Recap

• Burr size, sharpness, and alignment have measurable effects on the grind size distribution. That is why these factors are so important in brewing.
• A grinder in use creates heat, which increases the temperature of the ground coffee. In some cases this temperature can rise to as high as 100° C (212° F).
• These temperature changes affect shot time and extraction.
• The effect of temperature changes seems to relate not to metal parts expanding in the grinder, but rather to changes in the coffee itself — due to either impacts on grind size distribution or the reduced viscosity of oils.
• Temperature affects grind size distribution because the coffee becomes less brittle at higher temperatures, producing fewer fines and more boulders.
• Because of the importance of fines in espresso brewing, grinding at low temperatures and thus producing more fines may present some advantages.
• A practical approach in a typical cafe setting is to try to reduce temperature fluctuations by choosing a grinder design that actively controls temperature and by keeping the grinder clean and well maintained.

Glossary

Brittle A material that doesn’t deform when stress is applied but instead breaks or shatters.

Plastic A material that deforms (changes shape) when stress is applied. Plastic materials are less likely to shatter.

End 2.05