Chemistry of Coffee

Chemistry Connections

Episode #17

Welcome to Chemistry Connections, our names are Samhita and Hana and we are your hosts for episode 17 called the chemistry behind coffee. Today we will be discussing how chemistry affects the production of coffee.

Segment 1: Introduction to Chemistry Behind Coffee

Coffee is indigenous to countries such as Ethiopia, Brazil, India, Vietnam, Mexico, Indonesia, and Sri Lanka. Coffee beans came to be through a story of an Ethiopian goat herder named Kaldi. When the goats he took care of started to wander, Kaldi found them consuming red berries they had found, Kaldi then gave these berries to a local monk to find out what it was. The local monk gave the berries to religious individuals who found themselves with more energy after consuming them. This was then used to keep people from falling asleep during evening prayer and was later found to be coffee beans. Coffee consists of beans originated from Coffea Arabica, which actually makes up 75% of the world’s production of coffee. The cultivation and trade of coffee began in the Arabian peninsula and soon started to become popular in the homes of those in the Middle East. From the Middle East, coffee spread to other countries in the 16th century to countries such as Persia, Egypt, Syria and Turkey. Flavored coffee was introduced when regular coffee was introduced in the mid 15th century. Middle Easterners would often blend coffee with different nuts and spices to enhance the flavor. Coffee is harvested in almost every tropical country within 1000 miles of the equator. Out of the 70 species of coffee that exist, only 3 are cultivated, meaning their beans are either raw, roasted, or whole for the making of coffee. During the roasting process of coffee beans, they undergo a chemical reaction introducing about 800 compounds, ⅓ of which make up aromatic compounds.

Segment 2: The Chemistry Behind Chemistry Behind Coffee

As the beans go into the roaster, there is a decrease in temperature with the reaction being endothermic, meaning it is absorbing energy and that energy is used to evaporate water. Le Chatelier's Principle is used to explain how, once a reaction is at equilibrium, it can be stressed by changing variables in which case it is no longer at equilibrium. The reaction will shift to undo the stress placed on the reaction. We can use Le Chatelier's Principle to support that considering there is a decrease in temperature as the beans go into the roaster, the tendency of the reaction will be to go towards the side where there is no heat, which is the product in this case because the reaction is endothermic, meaning the heat is located on the side of the reactants. The result of this is that the reaction will want to increase the temperature because of that disturbance to return the reaction to a state of equilibrium. The bitter taste of coffee is produced during the roasting process. Heat and atoms have the ability to change the flavor of coffee while it is roasting but the biggest player in the staling of coffee is oxygen. When a solution comes in contact with oxygen it changes the molecular structure. Oxygen pulls away electrons from the other molecules. Since there are an uneven number of electrons, the molecules become unstable. They then begin to react with other molecules around them and this is an example of an intermolecular force called covalent bonding. Covalent bonding occurs between polar molecules that share electrons unequally. It is also an example of an intermolecular force, which is a force that holds molecules together and covalent bonding is one of the stronger ones. Coffee goes stale and reduces the aroma or flavor of coffee. This process doesn’t have to happen with the air that’s being trapped in the coffee machine but it can happen with the water that’s added to the ground coffee. Also, Oxidation occurs more at a high temperature. This is relevant when talking about the staling of coffee. The reason behind the staling of coffee has to do with oxidation. Oxidation is the process by which oxygen loses electrons. The oxygen reacts with the hydrogen, so that water is created. The hydrogen ion by itself makes the coffee more acidic. When the water is first being added to ground coffee, the hydrogen reacts with the oxygen, and the pH of the coffee rises, making it less acidic. Many different acids exist in ground coffee, some of which include phosphoric acid, malic acid, and acetic acid. Acids give off their hydrogen ion in a reaction known as a hydrolysis reaction. A lower pH means a higher acidity while a higher pH means a lower acidity. The pH of the original coffee is between 5.0 and 5.4 ( so its acidic) but its acidity can drop to 4.6 if it is kept hot for 2-3 hours, which is also why it’s advised to drink coffee fresh.

Segment 3: Personal Connections

My family and I buy different kinds of coffee beans from Starbucks. My sister and I go to Starbucks at least twice a week, so I was interested in why and how different flavors are created with the explanation of chemistry. I found it interesting how different flavors of coffee were invented at the same time as regular coffee. Everytime my sister and I go to stop and shop we buy different flavored syrups and creamers to enhance the taste of our coffee. Knowing little about the coffee world, and being an avid coffee drinker, I wanted to know more about coffee beans and how they were produced to become such a staple in American households. I was surprised to learn that 75% of the world’s coffee actually comes from coffee arabia and originated in the Middle East. Along with this, it was a topic both Samhita and I were passionate about so we would both be interested in learning more about coffee, its background, and its chemical aspects. This topic is important to us because it’s something that most people consume many times every day. It’s important that people know what they are consuming. Chemistry is all about explaining how the world around us works and learning about the chemistry of coffee is one way to bring together the chemistry we have learned this year and apply it to our everyday lives.

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