Lecture Notes: Understanding Crema in Espresso

Introduction to Crema

• Crema: The red-brown foam on top of a well-made espresso.
• Purpose of Lecture: Discuss what crema is, its origin, desirability, and impact on the taste of espresso.

Historical Background

• Origin of Term:
  • "Crema" is derived from the Italian word for cream but refers to foam.
  • Coined by Achille Gaggia with his new espresso machine in the late 1940s.
  • Marketed as "crema cafe naturale" to highlight espresso's unique characteristic.

Formation of Crema

• Roasting Process:
  • During roasting, CO2 is produced and trapped in coffee beans.
  • Fresh coffee beans contain a substantial amount of CO2.
• Brewing Process:
  • Hot water under high pressure (9 bars) in espresso machines dissolves CO2 from coffee grounds.
  • Transition from pressurized to atmospheric environment causes CO2 to form bubbles, creating crema.

Why Coffee Foams

• Foaming Explained:
  • Foam is air bubbles in a liquid stabilized by surfactants.
  • Surfactants in espresso include melanoidins and protein-derived roasting byproducts, not primarily caffeine.

Factors Affecting Crema

• Color and Appearance:

  • Tied to the extraction level and roast level of the coffee.
  • Darker roasts generally produce darker crema due to more CO2.

• Coffee Type:

  • Robusta coffee often used for more crema: More CO2 and less oil than Arabica, increasing foam stability.

• Oil Content:

  • High lipid content (from Arabica) can destabilize foam, as fats provide an alternative to air bubbles for proteins.

Skimming Crema

• Taste Impact:
  • Skimming off crema reduces bitterness and roasty notes.
  • Experimentation shows crema affects top-level aromas but not the core taste profile.

Practical Insights

• Chasing Crema:
  • More crema doesn’t necessarily improve taste.
  • Freshness and roast level influence crema quantity and color.
• Experimentation:
  • Force carbonating coffee beans doesn’t increase crema.

Conclusion

• Summary:
  • Crema is an indicator of a well-brewed espresso, but not a determinant of coffee quality.
  • More crema is not always desirable for flavor enhancement.

Additional Resources

• Further Reading: Suggested scientific papers and studies related to crema available on the presenter’s website.

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