Food Containers: Stains, Smells and Warping

Plastic food containers fail in three predictable ways: they go orange, they hold smells, and they warp until the lid no longer seals. All three are consequences of what plastic is, and two of them are largely preventable.

The orange stain

Tomato-based food stains plastic because lycopene, the pigment in tomatoes, is fat-soluble — and so is polypropylene, the plastic most containers are made from. The pigment dissolves into the surface layer of the plastic rather than sitting on it, which is why scrubbing does nothing.

What removes it

• Sunlight. The most effective and the cheapest. Wash the container, then leave it outside in direct sun for a day, ideally still damp. UV breaks down the pigment. Two days clears most staining and it costs nothing.
• Bicarbonate paste. Coat the interior, leave a few hours, scrub gently with a soft brush.
• Dilute bleach soak. One tablespoon per litre, one hour, then wash and rinse thoroughly. Effective and the most aggressive option.

What prevents it

Spray the inside with cooking oil spray before adding tomato-based food. The oil film occupies the surface the pigment would otherwise dissolve into. It works remarkably well and almost nobody does it.

Failing that, use glass for anything with tomato in it.

Smells that will not wash out

Same mechanism, different molecules — odour compounds from garlic, curry, fish and onion are also fat-soluble and absorb into the plastic.

1. Bicarbonate solution soak — two tablespoons per litre of warm water, overnight.
2. Crumpled newspaper sealed inside for a few days absorbs a surprising amount.
3. White vinegar soak, one hour, then wash.
4. Sunlight again, which helps with odour as well as staining.

A container that still smells after all of that has absorbed too much to recover. Demote it to non-food storage.

Warping

Warping is heat damage, and it is what eventually kills the seal.

• The dishwasher’s bottom rack is the main culprit. The heating element sits below it and radiant heat there far exceeds the water temperature. Plastics belong on the top rack, always.
• Microwaving fatty food creates local hotspots well above the temperature of the food overall. Fat reaches far higher temperatures than water.
• Stacking hot containers before they cool deforms the ones underneath.

Once a lid or rim has warped, the seal is gone and no amount of pressing will restore it. That is the end of the container’s useful life.

Reading the plastic

Code	Plastic	Notes
5 — PP	Polypropylene	The standard for food containers. Microwave-safe, reasonably heat-tolerant
2 — HDPE	High-density polyethylene	Tough, not for microwaving
4 — LDPE	Low-density polyethylene	Flexible lids and bags
1 — PET	Polyethylene terephthalate	Single-use bottles. Not for reuse or heat
7 — Other	Mixed	Unknown composition — check the manufacturer

“Microwave-safe” means the container will not deform or leach at microwave temperatures. It does not mean the food heats evenly, and it does not cover fatty foods that create hotspots. When reheating anything oily, use glass or ceramic.

Lids, seals and stacking

• Store lids off, or ajar. A sealed damp container grows a musty smell within days.
• Silicone gasket lids — pull the gasket out and wash separately. The channel under it holds a black film and is the source of most container smells people cannot locate.
• Dry completely before stacking.
• Buy one system, not five. Containers that nest and share a lid size take a fraction of the cupboard space, and you stop losing lids.

Common questions

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