Humans have been consuming animal milk products since at least 7,500 years ago, despite not
widely developing the gene mutation to properly digest milk outside of childhood until around
a thousand years later.
The gene that facilitates the production of lactase in the human body, necessary for processing
the lactose in milk- see our video What Causes Lactose Intolerance, typically gets switched
off in adolescence.
Thanks to the rise of dairy as a significant nutrition source, initially largely in cheese
and yogurt-type substances that could be widely consumed due to low lactose content and had
better shelf life, those who had a genetic quirk allowing them to produce lactase into
adulthood flourished, and this mutation quickly spread throughout a relatively large percentage
of the human population over the centuries.
By 4,000 BCE, a dairy economy existed in central Europe, Asia and ancient Egypt, and with it
came disease.
Sicknesses resulting from tainted food have a long history of being an equal opportunity
killer.
There’s speculation that Alexander the Great died of Salmonella resulting from tainted
water, food or, possibly, milk.
King Henry I of England may have died from eating bad eels.
Scholars think that the first Jamestown settlement may have withered away thanks to a Salmonella
outbreak.
“Milk Sickness,” resulting from drinking the milk of a cow that has eaten the plant
White Snakeroot, killed Abraham Lincoln’s mother.
President Zachary Taylor could have died from drinking iced milk.
Point being, food-related illness was a rather common occurrence prior to Pasteur's innovation,
especially milk specific ones.
Due to its organic and nutrient rich nature, milk is one of the most susceptible liquids
to this and only pasteurized milk is considered safe by the FDA, much to the chagrin of raw
milk enthusiasts.
However, there is good reason for concern here.
Even with modern best practices, it's impossible to produce sterile milk and from flora of
the teat canal or udder to fecal soiling to water used to clean the milking equipment,
various microbes will find their way into the milk, not all of them harmless.
For centuries, milk borne illnesses, from tuberculosis to salmonella, typhoid fever,
diphtheria, and many others, killed millions of people every year.
Even as recently as the early 20th century, cow milk was responsible for approximately
one quarter of all food borne illnesses.
In contrast, today, largely thanks to strict pasteurization processes on commercially sold
milk, only about 3 people die from milk-related sickness per year in the United States.
So how did Pasteur come up with his momentous innovation?
In 1854, Pasteur joined the University of Lille as professor and dean of the science
faculty.
It was here that Pasteur first took up the problem of alcoholic drinks turning sour.
In 1856, after being commissioned by the father of one of his students, M. Bigot, to discover
what was ruining a certain beet root alcohol, Pasteur examined samples under the microscope
and discovered not only spherical yeasts, but also a rod-shaped microorganism, Acetobacter
aceti, which it turns out converts alcohol to acetic acid.
Methodically and systematically experimenting with both lactic and alcoholic fermentation,
Pasteur concluded that fermentation was not the result of a spontaneous generation of
chemical reactions by enzymes (the then-majority view), but rather the work of these microorganisms.
In 1857, Pasteur returned to the École Normale as director of scientific studies and continued
his research on the problem.
Notably, on April 20, 1862, he completed his first test of boiling and then cooling wine
to kill the souring bacteria.
At about this time, Emperor Napoleon III commissioned Pasteur to save the entire French wine industry,
which had become overrun by “diseases” that caused the wine to be sour or bitter.
In about 1863, Pasteur inspected a variety of wineries and came to the conclusion that
“there may not be a single winery in France, whether rich or poor, where some portions
of the wine have not suffered greater or lesser alteration.”
Continuing his research into heating the liquid, Pasteur, who patented his heating and cooling
process in 1865, discovered that the wine could be saved from souring and the original
flavor preserved by heating it to a mere 50-60 degrees Celsius or 122-140 degrees Fahrenheit.
Quickly adopted by the wine industry, the general pasteurization process was not widely
applied to milk until many years later, to the doom of millions.
It should be noted, however, that like nearly every innovation, Louis Pasteur did not discover
this process in a vacuum.
As with almost every apparent giant leap forward, closer examination almost always reveals centuries
of gradual progress and forward steps towards this revelation.
For instance, some historians believe that a process similar to pasteurization may have
existed as far back as 11th century China.
In an attempt to preserve wine, the Chinese would fill hot clay jars with fresh wine,
cover with leaves, seal with mud and, then, bury in the cool soil.
The first documented process of pasteurization (even though it wasn’t called that at the
time) was in 16th century Japan in regards to soy sauce.
In order to ship it to Europe without it spoiling before it got there, the Japanese devised
a process of boiling it in an iron pot, funneling it into bottles and immediately sealing them.
Even immediately prior to Pasture, there were a number of European scientists who helped
pave the path to discovery.
An Italian priest and scientist named Lazzaro Spallanzani realized that “a significant
degree of heat” could be used to kill microbes, then reappearance could be prevented by “hermetically
sealing” the jar (as opposed to cork, “which is very porous”).
Parisian chef Nicolas Appert won a cash prize from the French military for his work in providing
safe, boiled, hermetically-sealed jars of preserved food to the army.
Using the money, he opened the world’s first food bottling factory in 1812, where he canned
and boiled all types of food (including milk).
His method consisted of boiling the glass bottle in much hotter water and for much longer
time that Pasture would later deem necessary.
Due to this, the preserved food would often have its taste altered and the glass bottles
sometimes broke.
A few years later, Englishman Peter Durand devised an iron can with a thin layer of tin
around the exterior that could withstand the boiling process better.
While Spallanzani, Appert and Durand all understand this worked, they didn’t really understand
the nuts and bolts of why.
In 1862, Louis Pasteur answered this question.
While the science behind pasteurization may have been relatively unknown in the mid-19th
century, a basic understanding of biology helps explain it.
Bacteria are single-celled organisms with a cell envelope, the cytoplasm (stuff inside
of the cell like ribosomes, chromosomes, enzymes, etc.) and the flagella (the part that allows
the cells to attach to other things).
When the temperature gets hot enough, the enzymes inside of the cytoplasm chemically
change shape and are no longer able to work properly.
This essentially makes the entire cell unable to function.
Heat can also destroy the cell envelope, which further damages the cells.
Once the offending cells are dead, it is just as important to make sure nothing can enter
back in.
That’s why jars, cans and anything pasteurized needs to be hermetically sealed or refrigerated
(which doesn’t kill cells, but slows their growth) immediately after being heated for
maximal shelf life.
As with other product, the pasteurization process in milk is specifically tweaked to
kill most offending bacteria in the liquid, though to preserve flavor, the milk is typically
not heated high enough to kill all microbes and occasionally post-pasteurization contamination
also occurs.
Since the milk is not hermetically sealed, these microbes still happily feed on things
in the milk and multiply.
Refrigerating it simply slows this process down, but doesn’t prevent it.
When milk goes bad (turns sour), it means that enough bacteria has grown in it to ferment
a certain amount of the lactose, which cause the sour smell.
While slightly spoiled previously pasteurized milk won’t taste good and could make one
sick, the smell usually comes prior to the milk being really harmful and, potentially,
deadly, so this is rarely an issue.
In the century and a half since Pasteur made his discovery, pasteurization of milk and
many other liquids and foods has saved literally many millions of lives, altering human history
since in unknown ways.
Who knows- given the large number of lives saved in the interim, if not for this process,
one of your direct ancestors may not have existed, and hence, neither would you.