Razor Tool Guide: Trimming Your Puck for Perfect Headspace

The Breville razor dose trimming tool is one of the most underutilized accessories included with your Barista Express. This simple device solves a critical problem: creating consistent headspace between your coffee puck and the shower screen.

If you’ve been skipping the razor tool, you might be missing out on more consistent extractions. Here’s everything you need to know about using it properly.

What is the Razor Tool?

The razor tool is a flat plastic implement with a precise depth setting. When slid across your portafilter after tamping, it trims any coffee that rises above the optimal level—creating perfect headspace every time.

Think of it as a “leveling” tool for your dose. Coffee over the line gets removed; coffee below stays put.

Why Headspace Matters

The Physics of Extraction

When water enters the group head, it first hits the shower screen, then spreads across the headspace before contacting your coffee puck. This small gap (2-3mm) allows:

1. Even water distribution across the entire puck surface
2. Proper pressure buildup before extraction begins
3. Clean top surface for consistent flow

Problems Without Headspace

When your puck touches the shower screen:

• Water channels through specific points
• Extraction becomes uneven
• The top of your puck gets disturbed
• Spent puck sticks to the shower screen

Step-by-Step: Using the Razor Tool

Step 1: Dose Your Coffee

Weigh your dose as usual (18-20g depending on basket). Grind directly into the portafilter.

Tip: It’s okay to slightly overdose when using the razor tool—excess will be trimmed away.

Step 2: Distribute Grounds

Before tamping or using the razor, distribute your grounds evenly:

• Tap the sides of the portafilter
• Use a WDT tool to break clumps
• Make sure the surface is roughly level

Step 3: Light Tamp (Optional)

Some users do a light pre-tamp before razoring. This helps:

• Set the grounds in place
• Prevent the razor from dragging coffee
• Create a more defined trim line

Not everyone does this step—experiment to see what works for you.

Step 4: Position the Razor Tool

1. Place the razor on top of the portafilter rim
2. Ensure it’s sitting flat on the metal edge
3. The trimming blade should be at the correct depth

Step 5: Sweep Across

1. In one smooth motion, slide the razor across the portafilter
2. Move from one side to the other
3. Excess coffee will collect on top of the tool

Step 6: Remove and Discard Trimmed Coffee

1. Carefully lift the razor tool
2. Knock the trimmed coffee into your knock box or trash
3. Avoid letting trimmings fall back into the basket

Step 7: Final Tamp

After trimming:

1. Apply your full tamp with even pressure
2. You should see a clean, flat surface
3. Check for consistent headspace from the basket rim

When to Use the Razor Tool

Always Use It When:

• You’re learning and your doses vary day-to-day
• Using the stock Breville grinder which can produce inconsistent volumes
• Following recipes that require specific headspace
• Troubleshooting channeling or uneven extraction

You Might Skip It When:

• Your dose is already accurate and you use a scale
• Using a precision basket with known capacity
• You’ve developed consistent dosing habits

Many experienced baristas stop using the razor tool once they consistently dose exactly what their basket needs. But it remains valuable for troubleshooting or when changing beans.

Benefits of Using the Razor Tool

1. Consistent Headspace

No more guessing if your puck is too high. The razor ensures identical headspace every shot.

2. Prevents Channeling

Pucks that touch the shower screen often channel. Proper headspace eliminates this risk.

3. Safer Dosing Range

You can dose slightly higher without worrying about overdosing—excess gets trimmed.

4. Cleaner Shower Screen

Without puck contact, your shower screen stays cleaner longer.

Troubleshooting

Razor Drags Coffee

Cause: Grounds too loose or not distributed evenly

Fix: Do a light pre-tamp before razoring, or use a distribution tool first

Razor Doesn’t Trim Anything

Cause: Under-dosing—your coffee is already below the trim line

Fix: Increase your dose until you see some trimming

Inconsistent Trim Amounts

Cause: Uneven distribution before trimming

Fix: Spend more time distributing grounds before razoring

Trimmings Fall Back Into Basket

Cause: Lifting too fast or not sweeping completely

Fix: Complete the full sweep before lifting, tip razor away from basket when removing

Frequently Asked Questions

What’s perfect headspace for a 20g basket?

About 2-3mm gap between the tamped puck surface and where the shower screen sits. With proper dosing (19-21g for a 20g basket), the razor tool automatically achieves this.

Does puck trimming replace dosing scales?

No. The razor tool corrects slight overdoses but shouldn’t replace accurate dosing. Use a scale for consistency, and use the razor as a final check.

Can I use a razor tool on any portafilter?

The razor tool must match your portafilter diameter. The included Breville razor works with 54mm portafilters only. If using a 58mm portafilter, you’d need a different tool.

How does trimming affect extraction time?

If you consistently over-dosed before, you may notice faster extraction times after using the razor (because there’s less coffee). Adjust grind slightly finer if needed.

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Related Guides:

• Dosing 101: 18g vs 20g Baskets
• Tamping Technique
• Understanding Channeling