Temperature & Pressure

Temperature & Pressure in Espresso

Temperature and pressure are the driving forces of espresso extraction. While grind size is your primary adjustment tool, understanding these variables helps you fine-tune your shots and troubleshoot problems.

Brewing Temperature

The Ideal Range

Most espresso is brewed between 90-96°C (194-205°F). Within this range:

Temperature	Character	Best For
90-92°C	Brighter, more acidic	Light roasts
93-94°C	Balanced	Medium roasts
95-96°C	Fuller body, less acidity	Dark roasts

How Temperature Affects Extraction

Higher temperature:

• Extracts faster
• Increases perceived body
• Reduces acidity
• Can bring out bitterness if too high

Lower temperature:

• Extracts slower
• Preserves bright, fruity notes
• Increases perceived acidity
• May cause sourness if too low

Roast-Specific Recommendations

Light Roasts (for espresso):

• Use higher temperatures (94-96°C)
• Light roasts are denser, need more heat
• Helps develop sweetness, reduces sourness

Medium Roasts:

• Standard temperature (93-94°C)
• Most forgiving range
• Good starting point for any coffee

Dark Roasts:

• Use lower temperatures (90-92°C)
• Already more soluble, extract easier
• Lower temp prevents burnt, ashy notes

Temperature Stability

Why Stability Matters

Temperature fluctuations during a shot cause uneven extraction:

• Hotter moments extract more
• Cooler moments extract less
• Result: muddy, inconsistent flavor

Machine Types and Stability

Single Boiler (Thermoblock):

• Temperature swings between heating cycles
• Use "temperature surfing" technique
• Wait for consistent ready signal

Single Boiler (Traditional):

• Heats water and steam from same boiler
• Must wait between steaming and brewing
• Good stability once settled

Heat Exchanger (HX):

• Continuous water heating
• May need cooling flush
• "Flash" if running too hot

Dual Boiler:

• Separate brew and steam boilers
• Best temperature stability
• PID control for precision

Temperature Surfing (Single Boiler)

For machines without PID control:

1. Watch the heating light/cycle
2. Flush a small amount when heating element turns OFF
3. Wait 2-3 seconds for temperature to stabilize
4. Pull shot immediately

This catches the machine at optimal temperature.

Cooling Flush (Heat Exchanger)

HX machines can run hot if idle:

1. Idle time > 10 minutes: Flush 3-4 seconds
2. Idle time 5-10 minutes: Flush 2 seconds
3. Back-to-back shots: Usually no flush needed
4. Check your machine's manual for specific guidance

Brewing Pressure

Standard Espresso Pressure

The industry standard is 9 bars (130 psi) at the group head. This pressure:

• Forces water through finely ground coffee
• Creates the emulsion that forms crema
• Extracts oils and dissolved solids efficiently

Understanding Pressure Readings

Pump pressure vs. Brew pressure:

• Pump may show higher (10-15 bar)
• Actual brew pressure at puck is what matters
• Resistance from coffee creates "backpressure"

What the gauge tells you:

Gauge Reading	What's Happening
Below 8 bar	Grind too coarse or channeling
8-10 bar	Normal range
Above 10 bar	Grind too fine or dose too high
Climbing slowly	Possible channeling starting

Pressure Profiling

Advanced technique varying pressure during extraction:

Pre-infusion (0-2 bar):

• Low pressure water saturates puck
• Allows even wetting
• Reduces channeling risk
• Duration: 3-10 seconds

Ramp-up:

• Gradual increase to full pressure
• Gentler than instant 9 bar
• Better puck stability

Peak Pressure (8-9 bar):

• Main extraction phase
• Highest flow rate
• Most flavor extraction

Declining Pressure:

• Pressure drops toward end of shot
• Gentler extraction of late compounds
• Reduces harsh bitterness
• Mimics lever machine profiles

Pressure Profile Examples

Flat Profile (standard):

[Pre-infusion] → [9 bar constant] → [Stop]

• Most machines do this automatically
• Simple and effective

Declining Profile:

[Pre-infusion] → [9 bar] → [gradual drop to 6 bar] → [Stop]

• Reduces harsh late extraction
• Good for medium-dark roasts

Blooming Profile:

[Pre-infusion 30s] → [9 bar short] → [Stop]

• Extended pre-infusion
• Good for light roasts
• Improves evenness

Machine-Specific Considerations

Entry-Level Machines

Typical issues:

• Limited temperature control
• Pressure may not reach 9 bar
• Thermoblock temperature swings

Optimization tips:

• Let machine warm up fully (15-20 min)
• Temperature surf if applicable
• Accept some limitations, focus on grind

Prosumer Machines

Features to use:

• PID temperature control—set and forget
• Pressure gauge—monitor for consistency
• Pre-infusion if available

Optimization tips:

• Calibrate PID to actual water temperature
• Log settings that work for each coffee
• Consider adding a group thermometer

Commercial Machines

Advantages:

• Multiple group heads
• Superior stability
• Built for volume

Optimization tips:

• Regular maintenance is critical
• Group heads may vary—test each
• Clean solenoids prevent pressure issues

Troubleshooting Temperature & Pressure Issues

Shots Running Too Fast

Temperature-related causes:

• Water too hot (increases extraction rate)
• Check for scale on heating element

Pressure-related causes:

• Pump pressure dropping (wear)
• Check pump and OPV

Shots Running Too Slow

Temperature-related causes:

• Water too cold (puck becomes more resistant)
• Insufficient warmup time

Pressure-related causes:

• Pressure too high (grinder compensating?)
• Check OPV setting

Inconsistent Shots

Temperature causes:

• Fluctuating boiler temperature
• Insufficient stabilization between shots
• Thermosyphon stalling (HX machines)

Pressure causes:

• Worn pump
• Fluctuating line voltage
• Scale in system

Measuring Temperature

At the Group Head

Most accurate reading:

• Use a group thermometer
• Or measure water into cup pre-shot
• Scace device for precise testing

In the Cup

Less accurate but useful:

• Shot temperature drops ~10°C from brew temp
• A 93°C brew yields ~80-85°C in cup
• Some prefer hotter, some cooler—personal preference

Summary

Temperature and pressure are the engine of espresso extraction:

1. Start with standard settings (93°C, 9 bar)
2. Adjust temperature for roast level (lighter = hotter)
3. Ensure stability through proper warmup and technique
4. Monitor pressure as an indicator of grind and puck prep
5. Experiment with profiles if your machine allows

Master these variables alongside grind size, and you'll have complete control over your espresso.