What exactly is the coffee fat?

Standing on the basis of the aroma and flower of coffee, it is called grease.

What is Crema?

Coffee grease is a layer of coffee foam with rich taste and aroma floating on coffee. To put it simply, the high temperature and high pressure in the brewing process combines the air with the soluble fat in the coffee, and the coffee oil is produced. Some people will call this phenomenon the Guinness effect phenomenon because it has a very similar foam layer to the famous Irish black beer (stout).

An espresso with a clearly visible coffee fat requires good quality, moderately ground coffee beans and a skilled barista. Compared with hand-brewed coffee drip coffee, coffee oil gives espresso a more saturated flavor and a stronger finish.

The process of making grease:

To understand how these oils are produced, you must first understand the process of making espresso. Take a professional espresso machine as an example, use 18 to 20 grams of coffee powder and extract 35 to 40 grams of espresso at 9 atmospheric pressure (9 Bar). High temperature, high pressure, with the right coffee powder, can make a cup of espresso.

When espresso is first extracted, there will be a golden to chocolate grease on the surface; this layer of oil is inextricably linked to pressure. When the water is heated and pressurized, the soluble substances in the coffee powder layer will be extracted, and this process will emulsify the natural fat and oil in the coffee. At the same time, freshly roasted coffee beans contain carbon dioxide, which is under pressure and melted into coffee in the process of making espresso. However, when hot water flows through the coffee pressed powder and comes out of the powder bowl, it can return from nine atmospheres to the normal one. At this time, because of the pressure gap, the carbon dioxide expands, and the oil wraps the carbon dioxide, and because the oil is lighter than water, it forms the so-called grease.