Julia Woodbury is a recent graduate of Brigham Young University. She delights in the written word and has interests in magazine writing and editing.
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Tomato sauce is oily and pigmented; plasticware is often clean and porous. Put the two together and you get a nearly unbreakable combination of two materials. The pigment of tomato sauce seems to dye the plastic so that it doesn't become a matter of scrubbing out the material so much as a need to dye back the plastic.
For newer tomato stains that are less that a week old try treating them with baking soda. Mix enough water and baking soda to create a paste. Rub a thick amount of the paste onto the stained plastic. Allow the paste to dry and then rinse it off, rubbing it again as it washes off, then run the plasticware through a regular dishwashing cycle. Repeat the process as needed. Many have found that enough use will fade the stain in plasticware. This baking soda method simply expedites the process.
For stubborn stains that are old or that won't come out you can try putting the natural bleaching effects of the sun on your side. Simply leave the plasticware outside in a sunny place for a day. The sunshine should naturally bleach out the red tomato stain. But be aware that leaving plastic out in the sun too long or too often will probably cause brittleness and cracking in the plasticware.
Other options are to soak the plasticware overnight in warm soapy water. You can also soak the plasticware in diluted bleach until the stain is gone. Be sure to rinse your plasticware thoroughly after using bleach so that no traces of it will get in your food.
In tandem with removing stains you will also want to prevent tomato sauce stains. To provide short term protection for your plasticware, spray it with oil or cooking spray before filling it with any foods containing tomato sauce. The oil or spray will make a barrier between the plastic and the tomato pigments.
Another short term solution is to dip the plastic in cold water before using it for tomato sauce. Once you have emptied the container, use cold water to rinse it before washing it in the dishwasher.
Finally, try to not leave tomato sauce in contact with your plasticware for too long. The less time the sauce is in the plasticware, the less likely it is that it will stain.