What is the purpose of tamping in espresso preparation?

Tamping is a crucial step in espresso preparation that involves pressing down the coffee grounds in the portafilter to achieve a uniform density. This process is essential for ensuring an even extraction during brewing. When the coffee grounds are tamped evenly, water can flow through them uniformly, which allows for optimal extraction of flavors and oils from the coffee. This results in a rich, balanced espresso shot with desirable characteristics.

If the coffee grounds are not tamped properly, it can lead to uneven extraction, where some parts may be over-extracted (bitter) while others may be under-extracted (sour). This inconsistency can negatively affect the taste and quality of the espresso. Thus, tamping serves the specific purpose of establishing a uniform bed of coffee that enhances the overall brewing process.