpicked by workers once or twice a year. The picked coffee cherry is sorted by hand or machine, and only the best is kept. This sorted batch of coffee cherries is then dried, normally in the sun, and cracks to reveal the inside of the coffee cherry. The coffee is bagged, and then sent to the coffee roaster, who cleans, and heats the cherries til they are the wanted flavor and color. The coffee is bagged again, and this time sent to the coffee shop. Many coffee shops grind coffee on site.

The milk is a different process. A cow is milked by vacuum, and the milk is stored in a cooling tank. The milk is taken to a factory, where the bacteria and debris are seperated from the milk. Vitamins A and D are added to the milk, along with other minerals and vitamins. The milk is then superheated and cooled, to kill off all remaining bacteria. The milk is pressurized to homogenize it, and keep all cream off the surface. Finally, the milk is bottled and sent away.

Background Research

Coffee has been drank for centuries by the aztecs and ancient civilizations. The invention of espresso, however, was created in the early European 17th century. Originally, coffee was thought to be rank and bad tasting, but once the process of espresso was created, more people sought after it. Espresso was first enjoyed in countries such as Italy and Turkey. Almost 300 years later, millions enjoy coffee daily. The process has changed throughout the years, but the desire for caffeine has not.

Resources

http://www.chemistryviews.org/details/ezine/694285/Espresso__A_Three-Step_Preparation.html

How to make coffee


http://www.ift.org/~/media/Knowledge%20Center/Publications/Books/Samples/IFTPressBook_Coffee_PreviewChapter.pdf

Chemical components of coffee


http://coffeegeek.com/guides/frothingguide/milk

How to steam milk; lipids and fats in milk


https://scienceandfooducla.wordpress.com/2015/07/21/the-science-of-steamed-milk-understanding-your-latte-art/

Proteins in milk


http://legacy.sweetmarias.com/library/content/espresso-preparing-milk-drinks-espresso-steaming-milk

How to steam milk


http://ansci.illinois.edu/static/ansc438/Milkcompsynth/milkcomp_minerals.html

Composition of milk



https://en.wikipedia.org/wiki/Caffeine

Caffeine molecule and site


https://www.ilri.org/InfoServ/Webpub/fulldocs/ilca_manual4/Milkchemistry.htm

How milk is made


http://www.ncausa.org/About-Coffee/10-Steps-from-Seed-to-Cup

How coffee is grown and extracted


http://drinks.seriouseats.com/2014/02/how-espresso-is-made-step-by-step-barista-grind-portafilter-extraction-shot.html

More on how coffee is extracted


https://en.wikipedia.org/wiki/Maillard_reaction

maillard reaction site

About the Author
Zach Brant is a Senior at Billings Senior High who attends Varsity choir and a number of AP classes. Zach enjoys fishing, hiking, backpacking, and traveling in general. Zach hopes to go on to be an astrophysicist and change the world. He has recently spent the past summer making coffee and traveling on a summer tour. Coffee is one of the best parts of his life.
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