How to Remove Soap Residue from Plastic

Dear Home-Ec 101,

Help!  My plastic dishes are starting to taste (and smell) like soap.  I hand wash, and switched to a “moisturizing” dish soap this spring.  Since then, the taste is very very pronounced, even after I switched back to plain blue Dawn which several friends recommended as a remedy.  Is there anything I can do to save my favorite cups, and my kids’ bottles and sippy cups?  Is it time to switch to an all-natural soap?

Thanks so much!

Signed,
Soapy Sue


Heather says:

Soapy tasting plastic is a pretty common problem. Plastic is very porous -it has lots of tiny holes- and soap molecules are quite sticky. This problem is exacerbated when you use too much soap in the wash cycle.

Let’s dive back into high school chemistry for a moment -chem nerds bear with me I’m going to over-simplify again. Whenever you put something into water you have a solution made of  the solvent -in our case water- and solute -the soap and dirt. Even in perfect conditions only so much solute can be in solution at any given time. The actual amount is affected by things like the temperature of the water, the pH (acidity /alkalinity), and other solutes already in the solution.

Your tap water isn’t distilled -or pure water- it has minerals, chlorine, fluoride and who knows what else in it. These solutes mess with how much soap can be in your water at any given time. Detergent molecules are sort of chain shaped, one end loves water and the other hates it. When detergent is in water the water repelling side is attracted to anything that isn’t water and this is why it’s fantastic for washing. The soap surrounds soil particles and allows these particles to be in solution where they can be rinsed down the drain.

When you have too much soap, those water hating ends are going to be attracted to plastic and there are a lot of tiny holes for those molecules to sneak down into. Each time the plastic gets wet, some of those soap molecules are going to sneak back into solution. This is aggravating when that solution is water on the food you stored or cooked in plastic.

So how do you remove that soapy residue from plastic?

You want to do everything you can to increase the solubility to get those pesky soap molecules into your rinse water instead of your dinner.

To remove the soap currently clinging to your plastic, you want to use water that has had the pH altered to either be more acidic or more alkaline. You can do this by adding either vinegar or baking soda to some hot water and either soaking or swishing your plastic in this. If you add both you get the classic volcano science project that is fascinating to an eight year old, but not so cool when you’re the one who has to clean it up.

Bar Keepers Friend is oxalic acid and can be used as a paste to gently scrub your plastic and baking soda is a base that can accomplish the same end with a higher pH. Both of these things are safe for contact with food preparation surfaces, just rinse thoroughly.

If you’re still having problems there is a pretty much fail-safe way to remove soap residue from plastic. Home brewers should be quite familiar with this product PBW or Powdered Brewery Wash. You should be able to find it at a home brewing supply store or order it online. (I haven’t ordered home brewing supplies before, so I don’t have a recommended source). This product is completely safe for food and is designed to rid brewing supplies of any residues that may contaminate a batch.

To prevent soapy residue on plastic:

Do not soak plastic items, do not use too much soap, and rinse quickly and thoroughly in very hot water.

Or switch to glass for storage and reheating, here’s the set I use and love¹.

Submit your questions to helpme@home-ec101.com.

¹affiliate link

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Comments

  1. KeterMagick says

    I would take this porosity as a sign that the plastic is breaking down and needs to be replaced, as old, porous plastic leaches more compounds like BPA into the contents than newer plastic (now some are BPA free). I recently replaced my plastic storage containers with a mix of glass, some from Ikea and some from Costco, and a new plastic set from Ikea. (The Ikea set was only $4, and it is surprisingly nice.) All of my old containers were repurposed to storing small parts in the garage.

  2. Paige says

    I have found that even brand new camelbak products and plastic blender bottles, etc, are still subject to this issue, even after just one wash. Doesn’t have to be old to be worse, just depends on your water and your polymer.

  3. Tamra says

    I just bought brand new dishes from ikea and they still left reside after one wash. I soaked them in vinegar and there was no difference. Any other suggestion???