Written by Greg Laden.

Does it save energy to pre-rinse the dishes?

As an anthropologist, I find the interface between technology and the larger culture in which it is embedded fascinating.

You all know the old story of the family cook who habitually cuts the ends off the roast before slipping it in the oven. One day her child, hoping some day to be the family cook, asks why this is done. It turns out that nobody can remember, and the matter is dropped. But the question comes up again, at a later family dinner, this one attended by great grandma, who was the family cook a generation ago, and of course, she knows the answer.

“Back in the day,” she says, “It was the depression. We weren’t able to just go to the store and buy whatever we wanted, like people these days.”

Grandma always managed to work in a mention of how poor they were back in the depression. But this time it was relevant. “We had only one roasting pan,” she continued. “It was only 14 inches long and the roast was always a few inches longer. So I’d cut the ends off.”

And of course, ever since then, subsequent generations had learned to cut off the ends of the roast because that is how grandma did it, and there must have been some reason, though nobody knew what it was. And now, the roast, be-ended, sits small in the large stainless steel double handed Williams Sonoma roasting pan.

That’s how Grandma did it, and there must have been some reason, though nobody knew what it was.

I think that is how some people load their dishwashers.

Back in the day, dishwashers weren’t very good at washing dishes. They were really status symbols that did little more than rinse off the dishes that you’d already scraped and run under the faucet. You put dishes in the dishwasher that already looked pretty clean. The role of the dishwasher was to remove the few remaining cooties (or dog saliva for some households) and, if you kept up the supply of anti-spotting juice, to make sure that the glassware was shiny-clean.

Dishwashers have changed. A reasonably good dishwasher, not even the most expensive or fancy, does a much better job at washing dishes. Even cheap ones, probably.

The difference in price between dishwashers is mostly a matter of bells and whistles and whether or not it has a stainless steel front, that sort of thing. Inside, the engineering of how to spray water on dishes from various angles for a very long period of time has been worked out.

These days, you only need to remove the large parts, the parts that remain because people these days, unlike back in the depression when there was not enough food, have forgotten that they should finish the food on their plate. Even the chicken bones. Back in the depression, people ate the chicken bones.

When you wash dishes in the sink, you use water and energy. The energy is to heat the water, but also, the water itself requires energy to process and pump. When you wash dishes in the dishwasher, you use energy. Again, heating and getting water are factors, but also, the dishwasher has a pump and may have a water heating element, and of course, a drying element. More on the drying element later.

If you did a complete hand washing job on your dishes, then ran your dishes on a full cycle in the dishwasher, you would be using way more energy and water than required to actually get the dishes clean. But if you only hand wash the dishes a little — scrape the plates than run them under the water — maybe you are using less energy and water. But the fact remains, if you just scraped the dishes minimally and the put them in the dishwasher straight away, with absolutely no rinsing, you will use a minimal amount of energy.

Some people claim that they do hand washing so efficiently that they are using less energy than a dishwasher would ever use. Such folk eschew the dishwashing machine entirely. However, dishwasher experts claim that this is only rarely the case. The dishwasher uses a small percentage of the water and energy you use in hand washing.

Don’t pre-rinse the dishes. Just put the damn things in the dishwasher

Chis Mooney has written up the current research on dishwashing efficiency. His Washington Post article cites research from the EPA, the Natural Resources Defense Council, and the American Council for an Energy Efficient Economy.

The bottom line: Don’t pre-rinse the dishes. Just put the damn dishes in the dishwasher. Oh, and you think your hand washing is efficient, do consider the possibility that you don’t really know that. You just think that because you want to. It is almost certainly the case that you can’t really prove that and it is likely (but not impossible) that it simply isn’t true. From Moony’s Washington Post article:

… dishwashers just keep needing less and less water (and energy) because of improving appliance standards, even as they get better and better at using it.

“While it may be possible to use less water/energy by washing dishes by hand, it is extremely unlikely,” Jonah Schein, technical coordinator for homes and buildings in the EPA’s WaterSense program, said…

“In order to wash the same amount of dishes that can fit in a single load of a full size dishwasher and use less water, you would need to be able to wash eight full place settings and still limit the total amount of time that the faucet was running to less than two minutes,” he said.

“…modern dishwashers can outperform all but the most frugal hand washers,” adds the American Council for an Energy-Efficient Economy.

This applies to modern Energy-Star rated dishwashers. Which, if your dishwasher is reasonably new, is probably your dishwasher. And by new, we mean up to several years old because this has been true for a long time. Moony’s story has further details on exactly what makes dishwashers more efficient.

So, this is like cutting the ends off the roast. In the old days, you needed to wash your dishes before you washed your dishes. Now, you can just wash your dishes. But do you? Or are you still cutting the ends off the roast?

(It is unfortunate for the dogs that they lose in both cases.)

Moony also talks about the drying element in dishwashers, and I have a word or two to say about that as well.

Why use the heating element at all?

Consider the term “dishwasher safe.” In my household, everything is “dishwasher safe.” This is because I put everything in the dishwasher. If something is not dishwasher safe, it gets weeded out.

Most things that are not dishwasher safe are subject to heat damage when the drying element comes on. I installed our present dishwasher about five years ago. The heating element has yet to come on. Well, it did by accident once and boy, did that smell bad. (If you don’t use the heating element, it tends to accumulate a layer of stuff that smells bad once you do turn it on). This is not to say that the only unsafe thing in a dishwasher, if you are a plate or a bowl or something, is the heating element.

The water in a dishwasher is hot, and the chemicals are caustic. We have a number of coffee mugs that no longer say what they formerly said because the cheap printing process used to make them did not stand up to the slings and arrows of outrageous technology.

Those coffee mugs that change on the outside when you put hot coffee in them? That works because of a layer of cheap plastic on the outside of the cup. My Doctor Who mug (where the Tardis disappears and reappears) lasted one day. I still have it but it is a simple black mug with no evidence that the Doctor ever existed. And, when I pop in “clean recyclables” like a peanut butter jar made of plastic, that stuff comes out distorted and half melted, but not really melted and it isn’t a problem; it was on the way to the recycling bin anyway.

If you never turn on your heating element you will use a lot less electricity and many non-dishwasher safe items survive the dishwasher. I’m not making any promises, I’m just telling you what I do. Don’t worry, the dishes get dry. Modern dishwashers run some air through after the washing is finished on a full cycle, and if you open the door, physics, in the form of evaporation, will work very well.

This, of course, is a metaphor for many other things. Consider the culture of your use of technology. Do you let your car warm up for a long time on a cold winter morning? Do you leave it running when not actually driving because you heard it takes more energy to start it than to run it for a while? Do you leave florescent lights on in the office all day even when the rooms are empty because you heard that was more efficient? As usual, you are probably doing it all wrong. Not your fault, it is just how our brains, and our cultures, work. But you can change and help make a difference.

Bonus:

Want to learn easy ways to reduce your water use in the kitchen? Listen to this helpful Green Divas, What You Can Do podcast with Jessica Arinella.

[dynamic-sidebar id=’Custom Widget 2′]

Greg Laden is a biological anthropologist and science communicator, who writes for ScienceBlogs.com. His research has covered North American prehistoric and historic archaeology and African archaeology and human ecology. He is an OpenSource and OpenAccess advocate. Greg’s wife, Amanda, is a High School biology teacher, his daughter Julia is a world traveler and his son Huxley is 2. You can follow Greg on twitter @gregladen.