Homemade Dish Soap: Lessons Learned

I'm on my third batch of homemade dish soap now. I'm still tweaking it, but I've learned a lot so far. The first thing I've learned is that most of the people who make up recipes for soap are full of crap. Rather than putting my chemistry degree to good use and coming up with my own recipe, I relied on the advice of others. Here, then, are the consequences of my trusting nature.

After the first batch, which was way too goopy and didn't want to come out of the bottle, I looked for other recipes. All of them suggested adding lemon juice or vinegar, because the acid "helps cut grease." With batch number two, the consistency was much better. I basically did the same thing, 1/4 cup of soap flakes and 2 cups water, only this time I added several teaspoons of lemon juice. After doing a load of dishes, I noticed that all of my glasses were covered in this greasy film, and no matter how much I scrubbed, it was still there.

It soon clicked in my brain: the lemon juice did it. Very simply, the soap I'm using is made by adding a strong base to vegetable oil. So, the equation goes something like this:

oil + base -> soap

Simple enough. But adding the acid sends the reaction in the reverse direction:

soap + acid -> oil

Duh! The oily film left behind was actually oil. The solution in the bottle even separated into two phases. So, lesson learned, don't add acid to soap. My four years behind a lab bench finally paid off!

My current batch is made from 1/2 cup of soap flakes, 2 cups water, and the zest from one tangerine. It smells absolutely lovely and leaves my dishes sparkling. The tangerine does add a bit more cost, but it's still far cheaper than a commercial dish soap. I'll continue experimenting, and post some results when I come up with an optimized recipe.