Descaling Your Coffee Machine: When, Why, and How

Limescale is the silent threat to coffee machines. While you can see coffee residue and milk buildup, mineral deposits form invisibly inside your machine's water pathways, accumulating slowly until they cause problems. Regular descaling removes these deposits before they affect performance or cause damage. This guide explains what scale is, why it matters, and how to descale your machine safely and effectively.

What Is Limescale?

Limescale—also called mineral scale or calcium deposits—forms when water containing dissolved minerals is heated. As water evaporates or reaches high temperatures, calcium carbonate and other minerals precipitate out of solution and deposit on surfaces. These white, chalky deposits build up over time on any surface exposed to heated water: boilers, heating elements, water lines, valves, and flow restrictors.

The amount of scale your machine develops depends on your water hardness. Hard water, common in cities like Adelaide and Perth, contains high concentrations of calcium and magnesium. Soft water, like Melbourne's mountain-sourced supply, contains fewer minerals and produces less scale. But even soft water causes some buildup over time.

Why Descaling Matters

Scale buildup causes multiple problems:

Reduced Heating Efficiency

Scale acts as an insulator. When it coats heating elements, they must work harder to heat water, consuming more energy and putting stress on components. Over time, this accelerates wear and can cause premature failure.

Temperature Instability

Espresso extraction requires precise temperature control—typically 92-96°C. Scale interferes with heat transfer, making temperature less stable and consistent. You may notice shots tasting different without changing anything else.

Restricted Water Flow

Scale narrows water passages. In severe cases, it can completely block small orifices like jet restrictors and valves. Early signs include slower brewing, reduced steam pressure, and the pump working harder than usual.

Component Damage

Left unchecked, scale can damage expensive components. Heating elements can overheat when insulated by scale, leading to failure. Boilers can develop leaks. Valves can stick. These repairs often cost hundreds of dollars.

Taste Impact

Mineral deposits can affect water chemistry and impart off-flavours. Scale can also trap coffee oils and residue, contributing to stale tastes.

How Often to Descale

Descaling frequency depends on water hardness and usage:

• Soft water (Melbourne, Hobart): Every 3-6 months
• Moderate hardness (Sydney, Brisbane): Every 2-3 months
• Hard water (Adelaide, Perth, regional areas): Monthly or more frequently

Many modern machines have scale indicators or built-in reminders based on water volume. These are helpful but may not account for your specific water hardness. If you're in a hard water area, consider descaling more frequently than the machine suggests.

Some users filter their water to reduce mineral content. While this extends the interval between descaling, it doesn't eliminate the need entirely. Filters don't remove all minerals, and some mineral content is actually desirable for coffee flavour.

Choosing a Descaling Solution

Several options exist for descaling:

Commercial Descalers

Products specifically formulated for coffee machines are the safest choice. Brands like Durgol, Dezcal, and manufacturer-specific solutions are effective and designed to be safe for your machine's materials. Follow concentration instructions carefully—stronger isn't better.

Citric Acid

Food-grade citric acid is an effective and economical alternative. Mix approximately 1-2 tablespoons per litre of water. It's gentler than some commercial products and leaves minimal residue. Citric acid is also environmentally friendly.

Vinegar (Not Recommended)

Despite common advice, vinegar is not ideal for coffee machines. Its acetic acid can damage rubber seals and gaskets over time. The strong smell is difficult to fully rinse away, potentially affecting coffee taste for multiple brews afterward. Use purpose-made descalers instead.

How to Descale: General Process

Specific procedures vary by machine, so always consult your manual. However, most descaling follows this general pattern:

Step 1: Prepare the Solution

Empty the water reservoir and fill it with descaling solution mixed to the correct concentration. For citric acid, 1-2 tablespoons per litre works well.

Step 2: Run Solution Through the Brew Circuit

Run the solution through the group head as if making coffee. Do this in cycles: run for 10-20 seconds, pause for a minute to let the solution work, then run again. Repeat until you've used about half the solution through the brew circuit.

Step 3: Address the Steam Circuit

Many machines have separate water paths for brewing and steam. Run some solution through the steam wand as well. Open the steam valve and let solution flow through. Be careful—steam may still be produced.

Step 4: Let It Soak

For heavily scaled machines, let the solution sit in the boiler and lines for 15-30 minutes. This gives the acid time to dissolve stubborn deposits.

Step 5: Rinse Thoroughly

This is critical. Empty the reservoir, fill with fresh water, and run multiple tank-fulls through both the brew and steam circuits. Any descaler residue affects coffee taste and may be harmful. Most manufacturers recommend at least two full tanks of rinse water.

Step 6: Test

Pull a shot of espresso and taste it. If there's any chemical or off-taste, rinse more. Only resume normal use when water runs completely neutral.

Special Considerations

Machines with Automatic Descaling

Many super-automatic machines have built-in descaling programs. These guide you through the process with prompts and handle timing automatically. Follow the prompts exactly—they're designed for your specific machine's water circuits.

Dual Boiler Machines

Prosumer machines with separate brew and steam boilers may require descaling each boiler independently. Consult your manual for the correct procedure. Some dual boilers have specific descaling modes.

E61 Group Heads

The classic E61 group head has an internal thermosyphon circuit that can accumulate scale. During descaling, let solution sit in the group head (without the portafilter) to address this area.

Prevention Strategies

While descaling is unavoidable, you can reduce how often it's needed:

Water Filtration

Use a water filter or filtered water to reduce mineral content. In-tank filters designed for coffee machines are convenient. External filters or filtered jugs also work. This doesn't eliminate scale but significantly slows accumulation.

Water Softening

For very hard water areas, consider a water softening solution. Some in-tank filters have softening capabilities. Whole-house softeners also help, though they add sodium to water.

Use Appropriate Water

Avoid distilled or reverse osmosis water without remineralisation—these can actually damage some machines and don't produce good coffee. Aim for filtered water with moderate mineral content: enough for good flavour and machine compatibility, not so much that scale accumulates rapidly.

The Cost of Neglect

A bottle of descaler costs $10-20. A new heating element costs $100-300 plus labour. A new boiler can exceed $500. The math is simple: regular descaling is far cheaper than repairs. If you're reading this and realise you've never descaled your years-old machine, do it soon—ideally with a commercial descaler and extra patience for soaking and rinsing.

Machines neglected for years may have scale too severe for home descaling. If water flow is severely restricted or components already damaged, professional service may be required. Technicians have stronger descaling agents and can mechanically remove stubborn deposits that acid alone won't dissolve.

Making It Routine

Add descaling to your calendar at intervals appropriate for your water hardness. Keeping descaler on hand removes the excuse of not having supplies. Making descaling routine—like changing car oil—protects your investment and ensures your machine delivers years of reliable service.

Your coffee machine works hard to bring you daily enjoyment. Regular descaling is how you return the favour, keeping internal components clean and functioning as designed. A few minutes of maintenance every month or two protects years of excellent coffee.