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Blood, Sweat, and Cocoa: How We Test Washing Machines

To test how well a washing machine cleans, we start with stains


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You've probably never had blood, sweat, cocoa, wine, and motor oil on your clothes at the same time—unless you happened to be present at the 1988 Nakatomi Christmas party. However, it's certainly not unreasonable to expect five of the toughest and most persistent stains to occasionally show up in your hamper. After all, we do encounter stains like these all the time. Since each of these substances represents a different genre of stain, we use fabric strips with each stain to evaluate washer performance.

The standardized stain strips used in washing machine testing. Left to right: clean cotton, sebum, carbon/motor oil, cocoa, red wine, and blood. Top: pre-wash, bottom: post-wash.

In its arsenal, a washer has three stain-fighting tactics: chemical (detergent), mechanical (agitation), and thermal (hot water) action. In order to defeat all five stains, washers must excel at all possible combinations of these three cleaning tactics, because each stain is so different. With the naked eye, it's not easy to see exactly how they're different, but if you take a closer look, each stain presents its own clear set of challenges.


These little oxygen carriers will permanently stain clothes if treated incorrectly.

Our red blood cells owe their color to the protein hemoglobin, which does all the heavy lifting when it comes to supplying your body with oxygen. But while we owe our continued existence on this protein, this nested structure is the source of some of the worst stains.

As far as stains go, hemoglobin is actually quite soluble in water, so it's relatively easy to remove. But if the water is too hot, the protein undergoes a destructive process called de-naturation. Once denatured, the physical characteristics of the hemoglobin are altered to the point that it becomes very difficult to dissolve in water, soap, or anything really. So if hemoglobin denatures while soaked into your shirt, it’s pretty much game over.

The best strategy for removing bloodstains is using soap to burst, or lyse, the red blood cells and cold water to remove the released hemoglobin protein without denaturing it. In washing machine testing, the bloodstains serve to test the washing machine’s ability to maximize protein-lifting action. If a washer does well with blood, you should expect this to translate to all protein based stains, such as grass (chlorophyll) and tomato sauce (lycopene) problem situations.


Ring around the collar? Blame it on sebum, a lard-like secretion that coats your ski and stains your shirts.

While pit stains and visible lower back sweatiness are only temporary sources of self-consciousness, sebum—the oily, waxy substance excreted along with sweat—is quite a bit more permanent. Every skin pore secretes sebum, which forms those yellow stains that plague lightly colored clothing.

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While odorless by itself, the breakdown products formed during the digestion of sebum by naturally occurring skin bacteria possess a distinctive and unpleasant odor. Propionic acid, the main breakdown product, smells very similar to vinegar, so it’s responsible for that sour smell that permeates most densely packed spaces, such as most public transport and concert venues.

Since it's both unsightly and smelly, the fact that it's also tricky to get out of clothing makes it one of the more annoying bodily excretions. Primarily composed of oils and wax, sebum needs a strong surfactant dissolved in water to break up the particles. Therefore detergents coupled with a lot of elbow grease (creating more sebum?) is the best strategy to take care of this sort of stain. Any washing machine that excels at mechanical action, when combined with detergent and some hot water, should make short work of the sebum stain.


Hot cocoa is delicious, but dried cocoa is a stubborn stain.

When Ben Franklin compiled his very thorough list of life's certainties, he forgot one: when a kid eats chocolate, some ends up on his shirt. Clearly, to be considered worthy every washer must be tested in a trial by chocolate.

Chocolate is notoriously difficult to remove from fabric once set in due to its chemical make up. Like most foods, chocolate is a complex substance comprised of organic chemicals, including those pigments that give chocolate its typical brown color. Those organic chemicals can be quite insoluble in water and are actually very effective coloring agents, meaning you need to get rid of almost all of the pigments to ensure that the stain becomes invisible.

Much like wine stains (discussed below), the combination of insolubility and dye efficiency makes chocolate stains a challenge to remove. But if the washer is able to lift this stain using a combination of chemical, and mechanical action, it will likely perform equally well at removing all organic pigments found in naturally occurring food.

Motor oil

There's a reason mechanics wear uniforms. Oil will stain your clothes.

To simulate the byproducts of the weekend DIY oil change, our testing strips include a square contaminated with motor oil and carbon. Being the "opposite of water," removal of this particular stain relies heavily on the washer's chemical action to make the oil soluble in water. This solubility can be enhanced by raising the temperature of the water and soap mixture, so washing machines that effectively use a combined strategy of chemical and thermal action perform especially well.

The carbon particles deposited in the fabric are harder to remove, since they're neither soluble in water nor oil. Carbon is not very reactive, at least in this form, so washing machines need to resort to mechanical action to effectively remove this residue, literally rubbing it out. Much like the sebum stain, this test covers the ability of the washing machine to produce the scouring effect necessary to remove stains that are impervious to water and soap.

Red wine

Forget about terroir, nose, and aftertaste. We only care if red wine washes out.

Unbeknownst to most, red wine doesn’t actually start out red. Like most grape juice, squeezing cabs or merlots actually yields a light yellow juice. It's not until a few days into the fermentation process that the liquid picks up the red and brown pigments from the added grape skins.

Those red and brown pigments are the real cleaning challenge once the red wine is soaked into the garment and the stain is set. The problem with these pigments is two fold: they're very good dyes—meaning you don't need much to make something look reddish brown—and chemically they're very sticky molecules that aren't that water-soluble.

Some people use white wine to remove red wine stains (after all the pigments were dissolved in wine), but we have yet to run into a washing machine with a wine dispensing function. Soap is quite ineffective at removing these pigments, and even cold water and scouring don't usually remove all the stain.

Realistically, as most experienced oeneophiles know, red wine stains aren’t coming out without bleach. The engineers that build washing machines and create the tests to put them through their paces are also aware of this fact, so they included this stain type to test for the machine’s bleaching ability. If a washer can bleach well, it should pass this test with flying colors—or rather without them.

Coming clean

Everyday, we ask washing machines to remove a variety of stains, each representing one of almost infinite removal requirements. But they only have three tools to do so: water temperature, chemicals and motion. Using real-life stains we investigate how well each washing machine wields these tools to remove all evidence of your worst day (or best party), giving you the best possible picture of performance. So go ahead and get dirty, we will let you know which washer has got your back.

Contributing Author: Ethan Wolff-Mann

Photos by wellcome images CC-BY-SA-3.0, Chiot's Run CC-BY-SA-3.0, 3liz4 CC-BY-SA-3.0, ollesvensson CC-BY-SA-3.0, jiannone CC-BY-SA-3.0

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