Here's how your dishwasher gets the perfect clean every time

Or, at least how it is supposed to

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Ever wonder what goes on in a dishwasher? No? Well, until I started working with home appliances, I didn't either. When I was a kid, I always assumed a dishwasher filled to the top with water, swished around, and drained—like a swimming pool for dirty dishes.

But after entering the strange and wonderful world of product testing, I realized that dishwashers are more like a car wash than a swimming pool, and that understanding that car-wash-like nature of dishwashers is key to getting clean dishes.

inside_dishwasher
Credit: Getty Images / deymos
I'm pretty sure I thought dishwashers ran on water, detergent, and wishful thinking.

So whether you’re trying to troubleshoot a problem or just curious, read on to find out what goes on behind the dishwasher door.

Inside the shiny box

One of the key parts of clean, sanitized dishes is hot water. Water temperatures in a dishwasher get as high as 130°F-140°F. The heating doesn’t happen instantaneously, however. Through its external hookup, the dishwasher pulls in water from your water supply. When a cycle starts, water is pumped into a pool at the bottom of the dishwasher. The heating element below that pool turns on, and starts to heat the water.

However, at the same time, the water in that pool is mixed with the detergent and sent into the spray arms found throughout the dishwasher, typically at the bottom and top of the dishwasher, and occasionally beneath the top rack. The water surges through the spray arms, and hits the dirty dishes, hopefully taking some nasty food stains with it. The water eventually drips back into the pool below, where it is filtered, reheated, and sent back out into the spray arm again. The same water is being constantly used and reused, heated and reheated; between the water recycling and the spray arms, it's easy to see how a dishwasher more closely mimics a car wash than a swimming pool for dirty dishes.

suds
Credit: Getty Images / Tinieder
This is what your dirty dishes see.

Once the water hits the desired temperature, the heater turns off, but the pumps continue pushing water through the spray arms. At the end of that portion of the wash cycle, all of the water is drained (that’s often the gurgling sound you hear in a dishwasher), new, unused water takes its place, and the cycle begins anew.

For a front row seat of a dishwasher in action, check out our Inside the Dishwasher videos.

So now that you know how a dishwasher actually works, we can dig into what actually happens during a dishwasher cycle.

The three stages of cleaning

There are three main stages to a dishwasher cleaning cycle: Pre-wash/rinse, main wash, and the final wash/rinse.

Pre-wash/rinse is the first initial burst of warm water through the spray arm that gets all of the dishes wet, but isn’t really aiming to do much cleaning.

prewash
Credit: Reviewed.com / Julia MacDougall
Detergent can be added to the pre-wash part of a dishwasher cycle.

If your dishes are really, really dirty, though, it may be possible to add detergent to the pre-wash part of the cycle if your dishwasher has a pre-wash detergent compartment. The pre-wash is typically only a few minutes long.

The main wash is just what it sounds like: the main part of the wash cycle. The water is heated, sprayed, collected, filtered, heated, sprayed, etc. until the heating unit is turned off, while the spraying continues. At the end of the main wash, all of the water is drained. Depending on the cycle, the main wash can take anywhere from 20-60 minutes, and may repeat multiple times throughout the cycle duration.

The final wash/rinse pulls in new, clean water, and then begins the heating/spraying/filtering/heating cycle. Again, eventually the heater is shut off, while the spraying continues. The final wash/rinse may or may not use detergent. Like the main wash, the final wash/rinse can take 20-60 minutes, and may repeat multiple times throughout the cycle duration.

A graph of the temperature inside the dishwasher over time clearly illustrates the three main parts of a cycle:

dishwasher_time_plot

Caveat: Some dishwashers do not have built-in water heaters—they pull water directly from the source, so whatever temperature water happens to be circulating in then kitchen is the water that gets used to clean the dishes. Washing with cold water may be the culprit behind unclean dishes or an undissolved detergent pods. If this is the case, try running hot water at the kitchen sink (to purge the cold water from the system), and then turn off the faucet once the dishwasher cycle starts. If the hot water at the kitchen sink stays on, it will pull hot water away from the dishwasher when it needs it most.

Depending on the manufacturer, additional rinses, heated drying, or other features may also be included in the cycle, but pre-wash/rinse, main wash, and final wash/rinse are the core aspects of a dishwasher cycle, as seen by the manual sample below.

Program_overview
Credit: Miele
Cycle descriptions for a Miele dishwasher. The water temperature and number of rinses vary for each cycle.

At cycle's end

So it turns out that your lasagna tray has basically undergone repeated water gun attacks from the spray arms that shoot out hot water mixed with detergent for long periods of time. When you pull it out, it's sparkling clean! Huzzah!

(If your dishes did not come out sparkling clean, we have some suggestions on how to deal with that. One other thing to keep in mind: dish placement is very important, since large dishes in placed in the wrong place could block a spray jet's access to other dishes.)

To wrap up, dishwashers are technological wonders that are extremely convenient and time saving. With judicious usage of spray arms and heated water, they can clean your dishes efficiently and without a mess or lots of effort on your part.

So the next time you take your car into a car wash, realize that your dirty dishes are getting a similar treatment in the dishwasher (minus the impact of the drying flappy curtain).

Our editors review and recommend products to help you buy the stuff you need. If you make a purchase by clicking one of our links, we may earn a small share of the revenue. Our picks and opinions are independent from any business incentives.

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Our editors review and recommend products to help you buy the stuff you need. If you make a purchase by clicking one of our links, we may earn a small share of the revenue. Our picks and opinions are independent from any business incentives.
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