There are several factors that contribute to making a great espresso, including:

Quality of the coffee beans: The quality of the coffee beans is the most important factor in making a great espresso. The beans should be fresh, high-quality, and roasted to perfection.

Grind size: The size of the grind is important because it affects the extraction time and the flavor of the espresso. The grind should be fine and consistent.

Water temperature: The water temperature should be between 195°F and 205°F (90°C to 96°C). If the water is too hot, it can burn the coffee and produce a bitter taste.

Extraction time: The ideal extraction time for a shot of espresso is between 20 and 30 seconds. If the extraction time is too short, the espresso will be weak and watery. If the extraction time is too long, the espresso will be bitter and over-extracted.

Pressure: The pressure used to extract the espresso should be between 8 and 9 bars. This helps to extract the flavor and crema from the coffee.

Crema: The crema is the layer of foam that forms on top of the espresso. A great espresso should have a thick, creamy, and consistent crema.

Serving temperature: The ideal serving temperature for an espresso is between 160°F and 170°F (71°C to 77°C). If the espresso is too hot or too cold, it can affect the flavor.

Overall, making a great espresso requires attention to detail and a commitment to quality at every step of the process.