On the Development of a Method for Dish Sanitization

Sorry for the super late post – I was on vacation. My best friends were getting married and I wanted to devote my full attention to them. I’ll try and post again soon to make up for the wait.

I would cry if this was my kitchen...

Thank goodness this isn’t my kitchen!

By now, if you’ve been cooking along with me, your sink is full of dishes.  Probably stacked to the ceiling.  No one likes doing the dishes, least of all me, but I got to thinking: How does dish soap clean my dishes?  Does it really get my dishes that much cleaner?  Does it just remove food and grease?  Does it kill germs?!  To understand how the dishes get clean, it’s important to understand just what makes up water, what makes up the “dirty” part of dirty dishes, and how these substances interact.

There’s a saying in chemistry: Like dissolves like.  In the universe, there are two basic classes of molecules: polar molecules and non-polar molecules.  Polar substances are molecules in which the electrons are not evenly shared causing a slight charge on different ends of the molecule.  Example: water is polar, oil is non-polar.  Things like salt and sugar are polar and dissolve well in water.  Oil and water do not mix.  Like dissolves like.  You can actually demonstrate this at home!  Here’s how:

Mixing water-oil

Water and Oil don’t mix without something else. Sorry for the blue color – that’s the color of my dish soap.

  1. Take a small amount of water and a small amount of vegetable oil and pour them into something you can easily see through.
  2. Try and mix the oil and the water.  The oil and the water will un-mix on their own when you stop mixing.
  3. Add a few drops of dish soap to the oil/water mix.  Remix the oil and the water; a uniform solution will hold.
soap micelle

Amphiphilic molecules in soap surround the oil and orient them so the water-loving ends are pointed out towards the water.

To explain this, we need to add three more words.  Oil is hydrophobic, or water-fearing, while water is hydrophilic, water loving.  Because saying ‘water’ is ‘water-loving’ sounds ridiculous, also consider that you could do this same experiment with bourbon (which mixes well with water, depending on who you ask).  When you mix the water and the oil, they repel each other and separate into their respective layers.  When you add the dish soap, you add molecules that are half-hydrophobic and half-hydrophilic; scientists named these molecules amphiphilic.  Amphiphilic comes from the same root-word as “amphibian” – just as amphibians live on land and in the water, amphiphilic molecules like water and oil.  Soap contains amphiphilic molecules.

The soap molecules surround the hydrophobic oil and protect it from the water by aligning their hydrophilic heads out of the sphere.  This sphere is surrounded by water.  Voila – you’ve mixed oil and water.

The same effect is seen when you wash your dishes – non-polar, hydrophobic molecules from foods coat your dishes and the soap surrounds them so you can wash everything down the drain.  When you put a little soap on your sponge and scrub, you cause the oils to become trapped; rinse, wash, repeat.

Dish Soap Brand X

A list of ingredients in a brand of dish soap including their “use” in the product.

I don’t have a dishwasher (it’s a phase I hope to grow out of), so I often wonder if my dishes are getting as clean as I’d like them.  Let’s face it – my mouth is home to tens-of-tens-of-thousands of bacteria.  Does standard dish soap kill germs?  Turns out, most brands of dish soap (and hand soap) have a compound called triclosan (Tri like in tricycle, clo like in close, and san like in sanitation) in them.  In small doses, it prevents germs from multiplying.  In larger doses, it kills germs.  Sweet, right?  The soap above doesn’t feature a specific antibacterial ingredient and simply lists “preservative” – that said, depending on how much sodium chloride is in the soap, it may not be convenient as a food for bacteria to begin with.

Washing dishes is the worst part of cooking, for sure.  Now we know what’s happening though, which makes it a little more bearable.



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