How to Remove Soap Residue from Plastic

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Dear Home-Ec 101,

My plastic dishes are starting to taste (and smell) like soap. Help!

Because I hand wash, I switched to “moisturizing” dish soap. Since the switch, the soapy taste has been overwhelming. I can still taste the soap, 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

Soapy-tasting plastic is a pretty common problem.

Plastic is very porous —it has lots of tiny holes—and soap molecules are pretty sticky. This problem is exacerbated when too much soap is in the wash cycle.

Let’s dive back into high school chemistry for a moment—chem nerds, bear with me; I’m oversimplifying again. Whenever you put something into the water, you create a solution. This solution is made of the solvent water and solute, 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. We talk about chemistry a lot in our laundry section.

Your tap water isn’t distilled—or pure water—it has minerals, chlorine, fluoride and who knows what else. These solutes mess with how much soap can be in your water at any given time.

Detergent molecules are 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, which is why it’s fantastic for washing. The detergent molecules surround soil particles and allow these particles to be in solution where they can then be rinsed down the drain.

When you have too much soap, you end up with soapy-tasting plastic.

Have you ever noticed how hard it can be to rinse oil and grease from plastic? The side of the detergent molecules that is attracted to oil is also attracted to plastic and that can make it a little difficult to rinse away, just like oil can be, it wants to cling to the plastic, especially in the tiny holes and crevices.

Each time the plastic gets wet, some of these soap molecules do sneak back into the solution and that is what you are tasting.

Your goal is to ensure that all the detergent is removed so that no soap ends up in your food or water.

How do you remove that soapy residue from plastic?

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

What increases solubility?

Increasing the temperature and changing the pH of the water used to rinse away the soap

To remove the soap currently clinging to your plastic, you want to use water that has been altered to either be more acidic or more alkaline (basic).

You can do this by adding either vinegar or baking soda to some hot water and soaking or swishing your plastic in the water. Don’t use both acidic and basic ingredients unless you want to repeat a sixth-grade science project and make bubbles and salt.

If you are trying to salvage some reusable straws, put on some gloves and get one of the straw cleaners and really go to town scrubbing with the straws immersed in the hottest water you can tolerate. Be careful and do not delegate this task to a child. It’s easy to scald yourself. Please use gloves.

There is a lot of surface area for those detergent molecules to cling to, and without scrubbing/agitation, you’re going to have a hard time removing all of them.

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

If you’re still having problems, there is a fail-safe way to remove soap residue from plastic. Homebrewers should be pretty 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. This product is completely safe for food and is designed to rid brewing supplies of residues that may contaminate a batch.

To prevent soapy residue on plastic:

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

Or switch to glass for storage and reheating Pyrex 1072164 Storage 18-Piece Round Set. Here’s the set I use and love¹.

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

¹affiliate link

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5 thoughts on “How to Remove Soap Residue from Plastic”

  1. 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.

    Reply
  2. 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.

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  3. 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???

    Reply
  4. How to get smell and taste out of Cuisinart Brew Central Coffee Maker that I mistakely CLEANED with ODOBAN instead of VINEGAR????? The inside where you POUR WATER is PLASTIC!

    Reply
    • Oh no! I checked their website and it appears that food contact surfaces should just be rinsed with water. Run a few cycles of water through and then a cycle of vinegar – like you meant to and then a couple more of plain water.
      I would not use the coffee maker until you no longer smell the vinegar.

      Reply

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