Here's how long you should actually be soaking your dishes
Is soaking overnight always the best policy?
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Between the dirty dishes, the missing food, and the huge messes, many friendships and roommate arrangements have ended due to shenanigans in a shared kitchen. While I fortunately never encountered this specific issue with my roommates, I know that leaving dirty dishes soaking in the sink for many days is akin to leaving a lit match next to a powder keg.
Fortunately, there are plenty of resources online about how to deal with recalcitrant roommates, but I realized that there was less information available about the second half of that topic—how long do dishes really need to soak in the sink before you start hand-washing them? Is it really appropriate to leave them out overnight, or is your roommate just lazy? I set out to answer this question once and for all.
Why soak your dishes?
For really bad stains, the inclination is to let dishes sit for a long time because that gives the water (and any included dish soap) plenty of time to penetrate the food stain, break it down, and reduce its ability to stick to dishes or cookware. So, in theory, longer soaking times should make it easier to hand-wash the dirty dishes later, right?
To test this theory out, I made two food stains: brownie batter and tomato sauce. I applied a little bit of each stain to a stainless steel open skillet (brownie batter) and a stainless steel pot (tomato sauce), and then cooked them in the oven at 350°F for 40 minutes. Suffice to say, opening the oven after 40 minutes was a smoky prospect.
Once the dishes were out of the oven, I’d put them in a bin, dump ¼ Tbsp of Dawn liquid dish soap in each dish, and then fill the bin with the hottest possible water from our lab faucet.
I did this experiment six times; each time I let the dishes sit in the hot water for a longer period of time (1 hour, 2 hours, 3 hours, 4 hours, 6 hours, and 24 hours). After soaking, I’d take both dishes out of the bin, run some water, and scrub them with my fingers to see how much of the burnt-on stains would come off with minimal effort.
After cooking for 40 minutes, the brownie stain wasn’t ever really “burnt,” per se, more like there were just baked brownie bits attached to the skillet.
The tomato sauce stain, though, was really and truly burnt onto the stainless steel pot. Because the brownie stain never really achieved burned status, it was already relatively easy to scrub off. The real litmus test for soaking proved to be the tomato sauce stain.
Based on the results of the tomato sauce, it makes sense to let your dishes soak for a while, up to a point. After about four hours, though, the amount of effort saved by soaking the dishes any longer is greatly reduced. Here’s the progression between stain removal and soaking time.
Soaked for 1 hour
The tomato sauce stain was about 50% removed, and the brownie stain was about 70% removed.
Soaked for 2 hours
The tomato sauce stain was about 80% removed, and the brownie stain was about 80% removed.
Soaked for 3 hours
The tomato sauce stain was about 80% removed, and the brownie stain was about 80% removed (similar results to the dishes soaked for 2 hours).
Soaked for 4 hours
The tomato sauce stain was about 90% removed, and the brownie stain was about 95% removed.
Soaked for 6 hours
The tomato sauce stain was about 50% removed, and the brownie stain was about 85% removed.
Soaked for 24 hours
The tomato sauce stain was about 60% removed, and the brownie stain was about 90% removed.
While some of the variability here is doubtlessly related to the application of the stain, if the infinite soaking idea was valid, it shouldn’t have mattered—soaking the dishes for 24 hours should have made it way easier to remove the burnt tomato sauce from the stainless steel pan than it was after soaking it for three or four hours.
As you can see, it didn’t. To further test this assertion, I repeated this experiment with Correlle bowls, which are made of a type of tempered glass. The results for the bowl with burnt-on tomato sauce were much, much worse. Soaking the bowl for 24 hours barely put a dent in lifting the burnt sauce stain from the bowl.
Why is infinite soaking not effective at removing burnt food stains?
The process of burning food (in this case, the tomato sauce) actually renders the tomato sauce into carbon; in doing so, both the food stain and the pot surface get so hot that they start to meld together. The burnt remains actually start to fill in and get captured between the tiny imperfections on the surface of the metal pot, which makes it much harder to remove. At this point, you’ll need either chemical intervention (we recommend Bar Keeper’s Friend) or mechanical action (scrubbing); passive water soaking is not going to get the job done.
The same thing can happen with dishes, where repeated usage and scrubbing can eventually wear away the dish’s finish and create those same imperfections on the surface of the dish that make it susceptible to getting stuck with tough burnt food stains and discoloration.
What should I do with my dirty dishes?
Even though it’s a pain, I recommend washing your dirty dishes immediately. This will give stains less time to set in.
If you can’t wash your dishes right away, let them soak for 3 to 4 hours. Leaving them to soak overnight is fine, but as I demonstrated, don’t expect it to be any easier to remove burnt-on stains once you’re past that 3- to 4-hour mark.
When it comes to preventative measures, in cookware, this burnt food effect can be mitigated by greasing (with eggs, butter, oil, etc.) your stainless steel pots and pans when it won’t interfere with the overall recipe.
Furthermore, this burnt food phenomenon is why some people prefer non-stick or hard anodized cookware, which coats those tiny metal imperfections or makes the surface non-reactive, respectively; in either case, it’s much more difficult for food stains to bond with the pot surface.
Anyway, next time your roommate says that he or she is leaving the dishes to soak, and the dishes are still in the sink a day later, know that he or she is definitely just lazy, rather than making a calculated effort to make it easier to remove tough food stains.