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View Full Version : Coffee grounds as deodorizers: explain.


WoodenTaco
12-30-2008, 01:43 AM
Backstory:
So something died behind our refrigerator recently, and as it rotted the whole fridge was filled with an unspeakably awful smell. Within a few days, it quickly got to the point that opening the door was physically nauseating and the smell would fill the entire house. We emptied the refrigerator and cleaned the entire inside with soap and water while wearing improvised masks (which didn't work all that well). We removed various drawers and washed them, we took out various pieces that the online manual says should be cleaned to get rid of a bad odor. Nothing worked - the smell just continued to get worse.

We called up the refrigerator company to get a technician to help. He came in, and as soon as we told him the problem, he said without blinking an eye, "Grind up a lot of coffee, put it in a bunch of bowls uncovered, and let it sit in there. In one or two days, the smell will be gone."

We found this hard to believe, but he swore up and down it would work. We paid the outrageous service fee ($100 to be told to put coffee in the fridge!) and followed his instructions. And amazingly, it worked. It worked fast, too - the smell was halfway gone in six hours, and in two days was entirely gone.


The Question:
How does this work? Why do coffee grounds get rid of bad odors? You don't even need to smear them around or disturb them often - just leaving them out in the air gets rid of the smell.

panache45
12-30-2008, 02:59 AM
So . . . at what point did you discover the rotting thing, and is it still back there?

clayton_e
12-30-2008, 04:55 AM
The OP isn't coming back. We can guess, but I'd assume it ate him.

Reply
12-30-2008, 06:14 AM
Hmm. Are they absorbing the odor (like baking soda is supposed to do, I think)?

If so... you MUST brew the coffee and let us know how it tastes! :D

Savannah
12-30-2008, 11:22 AM
I've used the coffee trick, too. We rarely drink it at home, so there's usually some around. It really works a treat on smelly cars and microwaves that someone tried to melt soap pieces in using a plastic container and hit 20 minutes instead of 2 minutes then went and played on the internet until this unbearable cooked burning melted stench of soap combining with plastic in an unholy coupling from the depths of hell came stealing out merrily from the kitchen.

drachillix
12-30-2008, 12:23 PM
We found this hard to believe, but he swore up and down it would work. We paid the outrageous service fee ($100 to be told to put coffee in the fridge!) and followed his instructions. And amazingly, it worked. It worked fast, too - the smell was halfway gone in six hours, and in two days was entirely gone..

So he solved a problem that was making your fridge something you feared opening and now you bitch about $100 service call. The Geek squad would charge you more to plug your computer back in.

sailor
12-30-2008, 01:29 PM
When you have been cutting garlic or onion and your hands stink, the best way to get rid of the smell is to rub you hands with coffee grounds. *USED* coffee grounds. There's no need to go around wasting perfectly good coffee.

Campion
12-30-2008, 01:37 PM
When I was a kid, my mom kept a sock full of coffee grounds in the cooler that we used for camping (one of those big, hard sided ones, and this was the old days before fancy things like "wheels" and "pull handles" so that was a heavy cooler when full that us kids couldn't carry, only dad).

She only kept the sock in there while the cooler was stored in the garage; the sock stayed home when we went camping. The cooler didn't stink, either, although it did have this weird kind of off-coffee smell that even now I sort of associate with camping.

WoodenTaco
12-30-2008, 01:56 PM
So . . . at what point did you discover the rotting thing, and is it still back there?
Yeah, that's today's mission. We're just assuming something died - thats the only thing I can imagine would make this smell.

So he solved a problem that was making your fridge something you feared opening and now you bitch about $100 service call. The Geek squad would charge you more to plug your computer back in.
Chill out, dude, this ain't the pit. I'm fully grateful, and I'd pay $200. I just thought it was entertainingly simple for the money.

Anyone know any of the science behind this?

ftg
12-30-2008, 02:39 PM
I'm guessing something about the grounds being acidic? I.e., baking soda is alkaline and gets rid of the acid smells but sometimes you need the opposite.

robcaro
12-30-2008, 02:46 PM
We always keep a little cup full of coffee grounds in our refrigerator. It works!:D

Stathol
12-30-2008, 03:08 PM
I've never studied coffee grounds under a microscope, but I if I had to make a WAG, this probably works for the same reason that activated carbon (http://en.wikipedia.org/wiki/Activated_carbon) does. Odor-causing molecules that are dissolved in air will tend to cling to any surfaces they touch. I would assume this is because of cohesion and adhesion (the same reason that water clings to the surface of a glass). If these molecules are stuck to a surface somewhere, then you aren't inhaling them.

Activated carbon is fairly inert, chemically speaking. It's "activated" because of its surface area. Draw a straight line from point A to point B. Now draw a wavy line between them. The wavy line is longer, right? And the wavier you make it, the longer it is. This is the classic "length of the shoreline" problem from fractal geometry. The shoreline problem works in higher dimensions, too. A flat surface has less area than a convoluted one, just like your straight line has less length than your wavy line.

Activated carbon is "fluffy" at a microscopic level. It has a very convoluted surface, and therefore has an enormous surface area relative to its volume. Math geeks would say that although the surface has a topological dimension of 2, its fractal dimension is somewhere between 2 and 3.

Long story short, that enormous surface area allows lots and lots of molecules to cling to it, so it's very handy for getting rid of odors. They use "carbon scrubbers" in a lot of industrial applications where strong odors need to be reduced/eliminated. The process is called adsorption (clinging to the surface), as opposed to absorption (diffusing through the surface). I would suspect that coffee grounds have a similarly high surface area, though probably not as high as activated carbon. So on one hand, it's probably not as adsorptive (is that a word?) as activated carbon, but it's probably more absorbent.

Dervorin
12-30-2008, 03:26 PM
As Stathol said, I suspect it's something to do with the fact that coffee grounds are roasted, thus turning them into a form of activated carbon, which allows them to have a huge surface area to adsorb gaseous compounds. In fact, in some cases, it can be more effective (http://jstage.jst.go.jp/article/jos/55/1/55_31/_article) than commercial activated carbon.

The surface areas are truly stupendous, as Wiki notes: "A gram of activated carbon can have a surface area in excess of 500 m, with 1500 m being readily achievable."

butler1850
12-30-2008, 03:42 PM
and I'd pay $200. I just thought it was entertainingly simple for the money.



This goes along with my $1000 snowball. Early in my IT career, I supported wireless networking links, T3 speeds (45Mbps) and higher.

One snowy March morning in Boston, we got a call for service on a link that had gone down. We could find nothing wrong with the equipment, but it was getting very low, to near zero signal to the receiver. On the roof, the antenna, a large drum looking device (http://media-2.web.britannica.com/eb-media/23/4623-004-D018B58A.jpg), was covered in snow. It doesn't take much to degrade high frequency signals.

The antenna was too high to reach from the base of the tower (on a 40+ story building's roof), and while waiting for maintenance staff to bring a very tall ladder (20', to get from the roof to the drum), I speculated that a snowball might bounce the cover material enough to clear the snow. My co-worker had no objection to trying it, and I threw the snowball well, and hit it dead center. Snow fell off, the signal bounced up to full strength, and we went home.

2 men, onsite for 2 hours, plus 2 hours drive time, (8 man hours at $125/hr) = $1000 for a snowball fix. :D They weren't paying for the snowball, but they did pay for my expertise in knowing HOW to throw the snowball to hit in the right place. Makes for a great interview answer, though I don't support that sort of product any more.

</hijack>

As to the OP, I'm going with it being a porous substance, which absorbs the odor, additionally covering up lingering scents not yet absorbed with the much more pleasant aroma of coffee.

China Guy
01-03-2009, 01:10 AM
when my eldest kid hurled on the plane, the UA flight attendant put coffe grounds on the seat & killed the puke smell immediately.

jsgoddess
01-03-2009, 01:15 AM
When I was a kid, my mom kept a sock full of coffee grounds in the cooler that we used for camping (one of those big, hard sided ones, and this was the old days before fancy things like "wheels" and "pull handles" so that was a heavy cooler when full that us kids couldn't carry, only dad).

You went camping before the invention of the wheel?

Um. Ook? :D

clayton_e
01-03-2009, 09:59 AM
As Stathol said, I suspect it's something to do with the fact that coffee grounds are roasted, thus turning them into a form of activated carbon, which allows them to have a huge surface area to adsorb gaseous compounds.

I read the wiki too.. And I just don't understand how roasting something could make it "activated".. Looks to me like activation is simply increasing the surface area dramatically (like baking powder, used for the same reason). But if coffee grounds and baking soda work great for it.. Why not.. oh.. flour or powdered milk?

MikeS
01-03-2009, 10:21 AM
I read the wiki too.. And I just don't understand how roasting something could make it "activated".. Looks to me like activation is simply increasing the surface area dramatically (like baking powder, used for the same reason). But if coffee grounds and baking soda work great for it.. Why not.. oh.. flour or powdered milk?Roasting something doesn't make it activated it increases the amount of carbon (and similar compounds.)

Dag Otto
01-03-2009, 10:30 AM
2 men, onsite for 2 hours, plus 2 hours drive time, (8 man hours at $125/hr) = $1000 for a snowball fix.

Yeah, but at least you threw the snowball. WoodenTaco's guy never touched the coffee.

Declan
01-03-2009, 05:33 PM
So it was not that much of a stretch for beverly hills cop when eddy murphys character mentioned the drugs being surrounded by coffee grounds. Instead of the drug pooches sniffing the drugs, the area would have a more neutral or an absence of aroma ? Or would the dogs just smell the coffee.

Declan

CC
01-03-2009, 06:22 PM
We may have two processes at work here. I buy the thinking that roasted and ground coffee is of a texture that it can absorb lots of molecules. The grounds, provided they're not so small that they're powdery, have ample space between the grains that there's a good chance that coffee can function as an absorbent. But there's also the series of anecdotes that attest to its power to deal with garlic and other substances. I have a different version - when you've eaten garlicy food and you want to lose that taste, you can, if you're tough, chew one or two roasted coffee beans. It de-garlics your mouth. (Of course, you then have to rinse the coffee out, but the problem is solved by that time.) So I think there may be some chemical affinity that coffee, itself, has for some esters or some other pungent molecules, too.

MissGypsy
01-04-2009, 02:57 AM
Once, my husband tried to make microwave popcorn, but he set the microwave for 5 minutes and walked away.

After we cleared the vast cloud of black smoke out of the house and sent the firefighters away, my poor microwave stank. I tried vinegar, baking soda, lemon juice, and finally, coffee grounds worked to get that stench out. I left the coffee grounds in the microwave for about 4 days, and it didn’t stink anymore. I can’t explain the science, but it worked.

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