Coffee machine drip tray
Warm, wet and full of spent organic matter between emptyings. It is the part of a coffee machine most likely to smell, and the least likely to be descaled.
Precautions
- Check the manufacturer's instructions
Start here
What this is, what tends to go wrong with it, and what to do about it.
Made from
What tends to go wrong
A living growth, not a stain. Killing it and removing the staining are two separate jobs, and neither addresses the moisture that caused it.
Why it is difficult: Porous and non-porous surfaces, Moisture control and recurrence, Cleaning, sanitising and disinfecting, Organic load, Surface roughness
The flat, powdery surface growth that appears on damp fabric, grout and shower curtains — and the carpet trade's procedure for it names no bleach at all.
Why it is difficult: Moisture control and recurrence, Porous and non-porous surfaces, Organic load
- Dustvia its material
Mostly textile fibres and skin, held by static as much as by gravity — which is why a dry cloth on a plastic surface makes it worse.
Why it is difficult: Static and dust, Mechanical action and abrasion, Why different surfaces get different dirt, Surface roughness
- Fingerprintsvia its material
Skin oils transferred by touch. A greasy soil rather than a dirty one, which is why water alone does not shift them and why they return immediately.
Why it is difficult: Surfactancy
- Water marksvia its material
What hard water leaves behind when it evaporates instead of being wiped away. A mineral film, not dirt, and the fix is at the drying stage.
Why it is difficult: Water hardness, Evaporative deposition
- Rustvia its material
Hydrated iron oxide from corroding iron or steel. Distinguish a surface deposit, which cleans off, from active corrosion of the item itself, which does not.
Why it is difficult: Corrosion and passivation, Why old stains are harder, Adhesion and cohesion
- Burnt-on food and carbon depositsvia its material
Food heated until it carbonised and bonded to the surface. Time and softening do the work; scouring powder does the damage.
Why it is difficult: Contact time, Carbonisation, Adhesion and cohesion, Why old stains are harder
- Greasevia its material
Fats and oils, which water alone cannot lift. Removed by surfactants, by heat, by solvents, or by alkalis that convert the fat into soap.
Why it is difficult: Why oil resists water, Emulsification
- Heat tintvia its material
The rainbow or brown bloom on stainless steel that has been heated. Not a deposit and not dirt: the metal's own surface oxide, thickened by heat.
- Limescalevia its material
A hard, chalky calcium carbonate deposit left by hard water. Dissolved by acids, essentially untouched by detergents.
Why it is difficult: Water hardness, Crystallisation, Adhesion and cohesion
- Coffee oil residue· no established method
The film inside a brewer that makes good beans taste stale. It is an oxidised oil rather than a stain, and descaling does not touch it.
Why it is difficult: Why old stains are harder, Why oil resists water
A concentrated water-soluble dye with nothing else in it. Nothing has to be emulsified or dissolved — the only question is whether the surface has taken the colour up.
Why it is difficult: Capillary absorption, Dye migration and colour bleeding
A sticky, yellow-brown tar film deposited everywhere at once. It is the reason a room smells after everything visible has been cleaned.
Why it is difficult: Adsorption of odour molecules, Solubility and polarity
Coloured by turmeric in most prepared mustards, and curcumin is a pH indicator — which is why an alkaline cleaner turns a yellow mark red.
Why it is difficult: pH indicators in stains, Fat-soluble pigments, Photodegradation, Pigment retention
The commonest cleaning problem that is not dirt. The tackiness is the plastic's own additive arriving at the surface, which is why wiping it off works for a week.
Why it is difficult: Plasticizer migration, Damage versus soiling
The science behind this: Solvent crazing, Static and dust, Solvents and polymers, Plasticizer migration, Corrosion and passivation, Water hardness
Part of Coffee machine.
In detail
The drip tray and the used-grounds container are the parts of a coffee machine whose problem is biological rather than mineral. Spent grounds are wet, warm and organic, and the tray beneath them holds standing liquid, which makes it a growth surface and the reason a machine that has been descaled carefully can still smell. Descaling does not reach them, because the descaling programme runs through the water path and these sit outside it. The nearest measured case is another appliance with the same conditions: a study of domestic washing machines found the permanently wet parts, the detergent drawer and the lower door seal, heavily contaminated with bacteria. How a particular tray comes out and whether it may go in a dishwasher is set by the machine's maker.
Related
- Coffee machine drip tray is made from Household plastics
- Coffee machine drip tray is made from Stainless steel
- Coffee machine drip tray is commonly affected by Coffee oil residue
- Coffee machine drip tray is commonly affected by Mould
- Coffee machine drip tray is commonly affected by Mildew
Sources for this page
Sources
Microorganisms (MDPI), 2021 · Scientific literature
Relied on for: That the wet detergent drawers and door seals of domestic washing machines were significantly contaminated with bacteria, which is the nearest measured case. (inferred from the source; not stated directly)