Curdling of Milk Video Lecture - Biology Class 12 - NEET

you might not want to watch this one
while you're eating because today we're
talking about rotting food yay
so we've all seen things go bad 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 but the bacteria that
were interested in today are of the
order lactobacillus commonly called
lactic acid bacteria because they
excrete lactic acid some species in this
order Alecto coccus lactis for example
hang out in soil grasses and vegetables
all over the world when milk producing
animals eat that produce the bacteria
passed 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 that
occurs in milk they break it down during
digestion releasing lactic acid as a
by-product 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 our
water and fats under normal
circumstances fats and water repel each
other but milk also contains complex
protein chains called casein that are
made up of both hydrophilic or
water-loving
& lipophilic or 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 whole bunch of lactic acid it
reacts with the water they're releasing
a whole bunch of 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 that's pretty gross and
unfortunate if you were hoping to have
some milk and cereal or 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 a chocolate kimchi
pickles miso sourdough bread and cured
meats and sausages so what other food
science questions do you have let me
know in the comments and I shall
endeavor to answer them in future
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of course in your source and mine for
lots of curiosity quenchers is
howstuffworks.com