Why the heck did my butter turn purple?
October 15, 2011 5:41 PM Subscribe
Why the heck did my butter turn purple?
I have read all the previous questions about butter-keeping, but nobody has mentioned this kind of weird colour change.
My butter lives in the freezer, except for a small amount that I keep in a white lidded plastic container on the counter. I just now went to make a bagel, and some of the butter has turned lurid bright violet -- this colour. There is nothing spotty or spiderwebby or dark happening, like mold, and it doesn't look rancid -- there's no transparency and no top layer that's darker than the rest. It smells fine. It just looks like a tablespoon of violet paint has been swirled into it: it's quite pretty. I should have photographed it, but I was overcome by squeamishness and destroyed it right away.
For reference, this is my butter: it's German, 40% saturated fat, unsalted. The date on the package is 11.30.11. It lived in the freezer for two weeks, and then on the counter for about a week, where it is fairly cool.
I am super-curious: why would it turn purple? Is this oxidization? Bacteria? Something else?
I have read all the previous questions about butter-keeping, but nobody has mentioned this kind of weird colour change.
My butter lives in the freezer, except for a small amount that I keep in a white lidded plastic container on the counter. I just now went to make a bagel, and some of the butter has turned lurid bright violet -- this colour. There is nothing spotty or spiderwebby or dark happening, like mold, and it doesn't look rancid -- there's no transparency and no top layer that's darker than the rest. It smells fine. It just looks like a tablespoon of violet paint has been swirled into it: it's quite pretty. I should have photographed it, but I was overcome by squeamishness and destroyed it right away.
For reference, this is my butter: it's German, 40% saturated fat, unsalted. The date on the package is 11.30.11. It lived in the freezer for two weeks, and then on the counter for about a week, where it is fairly cool.
I am super-curious: why would it turn purple? Is this oxidization? Bacteria? Something else?
Best answer: Ok, I'm really intrigued by this, so I've done a bit more searching.
This paper is about a method for detecting the amount of whey in cream and butter. Although I have access to almost all academic papers through my university, I sadly do NOT have access to the full text of this paper. However, from the abstract, it seems that the test involves adding Erlich's reagent to the butter. Erlich's reagent then reacts with sialic acid. The sialic acid content of cream and butter apparently varies throughout the year as the cow's diet changes.
Erlich's reagent is, according to Wikipedia, a strong electrophile, 4-Dimethylaminobenzaldehyde.
So, what I'm wondering is whether something similar to Erlich's reagent could have got on your butter and reacted with sialic acid, but it's been quite a few years since I last studied organic chemistry...
I'll keep thinking about it.
posted by Cygnet at 6:35 PM on October 15, 2011
This paper is about a method for detecting the amount of whey in cream and butter. Although I have access to almost all academic papers through my university, I sadly do NOT have access to the full text of this paper. However, from the abstract, it seems that the test involves adding Erlich's reagent to the butter. Erlich's reagent then reacts with sialic acid. The sialic acid content of cream and butter apparently varies throughout the year as the cow's diet changes.
Erlich's reagent is, according to Wikipedia, a strong electrophile, 4-Dimethylaminobenzaldehyde.
So, what I'm wondering is whether something similar to Erlich's reagent could have got on your butter and reacted with sialic acid, but it's been quite a few years since I last studied organic chemistry...
I'll keep thinking about it.
posted by Cygnet at 6:35 PM on October 15, 2011
Oh, sorry, and the salient point is this: the product of the reaction between sialic acid and Erlich's reagent is purple!
posted by Cygnet at 6:35 PM on October 15, 2011
posted by Cygnet at 6:35 PM on October 15, 2011
Best answer: This is just a guess, and IANAMicrobiologist. Weird reddish-purple colors make me think of Serratia marcescens, a pathogenic (but not extremely scary) bacterium that is fairly common, especially in damp conditions. If you've ever seen reddish splotches on your shower tile grout, it was probably S. marcescens. Wikipedia sez it lives on fatty residues in soap/shampoo scum, so I guess it could live in butter. I have no idea how it could have contaminated your butter to that extent, but keep an eye on other foods in your kitchen, since it can live on bread and other moist things. Don't panic, though.
posted by Quietgal at 7:02 PM on October 15, 2011 [2 favorites]
posted by Quietgal at 7:02 PM on October 15, 2011 [2 favorites]
Wow, that is weird. Might it have something to do with the ink?
posted by waitangi at 7:15 PM on October 15, 2011
posted by waitangi at 7:15 PM on October 15, 2011
Crap, format fail. Shoulda closed italics after "marcescens". As long as I'm back here, don't freak out - it's pretty ubiquitous and doesn't necessarily mean OMG DOOM. Also, I could be totally wrong about this. You might want to contact the butter manufacturer and ask them if anybody else has reported a problem. The fact that the pigment was swirled into the butter, as opposed to sitting on top like a typical bacterial colony, sounds like something got into the butter during the manufacturing process.
posted by Quietgal at 7:49 PM on October 15, 2011
posted by Quietgal at 7:49 PM on October 15, 2011
I think this has happened to me when I used a really cheap ass aluminum knife from the dollar store. So I assumed reaction of aluminum and whatever else is in the metal with the chemicals in butter.
posted by cda at 9:17 PM on October 15, 2011
posted by cda at 9:17 PM on October 15, 2011
Response by poster: Hm. There was no metal in the butter, and I've been using the same stainless steel knife as always. So it's not that. And it'd been taken out of the wrapper, so it wasn't ink either.
Erlich's reagent sounds promising, or maybe Serratia marcescens. Thanks!
posted by Susan PG at 11:43 PM on October 15, 2011
Erlich's reagent sounds promising, or maybe Serratia marcescens. Thanks!
posted by Susan PG at 11:43 PM on October 15, 2011
I had a container with cooked chicken residue turn bright purple. I'd say bacteria.
posted by Not Supplied at 6:52 AM on October 16, 2011
posted by Not Supplied at 6:52 AM on October 16, 2011
Trace amounts of starch and Iodine?
The fact that it's mixed in and not just a surface phenomenon suggests that it's point of origin phenomenon and not a in home contamination issue.
posted by Kid Charlemagne at 9:37 AM on October 16, 2011
The fact that it's mixed in and not just a surface phenomenon suggests that it's point of origin phenomenon and not a in home contamination issue.
posted by Kid Charlemagne at 9:37 AM on October 16, 2011
Hi, former cheesemonger here. I expect, as others have said, that you've got some bacteria in play. The counsel we always gave from behind the counter is that it's perfectly okay to cut away green or blue mold, but if you come upon any of the pink/yellow/orange kind, pitch the whole piece of cheese.
That it sat on the counter for a week would certainly create the opportunity for bacteria to reproduce, and if you put a knife into it that wasn't perfectly sterile, it could have started the growth of bacteria throughout the container.
The fact that this is a European butter, and thus possibly a cultured butter, makes me wonder if there is some part of the culture which provides a pleasant flavor profile at a low level and OMG PINK WTF! if it gets to go a bit wild.
posted by jocelmeow at 11:19 AM on October 16, 2011 [2 favorites]
That it sat on the counter for a week would certainly create the opportunity for bacteria to reproduce, and if you put a knife into it that wasn't perfectly sterile, it could have started the growth of bacteria throughout the container.
The fact that this is a European butter, and thus possibly a cultured butter, makes me wonder if there is some part of the culture which provides a pleasant flavor profile at a low level and OMG PINK WTF! if it gets to go a bit wild.
posted by jocelmeow at 11:19 AM on October 16, 2011 [2 favorites]
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posted by Cygnet at 6:07 PM on October 15, 2011