One reason we assert that 90-95% of coffee houses aren’t producing real espresso is that baristas at the chains and most independents don’t perform many of the steps crucial for producing real espresso.  These include:

• Grinding the beans to order
• Tamping firmly and consistently
• Shot volumes at/below two ounces (for a double shot)
• Extractions times closer to 30 seconds, rather than 20 seconds.

When we visit the Top 10% of cafes where baristas are getting these steps right, we’re surprised to find that baristas there will often omit another crucial practice:  Purging the group head (i.e. running a small amount of hot water) between shots.

Here are FOUR REASONS a barista should purge the group head before locking in the portafilter and initiating the espresso shot:

1. To Remove Spent Grounds from the Dispersion Screen. When you don’t purge, you’re using the spent grounds left over from the last customer (i.e. what’s pictured in the photo above) to make the next customer’s espresso.
2. To Heat Up the Group Head/Dispersion Screen. Temperature stability is one of the most important factors in espresso extraction. When you remove the portafilter during grinding/tamping, the group head and dispersion screen begin to cool. Purging helps offset this temperature reduction.
3. To Flush Brew Water that Has Cooled. In some machines, the pipe that runs from the water boiler to the group head is not enclosed in a saturated group head. The result is that the water in this pipe will cool during the time lag between customers and no longer be hot enough for proper espresso extraction. Purging ensures that only water at the target temperature is used to extract the espresso.
4. To Flush Brew Water that May Be Too Hot. This is particularly important if you’re working with a single-boiler machine. (Note: We favor double-boiler machines.) What you’ll find is that, during a shop’s slower period, water meant for brewing will spend too much time in the heat exchange mechanism and become too hot for proper espresso extraction. Purging ensures that only water at the target temperature is used to extract the espresso.

Want to Learn More about Espresso Extraction?  Visit the Espresso Education Section of our website.