The Baking Soda answer STINKS!

Hoooooo boy, I think the Advisory Board had better get some advice, preferably from Cecil himself. The answer to the baking soda question wasnt even half-baked. The fact is that baking soda neutralizes acids. I don’t see how this has anything to do with fighting odors.

One could have surmised that any finely-divided substance has some ability to absorb odors. Or that alkaline substances, when dissolved in water, are good at removing stains (aka soap or TSP). These are IMHO much more likely mechanisms for removing odors than just having some random alkaline substance in the fridge.

Tell the truth: you’re pissed because of the Oklahoma remark, aren’t you? I wanted to change it, but Ed said it would be OK.

Anyway, the question goes back to what is the cause of most odors that we find objectionable? Now, one factor to what we perceive as odor is the concentration. What you refer to, using a grainy powdered substance, may help with filtration (although, if you have a fridge odor that’s unusually highly concentrated, baking soda ain’t gonna help anyway). However, the chemical reaction of these odoriferous substances with sodium bicarbonate is why baking soda is a more effective deodorant than a box of salt or sand in the fridge.

In the home, almost all bad smells (outside of the garage) are due to bacterial decomposition. Putrefication, fermentation, and rancidity This is an instinctual reaction; there is nothing unendurable about even the worst of smells (short of toxicicty), but we develop averse reactions to smells which may be harmful to us if we ate whatever was making rhem. In other words, once food starts to go over. (Of course, there are a lot of negative little beasties that can get into food and not cause it to spoil, but anyway…)

In the fridge, you have an environment designed to slow this decomposition, but it does happen for various reasons, and the bacteria produces various products, e.g. acetic acid, diacetyl, putrescine, hexanoic acid, isoamyl acetate, and isovaleric acid, that our noses interpret as bad. Baking soda is also used in litter boxes, where it goes to work on the indole, skatole, and ammonia compounds. What these products have in common is that they are highly acidic or basic. When acids react with sodium bicarbonate, you’re essentially left with a salt of some kind, and an odorless gas. Picture your baking soda/vinegar volcano elementary school science experiment. (I haven’t been able to find in detail what happens when a base is exposed to sodium bicarb, sorry.)

This chemical property is separate from its alkalinity and abrasiveness, which make baking soda an effective cleaning agent in addition to being a deodorant, all of which are separate from the leavening action which the stuff is named after. Truly, this is miracle stuff. If the Messiah comes back, forget the myrrh, give him some Arm and Hammer.

Thanks for the reply. I’m still unconvinced:

(1) You havent proved there even is a phenomenon to discuss. I know A&H have been advertising this as a fact for decades. That doesnt make it true. Does anyone have any facts to back up the claim that baking soda de-smells a fridge? I’d love to see it.

(2) You mention some smelly organic acids, and some smelly bases. Well, that about covers everything. And proves nothing. To make a convincing case you’d have to give some proof that the preponderance of fridge smells are quite acid, and/or that basic smells can react with baking soda. I don’t think either one of these is likely.

(3) You seem to be fixated on the 1st grade science experiment with baking soda and vinegar. Very impressive. But we don’t see that happening in our fridges, do we? Our 2-year old box of A&H is not a frothing mass of bubbles and salts. I’m not going to chemically analyze it, but it looks completely and utterly unreacted. So it seems unlikely that there’s any significant or even noticeable acid/base reaction going on.

I was unconvinced by Arm & Hammer’s ad and box copy too, and looked for other sources. I admit I found no real hard science ,i.e. detailed experimentation, to back it (hey, the Mailbag guys were screaming for an answer, what can I tell you?), there were numerous other authors, companies, science and consumer web sites, etc., that made similar claims, and explanations such as the one I gave above. The vinegar volcano (hope mentioning for the second time doesn’t give further illustration of my fixation) is an illustrative example; obviously the reaction with greatly dispersed acidic and basic molecules in the air is not going to be so visible. Perhaps if someone keeps a bos of Arm & Hammer in the fridge, they could open it up and see if there’s any visible change in the stuff, although I doubt it. Obviously, my answer was based on research, not on any definitive knowledge of the chemistry involved. If anyone wants to comment authoritatively on this situation, and tell me if and where I screwed the answer up, it would be appreciated. In the mean time, clearly more research is called for. Not necessarily by me, cause I don’t care that much.

Kidding! I’ll hit the library when I get some time off work (week or so, max).

I can just say this: I was a college student for three years, and I’ve seen fridges that would make you puke to look in them. Fridges with a box of baking soda smell better, given similarly aged contents. If I open a fridge and can smell rancid food-type smells coming out, it ain’t got a box of baking soda. (If it does, the owner needs to die for being that much of a slob…you’ve gotta try hard to get to that point.)


Naggy

“I am an Anarchist. The reason I don’t promote Anarchy is because I don’t trust you idiots.” -anon

Word is, yes, my refrig does smell better with the baking soda.

However, isn’t also possible that baking soda has it’s own odor and therefore masks the odor of any food?

It doesnt seem all that plausible that all the air in the refrig circulates thru the box of soda. It seems more plausible that the box releases it’s own odor.

Sodium bicarbonate just isn’t a buffer, because sodium ion is not an acid. Baking soda won’t tie up bases (amines like indole or various rotten-meat ptomaines), or relatively neutral things like ketones, esters or thiols (the reigning kings of stench).

Most smelly things aren’t carboxylic acids. So if baking soda reduces odors generally – and in an answer starting “it really does”, I’ve got to say I was looking forward to some evidence of it – there’s some other effect at work.

(The usual folklore says adsorption. No, salt and sand are not good adsorbents, but I bet activated charcoal could filter fridge air as well as tap water. Sitting in a box, I don’t know, and baking soda, I have no idea.)

My guess is that baking soda is hygrophilic and that it acts in some respect as a dessicant. Perhaps it doesn’t actually remove the odors but by making the air drier makes it harder for us to smell the offensive stench. Ever was down a trash can?

The answer to this dilemma was pretty obvious to me, probably because I’m attacking it from a differnet angle than you guys did. You guys are taking a microscope to a problem that deserves a much wider perspective. Lots of things stink, but we’re examining “refrigerator stink” (NOT decay stink, there’s a world of difference which I’ll explain below) and that narrows the field tremendously.

Point #1: Bacteria and fungi are the ultimate causes of the majority of stink in a refigerator.

Most of the other sources of stink will tend to diffuse out naturally, but stench with bacterial and fungal origins will build up continuously. What kinds of waste products do bacteria and fungi produce? Oh lots of things, but remember we’re only looking at the ones you’re going to find in a refrigerator. Now, you cannot look at these bacteria and fungi like you look at other cells. Bacteria typically alter their entire metabolism for the breakdown of the most abundant energy source, and the fungi your likely to find in your refrigerator are anaerobic.

For example: In milk, the bateria will quickly reorganize their metabolism to break down carbohydrates. Bacteria that try to breakdown proteins and fats, while carbohydrates are the primary energy molecule in the mix, will quickly become an insignificant part of the total population. Remember that bacteria reproduce exponentially until they’ve reached the capacity for their environment, so in an environement with half the bacteria running at 100% and half running at 98%, the 98% individuals will be virtually extinct within hours.

Point #2: The primary source of any refrigerator stink will be the immediate byproducts of the breakdown of the most abundant energy molecule in the mix (bacteria’s contribution), and the breakdown of sugars (fungi’s contribution).

Point #3: The most abundant energy molecules in a refrigerator will be sugars. The low temperature of a standard refrigerator prevents bacteria populations from reaching the levels needed to create an environment in which all of the carbohydrates would be broken down (at which point the fauna would have to resort to breaking down other molecules). Besides, most people will have thrown the food out before this could happen and baking soda would hardly be expected to tackle that level of stench, even if it were effective on it.

Conclusion #1: Bacteria will break down sugars aerobically and aerobically. Fungi will break down sugars anaerobically. The primary source of smell products will be anaerobically breakdown of sugars.

Point #4: The products of the anaerobic breakdown of sugars are (surprise surprise) acids in most fungi and bacteria.

Conclusion #2: Most of the stink in your refrigerator is directly caused by acids. I’ve also noticed that “refrigerator stink” bears more than a passing resemblance to the smell of rising dough (pre-baking, of course), which would tend to support this conclusion.

Point #5: In any chemical reaction where one reactant is suspended and the other stationary, the reactant will eventually be consumed to its equilibrium point (what that is for baking soda, I don’t know, but the volcano experiment seems to indicate that it greatly favors the products).

This is due to simple diffusion. The suspended reactant will tend to spread out evenly throughout the space available. The reactant is being consumed in one area of the space, so the suspended reactant will appear to be drawn to the stationary reactant until equilibrium is reached. If the reaction favors the products strongly enough and there is sufficient stationary reactant, the suspended reactant will eventually be almost entirely consumed.

Conclusion #3: Baking soda has the potential to consume anything which it will react with in an enclosed space.

Final Conclusion: Baking soda, a weak base, has the potential to reduce refrigerator odor. Whether or not this effect is perceptible is still open to debate.

-Bob

Oh, and I almost forgot:

  1. Baking soda will not react with a base solely because of the fact that it’s a base. Any reaction is (for our purposes) incidental to the alkalinity of the reactant.

  2. Why doesn’t baking soda in your refrigerator “look” reacted? Well, what’s the molarity (concentration) of a strong acid smell? What’s the molarity of solid baking soda? I would guess somewhere within a couple orders of 0.0001M and 1000M, respectively. I’m sure you can figure the answer to this one yourself.

-Bob

BTW, the OP (George) suggests that the Straight Dope Staff might want to get some advice from Cecil on this one. Cecil’s behaviour is pretty much unpredictable, but I venture to say it is unlikely that he will intervene in these Mailbag items. Most questions get to the Mailbag because someone has submitted them to Cecil, and he’s not interested in answering them… for whatever reason. So his loyal Staff gets the already-picked-over questions. Thus, it’s unlikely that he’d get involved.

Devilfish said:

I’d welcome refs on this, but just from Bio 101, your classic anaerobic glycolysis takes glucose through pyruvate to lactate. Lactic acid is an acid, but lactate ion is a base.

(Generally: carboxylic acids are more highly oxidized than carbohydrates, so they seem an unlikely anaerobic product.)

Elaborate chemical scenarios are not likely to settle matters. What we really need is four refrigerators: one control, one baking soda, one activated charcoal, and one a dish of 0.01 M NaOH. Plus beer for hiring lab-asses.

Failing that, maybe somebody could take their baking soda out and smell it. If it smells of fridge, it’s probably acting as an adsorbent. The acid neutralization would result in unsmelly aqueous anions (in what, some surface film?) and is poorly reversible because the CO2 leaves. If doesn’t smell, can’t say anything. None of this addresses the actual smell-reduction question…

I’ll work for beer

[[I can just say this: I was a college student for three years, and I’ve seen fridges that would make you puke to look in them. Fridges with a box of baking soda smell better, given similarly aged contents. If I open a fridge and can smell rancid food-type smells coming out, it ain’t got a box of baking soda. (If it does, the owner needs to die for being that much of a slob…you’ve gotta try hard to get to that point.)]] Naggy

Don’t sound like a case/control study to me, but I tend to agree with you. And Devilfish? Either I’m really impressed with your knowledge, or I want to slap you and tell you to get a life. Can’t decide.
Jill

>>I’d welcome refs on this, but just from Bio 101, your classic anaerobic glycolysis takes
glucose through pyruvate to lactate. Lactic acid is an acid, but lactate ion is a base.<<

I can’t comment on the processes involved (despite what you might think, chemistry ain’t my bag, baby), but I can assure you that anaerobic respiration almost always produces acids, and that lactic acid fermentation certainly always produces acids.
This is demonstrated quite clearly when you consider that anaerobic respiration in humans causes acidosis, never alkalosis.

>>Elaborate chemical scenarios are not likely to settle matters.<<

Well, it was really just mean to settle the matter of whether or not baking soda absorbed fridge smells, not whether or not it was effective in that role.

-Bob

>>And Devilfish? Either I’m really impressed with your knowledge, or I want to slap you and tell you to get a life. Can’t decide.<<

Before you make a decision: Keep in mind that if you slap me, I’ll be forced to send my 27 cats and the whole local dungeons and dragons chapter after you…

-Bob

Oops, I forgot to count the protons. Yeah, that’s lactic acid being produced. So I suppose your fridge smells of carboxylic acids, though I can tell you mine smells of sulfinylthioic esters and suchlike right now.
(mmm, garlic butter.)

In lieu of actual data, I searched the web, generating the following semi-amusing factoids:

http://www.armhammer.com/whatis.htm
Arm & Hammer sure does claim that “Baking Soda deodorizes by bringing both acidic and
basic odor molecules into a neutral, more odor-free state”. I can only imagine they’re thinking something about how HCO3- is amphoteric, which doesn’t matter here.

www.armhammer.com/experimentnofr.htm
Curiously, their kiddie experiment page says that “Some unpleasant odors are not caused by acids and will not react with Baking Soda, so Baking Soda will have no effect on the odor.”

www.williamsportmoving.com/tips.htm
Many sites about moving crib the same text saying “fresh coffee, baking soda or charcoal in a sock” will keep your refrigerator fresh.

www.waltonfeed.com/grain/faqs/iif1.html
Many survivalist sites crib text saying that baking soda adsorbs odors so store it in a sealed container.

Executive summary: Arm&Hammer thinks it reacts with acidic odors, and maybe basic ones too somehow. The web at large thinks it adsorbs them. I’m holding out for the four refrigerators.

[[Before you make a decision: Keep in mind that if you slap me, I’ll be
forced to send my 27 cats and the whole local dungeons and dragons
chapter after you…]]

Yikes. I really just meant that as a playful, affectionate little slap (tell him, Ian). But now I’m holding out for Eli Brandt. There’s a guy, knows his baking soda.
Jill

[[Before you make a decision: Keep in mind that if you slap me, I’ll be
forced to send my 27 cats and the whole local dungeons and dragons
chapter after you…]]

Yikes. I really just meant that as a playful, affectionate little slap (tell him, Ian). But now I’m holding out for Eli Brandt. There’s a guy, knows his baking soda.
Jill

>>[[Before you make a decision: Keep in mind that if you slap me, I’ll be forced to send my 27 cats and the whole local dungeons and dragons chapter after you…]]

Yikes. I really just meant that as a playful, affectionate little slap (tell him, Ian). But
now I’m holding out for Eli Brandt. There’s a guy, knows his baking soda.
Jill<<

Oh… I see. Well, dammit, I guess I’m just gonna have to send my cats after Eli then.

Mew.

-Bob