Why Does Milk Curdle When It Goes Bad?
Ғылым және технология
Most foods fall apart when they go bad - so why does milk clump together? The answer is bacterial poop, and Lauren can explain.
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So, we’ve all seen things go bad. That banana you really did intend to eat, last Tuesday’s leftovers, Anakin Skywalker, your relationships.
When most food goes bad, you’ll see mold slowly eating holes in it, or maybe a film of slime as bacteria break the food down. But milk doesn’t fall apart when it goes bad: It clumps together.
The simplest answer to why this happens is that bacteria have really interesting poop.
Actually, poop in general is pretty fascinating. By studying excrement, you can learn a lot about an animal -- human animals included -- or even an entire community.
But the bacteria we’re interested in today are of the order Lactobacillales, commonly called lactic acid bacteria because they excrete lactic acid.
Some species in this order (Lactococcus lactis, for example) hang out in soil, grasses, and vegetables all over the world. When milk-producing animals eat that produce, the bacteria pass into their milk. Even pasteurization, which is the process where stuff like milk is gently heated to kill off bacteria, can leave trace numbers of them.
These critters love to eat lactose, the natural sugar in milk. They break it down during digestion, releasing lactic acid as a byproduct. (It’s technically a type of fermentation of the milk sugar.)
Milk is an emulsion, which is the science term for a mixture of things that don’t usually mix. The things, in this case, are water and fats.
Under normal circumstances, fats and water repel each other. But milk also contains complex protein chains called caseins that are made up of both hydrophilic (or “water-loving”) and lipophilic (“fat-loving”) particles.
When presented with both water and fats, caseins grab bits of fat and cluster up into globules called micelles, with the fat on the inside and the hydrophilic bits on the outside.
The hydrophilic particles grab onto electrons in the water, meaning that each micelle winds up having a negative charge. And since negatively charged particles repel each other, the globules suspend themselves throughout the water in order to keep their distance. Thus, milk is an emulsion!
But that changes when you add lactic acid into the mix. Acids are sour-tasting compounds that react with water, releasing positively charged hydrogen ions.
So when bacteria multiply in your milk and produce a bunch of lactic acid, it reacts with the water there, releasing a bunch hydrogen ions. These positively charged particles latch onto the negatively charged micelles and neutralize them.
With no force keeping the micelles apart, they clump together. So you wind up with sour and lumpy -- aka curdled -- milk.
And, OK, that’s pretty gross and unfortunate if you were hoping to have some milk & cereal or put some cream in your coffee. But chemically speaking, this process is awesome!
A controlled version of it is the first step in making yogurt, cheese, and sour cream. We also put lactic acid bacteria to use in fermenting sugars to create lots of foods, like chocolate, kimchi, pickles, miso, sourdough bread, and cured meats and sausages.
SOURCES:
textbookofbacteriology.net/bac...
biotechlearn.org.nz/focus_stor...
bioinfo.bact.wisc.edu/themicro...
www.boston.com/business/articl...
ajcn.nutrition.org/content/73/...
www.wired.com/2013/08/microbes...
chemwiki.ucdavis.edu/Physical_...
www.sciencedirect.com/science/...
microbewiki.kenyon.edu/index.p...
Пікірлер: 95
I’ve been making pasta for a few years now and 2 or 3 times I’ve made lasagna sheets that fall apart instantly when hitting the water. I couldn’t figure out why it was happening. I speculated that a coworker maybe filled the flour bins with the wrong flour (pasta,pizza,bread,ap). I’d love to see an episode on the science of pasta. How it holds up, why it can fall apart and the reasons they’re different shapes. Could be helpful to a lot of people
@patrickmcdaniel2048
3 жыл бұрын
I remember having the same problem at one of the restaurants I worked at where we made fresh pasta. We made the pasta using only semolina and water. Check the water temperature in your mix for consistency.
I drank some milk today, and its not outdated! it goes out in like november (its august) and it had small, small chunks in it... now im worried.. because i drank it 😅 (The milk is a special milk that doesn't go outdated before a few months. i also had it in the fridge)
love your videos im hooked. thanks for the education
thank u so much! very informative :))
"Anakin Skywalker, your relationships" hahahahah Well, at least fermentation produce good foods, hahahah
@BrainStuffShow
8 жыл бұрын
+PratoFundo Fermentation creates basically all my favorite foods. /Lauren
@david09baz
4 жыл бұрын
BrainStuff - HowStuffWorks OMG YOU COMMENTED SOO COOL!! Hello! Please reply.
Does baking soda stop milk from clumping, if so could you keep the milk outside the refrigerator?
so what's the difference between yougurt and rotten milk?? both are caused by bacteria right ?? ..plz elaborate..thanks.
@PianoRootsMusic
6 жыл бұрын
yogourt has specific bacteria that are good for you, but rotten milk is filled with a bunch of random, potentially harmful bacteria
why does milk boil with froth for the first time and later, after 2-3 boils, it never comes up to the level of spilling ?
This answered alot my questions to the conversion of milk to cheese. Thank you! Can you do an extended version of this video on the whole conversion of cheese to milk?
I came here hoping to see why it works equally in plant and animal milks. I suspected it had to do with positive and negative ionic interactions, so that was neat, but I'm still not sure if it counts as an emulsion and that the process is the same since lactic acid shouldn't be a part of it AFAIK.
If curds and whey are left when lacto bacilli is present, where is the lactic acid and how do you separate it?
BrainStuff please make an episode with "Why people like evil thinks and thoughts " i mean really. All of us enjoy being bad and evil, feel that power hunger. What make us feel so good when we do evil thinks?
"Poop in general is interesting."
Thanks for all this useless knowledge birdtree, it really helps me procrastinate
@benjadoo
6 жыл бұрын
lmao
@nona8009
5 жыл бұрын
Actually this was so helpful
is that micelles similar to that soap micelles?
Milk and Cereal, Milk and Cereal, Milk and Cereal, Cereal and Milk
@nickcastaneda203
6 жыл бұрын
Jasperro fuck you
I just drank a carton of milk that curdled, nothing happened to me. The first day I just drank the clumps. The rest I filtered the big clumps. It had no smell or bad taste and that's why i drank it.
Curdled milk is not bad food, bovine mammary secretions are for bovines, not human food.
i thought you were Lee Ann Mcadoo at first.
i was eating!!!!! my apple... omg
Does lactose free milk not curdle?
I will never look at milk the same again😧
you guys are gr8 and your videos too bt you shld change your background image and music like seriously :)
@jalendarius
7 жыл бұрын
ashole
My 10 litre milkes always crudles.what to do.i am in huge lost.save me.give me a suggestion
moldy, stinky milky! Let's Goooo!!
in northern india and pak people do the control version to make yogurt
What's the noise made when you "crack" your neck?
@BrainStuffShow
8 жыл бұрын
+stephen johnson Good question! It's probably the sound of a tiny air bubble forming inside the fluid in the joint, created when you stretch the joint by moving your neck. It'd make an awesome video -- thanks for asking! Here's a report on knuckle cracking in the meanwhile: www.npr.org/sections/health-shots/2015/04/15/399636388/why-knuckles-crack
so why can you eat yogurt but not curdled milk
@maanyavgangaraj8624
7 жыл бұрын
yogurt has a lot more stuff in itthat curdled milk.
Isn't milk an emulsion due to the homogenization process? In unhomogenized milk, the cream (the part with all the fat) rises to the top.
@filkz4530
8 жыл бұрын
Maybe it's both
I just looked down at my cereal and it has curds in it.......
I came here because of the term “blood-curdling” from Inside Edition 🤪
*God has entered the chat* God: Brainstuff, if you reply, you shall be granted 500 years of life. *God has left the chat*
Why the fuck is everyone scared of eating curd, lassi is made from the same thing. Stop drinking mango lassi then!
I love Lauren's videos the best and not just because I'm secretly in love with her...I just love her presentation style, speaking pace, and voice tone. Another great video! More Lauren! :)
safe to drink curdle milk as yoghurt?
@BrainStuffShow
8 жыл бұрын
+Youngboon Lim Yes! Controlled versions of curdling create completely safe food products like yogurt and cheese.
@youngboon1
8 жыл бұрын
BrainStuff - HowStuffWorkssorry no I mean, drinking overnight milk is it safe
@suharsh96
8 жыл бұрын
+BrainStuff - HowStuffWorks what about the milk that got curdled by itself ? is it safe to consume?
@suharsh96
8 жыл бұрын
+BrainStuff - HowStuffWorks what about the milk that got curdled by itself ? is it safe to consume?
Milk has officially gone bad.
why does almond milk go bad after 7 days
@gavinb2
8 жыл бұрын
It definitely does not
If they're negatively charged it makes sense they force themselves to be well distributed. But why would they clump when they're neutral? Clumping seems to imply attraction, why are neutral mycelles attracted to each other?
@BrainStuffShow
8 жыл бұрын
+raydredX Even though they don't have a charge, the outside layer of the micelles are still hydrophobic. So when they happen to run into each other via the entropy of the milk system, they latch onto each other. It's not as strong a force as charged attraction. That make sense? /Lauren
@raydredX
8 жыл бұрын
+BrainStuff - HowStuffWorks Thank you so much for the reply! Hydrophobic implies it's not attracted to water. (if it meant it repelled that would be enough to explain it) So why does the entropy favor them latching together?
@yuwerlyk8506
6 жыл бұрын
+BrainStuff- HowStuffWorks Wait... So its not dangerous to drink it? with clumps in it? because my milk is not outdated and it already had small, small chunks in it. But the chunks are not like CHUNKS, they are just small pieces.. :O And i kind of drank it so...
Now i can make cheese
Madd science
why did i watch this video? i probably could have explained it better
@BrainStuffShow
8 жыл бұрын
+aajjeee If you make your own video about the topic, we'd love to see it! ^__^
@aajjeee
8 жыл бұрын
BrainStuff - HowStuffWorks i mean this figuratively, im a chemist so it was pretty obvious for me.
@aajjeee
8 жыл бұрын
i dont technically have a bac yet but its just chemistry, you dont need biochemistry to know that polar and non polar liquids dont mix, or that this is what milk is, as for lactic acid, you can already know it because of the ''vinegar'' smell of sour milk
@aajjeee
8 жыл бұрын
its true i didnt know the barteria was already in the grass before the cow ate it, which is a nice addition
Rotting relationship
that's just yogurt floating to the top. just eat it.
@cookiesncream789
8 жыл бұрын
Why don't you try it first and then report back to us? 😃
@MurtezaAFG
8 жыл бұрын
I'm lactose intolerant ;P But trust me, just eat it.
well milk doesnt go bad its just turning into cheese
@nona8009
5 жыл бұрын
Robert Myers lol😂😂
PBS Studios > Revision3
@BrainStuffShow
8 жыл бұрын
+Caleb Limb Personally, I can neither confirm nor deny whether I agree. But either way, we're not associated with either of those companies. :) /Lauren
I just poured out today a half gallon of milk, that was six months old that did not go sour. Did not clump nor stink. No odor at all, poured just like the day I bought it. What gives?
yeaa first to comment!
So what causes the milk to curtle when put in a paralyzer? Is it the coke? The alcohol? Is it still safe to drink at that point?
@MartijnCoppoolse
8 жыл бұрын
A "paralyzer"? What's that? It sounds like coke with some kind of alcoholic beverage...
@CiderDivider
8 жыл бұрын
+Martijn Coppoolse It's an alcoholic beverage made with coffee liqueur, (typically) vodka, coke and a splash of milk. Sounds kind of gross, but the flavour is lightly sweet.
@MartijnCoppoolse
8 жыл бұрын
+CiderDivider Thanks, I didn't know that one. In that case, the alcohol denatures the proteins in the milk, which causes the curdling. (Also, coke is slightly more acidic, which might speed up the process.) It's perfectly safe, since the dangerous part of milk gone bad is the bacteria (or rather, their excrements). In your paralyzer, there's no bacteria (to speak of), and so no danger.
@CiderDivider
8 жыл бұрын
+Martijn Coppoolse Interesting! I've seen conflicting information when I looked it up in the past, so when I seen this video that quickly came to mind. I know that coke and milk (or other dairy products like ice cream) have an interesting reaction when put together, but wasn't confident on the alcohol portion. And even googling it now, there are all sorts of ways to prevent it when you're mixing the drink, but everyone's got a different answer. Some are pointing at the temperature, others are saying the ratios need to change, and others are saying there's a specific order. I have a 50/50 rate with the curtling haha
@MartijnCoppoolse
8 жыл бұрын
+CiderDivider My answer was indeed wildly simplistic. There's a surprising number of variables at play when making such a mixture. Milk is a suspension, your coffee liqueur probably too, and coke also has a far from straightforward composition. Temperature and the degree of acidity both play a role in whether or not it curdles. And since curdling is not an instantaneous process, having a little milk in a lot of alcohol will produce a different effect than a little alcohol in a lot of milk; which means the pouring order can be important too, and even the pouring speed... A Ukrainian friend of mine once showed me how to pour hot tea with milk _and_ lemon. In that case, it's the lemon's acidity that curdles the milk, so the trick is to use the tea's heat to break down the curdling agent (which tends to break down at temperatures above 70°C). I've managed it a few times, but it curdles more often than not. :-P
why does milk clump together? well Umm because of the bacteria in milk... they produce lactic acid. and the acid makes the protein clump .. it makes the protein "sticky" ... just a one liner ..
ermagherd fihrst
Wowwwwwwwwwwwwwwwwwwww☣🖕
so if I let the milk go bad, basically I made kefir?
forth :)
Are you a transgender?