Grinding of espresso beans

A cup of espresso requires 7 to 9 grams of ground coffee beans mixed with about 57 grams (4 tablespoons) of water. This will make a small cup of black espresso of about 43 grams, with a strong aroma, a slight bitterness in sweetness, and almost pulpy. After grinding, the oil in the coffee bean comes into contact with the air and begins to oxidize almost immediately and lose its original flavor. This will also have an impact on the bubble. To ensure the best flavor and aroma, the amount of grinding should be as close as possible to the amount needed for brewing.

Espresso powder is more delicate than the coffee powder commonly used in brewing. It is a powder-like substance with a slightly gravelly feel and similar to the density of ultra-fine granulated sugar. This density can play an appropriate role in resisting the forced flow of water. It is generally believed that the coffee powder produced by the blade grinder (that is, the blade starts to rotate after pressing the button) is of poor quality because they chop up the coffee beans and then crush them, rather than grinding them. The burr grinder is better. No matter it is hand crank type or electric type, the burr grinder can cut the coffee beans into controllable size fragments to achieve the best effect of flavor extraction.

Coffee beans (left) and coffee powder (right). These coffee beans are very finely ground and are much finer than the coffee powder used in the drip coffee machine. Please note that this density is almost like sugar.

After measuring or matching the appropriate amount of coffee powder, carefully put the powder into Gupa, a metal cup with a small hole in the bottom. Then, the compacted powder has a uniform adsorption force between the particles. Only by compacting them, the water will not flow through the powder too quickly, causing the coffee to taste too light. There are many kinds of compaction tools available. Most people like to use the flat bottom, but some people like to use the round bottom. Like many other parts of the art of making espresso, there are best standards for tightness; not too hard, not too soft, just right. Finally, the key to proper grinding is the extraction time. After the correct dose and proper compaction, the best extraction time for a small cup of espresso should be 25-30 seconds.