What Causes Black Spots on Dishes in Dishwashers

May 22, 2022
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Getting Rid of Those Unsightly Black Spots

Seriously, there’s nothing more aggravating than opening the dishwasher only to discover dirty dishes.

You have the expectation that these efficient appliances perform the tasks they’re designed to do. But honestly, people neglect their dishwasher’s interior.

Many people habitually overload trays, slap a tablet or pod into the receptacle, and wham! expect sparkling clean dishes.

Photo of a dirty glass from the dishwasher

Holding up a dirty glass that just was washed in a dishwasher

So what happens after prolonged neglect of a dishwasher? The results are dirty, poorly washed, and black spots on dishes.

While you may have invested in the top-of-the-line appliances like a KitchenAid dishwasher or high-performance unit like a Bosch, everyone is susceptible.

If this is happening to you, here’s how to tackle the problem of black spots on dishes.

Inspecting the Dishwasher Interior for Damage

When dishes come out dirty, obviously there is a problem. Even after running the extended cycle, you may find more black spots.

Open your dishwasher and examine the interior for potential culprits:

  • Did your dishwasher blow a gasket?
  • Is your dishwasher old and experiencing a corroded heating element?
  • Could it be mold?
  • Are food particles like coffee grinds trapped in the basket filter?
  • Is the rubber lining deteriorating and making its way into the wash cycle?
  • Are the spray arms causing the problem?
  • Are you using a poor quality dishwasher detergent and rinse aid?

If the culprit isn’t apparent, you may have to dig deeper to find the clogged filter basket. If you don’t know where the dishwasher filter is, read on.

Trying One More Trick of the Trade

Before we tackle the dishwasher’s interior and start dismantling it, try a vinegar bath.

Dishwashers work hard. Don’t despair yet.

Vinegar bath method:

  • Pour 3 cups of white vinegar into the base of the dishwasher (making sure it can hold the liquid)
  • Choose the dishwasher’s longest deep clean cycle
  • Allow the vinegar bath to dissolve built-up grease and food gunk
  • The vinegar may dissolve blocked spray holes in the sprayer arm

Vinegar is a powerful cleaning solution; however, it’s not a disinfectant like bleach and other harsh chemical cleaners.

If the problem persists, follow the next set of steps.

Taking the Dishwasher Apart

The first step is to take out the dish racks so that you can dive into the cavity of the dishwasher interior. While you got the racks in your hand, examine them for deterioration. Set them aside.

Photo of the interior of a dishwasher

Analyzing the inside of your dishwasher for clues

  • A good resource for troubleshooting is your dishwasher manual.
  • Put on some protective gloves. There’s going to be some unpleasant gunk from food and grease particles.
  • Somewhere on the base of the dishwasher is the drain filter. It’s a filter or basket-like attachment you can pull or screw out.
  • Wash the basket in warm soapy water. If a clogged basket is causing the black water spots on dishes, it may be instantly noticeable.
  • When your head is in the interior cavity of the dishwasher, scour the spray arms and back areas.
  • Hard water, constant use, and age can cause deterioration of the spray arms. Some dishwasher models have one arm on the bottom and another to spray the top tray.
  • Use a flashlight to get a good look at the tiny holes. Mold or debris may be blocking the holes.
  • Like with the filter basket, clean them with warm soapy water. Scrub with a nylon brush and use a toothpick if the holes are clogged.
  • If you have a mold problem, it will be evident. (Wear a mask.)
  • If the black spots are from a deteriorated gasket or rubber liner, replace them or have a professional fix the problem. (If it’s a gasket/liner, your dishwasher is likely leaking.)

How to Treat a Mold Problem Inside the Dishwasher

Mold is unhealthy and can cause serious problems. In a survey conducted by a medical study, 62% of dishwashers contained some mold. Some even contained potentially harmful mold spores.

Mold can grow in 24-48 hours.

White or cleaning vinegar should tackle most mold. As a bonus, it will dissolve hard water stains. In some cases, a more powerful solution like bleach can destroy mold. However, never use bleach products on stainless steel models or parts. Opt for white vinegar instead.

Add baking soda to a regular maintenance cleaning cycle for an extra clean. Baking soda is effective for removing stains. It helps dissolve food particles. Using a vinegar solution creates a powerful foaming reaction that deodorizes and cleanses and removes mold.

Increase the Dishwasher’s Hot Water Cycle

Intense heat is part of the dishwashing cycle. Average dishwashers heat the water to 120 to 140 degrees Fahrenheit. Stainless steel interiors may get even hotter and reach 180 degrees Fahrenheit.

Water sanitizes dishes and utensils at those temperatures and helps dissolve food and grease.

If your dishwasher model can’t produce those high temperatures, try upping your hot water tank’s temperature.

Before starting your dishwasher, run the hot water in your kitchen sink to speed up the hot water reaching the dishwasher.

Plumbing pipes connect your dishwasher to your kitchen sink. If you have a garburator, try running it before starting the dishwasher to flush residual food waste down the line.

Routine Cleaning Maintenance

A dishwasher needs some tender care too. A monthly cleaning schedule will help prolong the unit’s lifespan. The real bonus is that the black spots on dishes in the dishwasher will vanish whenever you open that door.

Photo of a woman with a dirty glass of water

With proper treatment and prevention, you won’t be dealing with dirty glasses anymore

Tips for preventing hard water and black spots:

  • Fill the dishwasher correctly to conserve water and energy but don’t crowd it
  • Don’t over rinse the dishes that go in the dishwasher; dish detergent needs grease and food particles to create the perfect cleaning combo
  • Run a dishwasher cleaning cycle monthly

Frank Salvatore

Hey there - I'm Frank Salvatore. I created this site as a comprehensive kitchen resource. You'll find everything you need to know about everything in your kitchen. From appliances to utensils and layout - it is covered on this site!

About Me
Frank Salvatore
I created this site as a comprehensive kitchen resource. You'll find everything you need to know about everything in your kitchen. From appliances to utensils and layout - it is covered on this site!
Learn More About Me
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