I always have a difficult time washing greasy plastic lunchbox. I wonder if it is because some chemical or physical reaction between the container and the oil?

  • 1
    (N.B. American readers will know the objects better as "food storage containers" or "Tupperware".)
    – Sneftel
    Apr 14 '20 at 6:42
  • I think this is a duplicate of cooking.stackexchange.com/questions/95177/…
    – dbmag9
    Apr 14 '20 at 8:15
  • 1
    Does this answer your question? Why does plastic never dry properly in a dishwasher?
    – dbmag9
    Apr 14 '20 at 8:15
  • This is also important for whipping egg whites -- because there's a chance of there being grease on the bowl, they just won't whip well in a plastic bowl. Always use glass, metal, or something else that isn't plastic. (although, I've never tried wood for that)
    – Joe
    Apr 14 '20 at 13:30
  • I've never heard of a glass lunchbox. That seems very dangerous.
    – RonJohn
    Apr 14 '20 at 16:02

There are few reasons why this happens.

  1. Plastic get dull much faster than glass. Just one wash with sponge make the difference. Making more surface oil can stick to and harder for detergents to go in grooves and wash it away.
  2. Oil reacts with plastic as both are (In very very layman terms) the same. Plastic is made from oil. So when you have warm (or even hot) oil put into container (or warmed up in that container for example in microwave) you start reaction called polymerisation. The same that you use to create non-stick surface on cast iron pans.
    But here the bonds from oil bond to plastic. So you make the plastic surface oily and non-stick forever. The better quality containers have this process made during production so the polymers will "fall off".

To avoid this:

  • Don't put hot food in plastic container.
  • Don't heat up food in plastic containers. Especially ones that have dying agents (famous "tupperware after one turmeric")
  • Don't wash them with rough sponge. Usually a little bit of dish soap and hand is enough. Dishwasher might be safe from temperature point but the container is moving in the rack.
  • Some restaurants will give you a side of sauce or dip in a little plastic cup, the kind meant for takeout - which is fine for cold stuff, but I once was served queso in one of those, which was hot enough that the cup was clearly starting to melt. I sent it back and never ate there again. They're lucky I'm not a health inspector. Apr 14 '20 at 16:41

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