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P 5.02 – Corrosion

Corrosion, often referred to as rust, has an effect opposite to that of scale buildup. In coffee equipment, corrosion is caused by the interaction of water, heat, air, and chemicals in the coffee and the chemicals we use to clean our equipment. Usually, when water is corrosive, instead of depositing scale on the surfaces of your element and boiler, it can strip away limescale and damage the metal surfaces of your brewing equipment.

Fortunately, the plastic and silicone parts of brewing machines are resistant to corrosion. However, the addition of tensile stress can introduce corrosion in materials that, left undisturbed, are normally resistant to it. This is true of high-density plastics and even stainless steel. This means it is essential that brewing equipment should not be moved or knocked when it is switched on or hot. Read here an excellent summary of the eight main forms of corrosion by Desi J. Kiss.

To protect against corrosion, the incoming water needs to be balanced such that it doesn’t have too many minerals but doesn’t have too few, either. This can be managed by monitoring the water’s Langelier saturation index (LSI). We will resist the urge to dive deep into water chemistry in this course and save that for the future. But for some helpful tips on machine safety and maintenance, check out the following links:

  • Want to keep your brew water tasty and safe from corrosion or scale? This LSI calculator for Android, Water Geek, can predict how many milligrams of scale will precipitate each month in your brew boilers and steam boilers.
  • For you non-Android users, La Marzocco has a helpful water calculator.


These apps predict how scale-forming or corrosive your water will be by interpreting your Carbonate Hardness (KH),