Coffee Learning: the Secret of balancing Coffee Fat and Taste

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Espresso has mellow and rich multi-level flavor, and oil is almost the most prominent feature that distinguishes espresso from drip filtration and hand-brewed coffee. this paper explains in detail the composition and structure of oil and the influence of chemical and physical changes in espresso on coffee flavor.

The composition of coffee oil

Coffee oil (Crema) is one of the most prominent features of espresso. When coffee is extracted by pressure and temperature, carbon dioxide produced by photosynthesis in coffee cells will be released, forming a layer of fine foam on the surface of coffee, which is what we call coffee oil.

Coffee, as a crop, is rich in a variety of oils, some of which are produced by photosynthesis and others by the Maillard reaction during baking. Some of these oil molecules are hydrophilic and some are hydrophobic. Hydrophobic molecules bind to carbon dioxide molecules and separate from the coffee solution, so if you filter espresso, the oil and coffee can be separated from each other.

In addition to carbon dioxide, coffee oil also contains the hydrophobic oil molecules, water molecules and some aromatic substances we just mentioned. The existence of oil increases the complexity and balance of coffee taste and effectively avoids the volatilization of odor and taste substances in coffee.

Characteristics of Coffee Oil

We can study the characteristics of coffee oil from the perspective of time. It was just mentioned that the main components of coffee oil are carbon dioxide, oil molecules and some aromatic substances. if observed with a microscope, the top structure of the oil is very similar to that of a honeycomb. These active molecules at the top are connected to each other under the action of hydrogen bonds, molecular bonds or intermolecular forces, while the molecules at the bottom exert forces on the top molecules, thus forming the surface tension of the oil.

More importantly, there are still some molecules in the oil that move freely and are not connected to other molecules. As the water evaporates, the surface tension of these unconnected parts becomes very weak. With the passage of time, water molecules will enter the coffee solution from these parts of weak tension, thus destroying the overall force balance of the oil, the oil begins to break up, and some of the odor and taste substances begin to volatilize, thus destroying the taste of coffee. It is precisely because the tension balance is destroyed that holes appear on the surface of the grease and the thickness of the grease decreases gradually.

How coffee oil affects coffee flavor

We all know that espresso can turn sour if it is kept for too long. From a chemical point of view, there are many chemicals that cause the sour taste of coffee, mainly hydroxy acid. Internal fat is one of the thousands of chemicals in coffee. After contact with water, internal fat will be hydrolyzed to form hydroxy acid, so the taste of coffee becomes sour with the passage of time, precisely because the excess internal fat is converted into hydroxy acid.

Without fat, espresso will lose the complexity of aroma and taste in a short period of time, the balance of taste will be disrupted, and the sour taste will increase.