what's the science? and should i drink it?

November 30, 2009 5:43 PM

my mother used to put a few drops of hydrogen peroxide in milk to keep it fresh past the 'use by' date. it appears to work. very well. what's the chemistry behind this? and should i drink it?
posted by msconduct to Computers & Internet (16 answers total)

A little Googling turned this up; seems like it activates the existing antibacterial properties of the milk somehow:

The workshop provided a valuable opportunity for experts in the region to exchange ideas and information on all areas of milk handling collection and preservation. It was noted with satisfaction that the implementation of milk preservation by activating its antibacterial system[,]using the lactoperoxidase-hydrogen peroxide-thiocyanate method may greatly benefit all countries in the region.

Never heard of this, but if it works it works. And as for ingesting hydrogen peroxide, some people gargle with it. I'd assume the parts per million in a gallon of milk would be comparable to what you might ingest by accident when gargling.
posted by littlerobothead at 5:50 PM on November 30, 2009 [1 favorite]

Here's the second Google result for milk "hydrogen peroxide"
posted by flabdablet at 5:52 PM on November 30, 2009 [1 favorite]

Interesting. I wonder if the perixidase is still active on pasteurized milk or if the direct oxidative damage to bacteria by the H2O2 is enough by itself.
posted by Fiery Jack at 5:58 PM on November 30, 2009

If that worked, why wouldn't the dairy put a little H2O2 in the milk before they sell it and make the date farther out?
posted by ctmf at 6:04 PM on November 30, 2009

If I had to guess at the biochemistry, it may be an equilibrium question.

Lactic acid bacteria sour milk by converting lactose (milk sugar) to lactic acid. Some of these bacteria also make hydrogen peroxide as a means of keeping competing bacteria from eating lactose.

At a high-enough external concentration of hydrogen peroxide — a concentration that might be dangerous to the lactic acid bacteria — through feedback mechanisms a bacterium's machinery for converting lactose may perhaps also be slowed down, in order to slow down general consumption of lactose and slow down bacteria growth and slow down its own hydrogen peroxide production — all of which in turn slows down the souring of milk.

I have no idea if this is safe to drink. Some people use peroxide as a mouthwash, but I haven't heard of people drinking it. In sufficiently high concentrations it can do some damage.
posted by Blazecock Pileon at 6:05 PM on November 30, 2009

It would probably be safe but the pulse of radicals released from the peroxide decomposition would oxidize a lot of vitamins and probably cause some rancid flavor
posted by Fiery Jack at 6:20 PM on November 30, 2009

I guess my (potentially baseless, idiotic) concern would be that the hydrogen peroxide would inhibit the growth of the nasty sour-tasting bacteria but wouldn't happen to inhibit whatever sick-making bacteria there might be.
posted by palliser at 6:21 PM on November 30, 2009

Response by poster: i can vouch that it does work. i was adding a little (just a couple drops does it) hydrogen peroxide to some milk that's slated to go bad in 2 days when it occurred to me that 1) i've never heard of anyone else doing this, 2) no one i've ever asked seems to have heard of it, and 3) it might not be the smartest thing in the world to do. but i get tired of grabbing the milk for something i'm making & then seeing it's past the expiration date & it's turned bad. of course i'd probably like it less if the hydrogen peroxide ate holes in my stomach & i started to foam at the mouth.

thanks for the answers so far!
posted by msconduct at 6:26 PM on November 30, 2009

A silver dollar in the bottom of the milk can helps keep milk fresh, pdf
posted by hortense at 7:18 PM on November 30, 2009 [1 favorite]

Best answer: A great idea. The WHO actually advises using it as a milk preservative (.1 g to .4 g pure H2O2 per liter) in developing countries, in emergency cases, in conjunction with heat treatment. WOW! pdf
posted by wayofthedodo at 7:40 PM on November 30, 2009 [2 favorites]

If that worked, why wouldn't the dairy put a little H2O2 in the milk before they sell it and make the date farther out?

The dairy would prefer that you buy a new container every week whether you drank it or not. Making the milk last longer is bad business.
posted by Mayor Curley at 11:35 PM on November 30, 2009 [4 favorites]

Yeah, my grandmother did this. I'd forgotten until now.
posted by rokusan at 1:59 AM on December 1, 2009

Response by poster: thanks, everyone! it appears that i'm not going to keel over from 'dosing' my milk, and now i have a little better understanding of why it works.
posted by msconduct at 2:22 AM on December 1, 2009

It sounds like there is science behind this working, but be sure not to get sucked into a confirmation bias. Just because something has an expiration date stamped on it doesn't mean that it is automatically bad on that date.
posted by John Frum at 2:50 PM on December 1, 2009

Response by poster: just in case anyone checks this thread, let me say that this not only works, it works stunningly. i added a few drops of hydrogen peroxide to a quart of milk with about 2 days left before the expiration date. three weeks later i pulled it out of the fridge & used it in a boxed noodle dish. yes, i smelled it before i used it, and tasted it, too. it was fine. and almost a month later, i'm still alive. yeah for science!
posted by msconduct at 2:09 PM on December 31, 2009 [1 favorite]

Keep in mind, the date stamped onto most milk containers isn't an expiration date. It's a sell by date. That always kinda bugged me.
posted by 2oh1 at 4:06 PM on May 20, 2010