The Science of Alcohol: From Beer to Bourbon


For humans, food and drink are more than just
a necessity for survival. They’re a huge part of our culture and our
history, shaping our lives on a daily basis. And alcohol has had perhaps the strongest,
uh, influence on us. Pun intended. From soft alcohols like beers and wines to
hard liquors like whiskey and vodka, booze comes in many shapes and styles, and can be
found all over the world. But how did humans discover alcohol, and how
is it made? Thanks to some microscopic organisms, some
time, and some crafty chemistry, we’ve gotten pretty good at our creating our own hooch! The alcohol we’re describing today is ethanol,
which is actually just one type of alcohol. But it’s the only one that’s safe to drink
in large quantities, because we’ve developed the ability to metabolize, or break down and
eliminate its toxic components. Ethanol occurs in nature thanks to fermentation
— the process of breaking sugars down into ethanol and carbon dioxide. And humans — and our non-human ancestors
— have been able to metabolize that ethanol for a really long time. From examining our DNA, some scientists estimate
that our ancestors developed the ability to metabolize ethanol around 10 million years
ago — way before we were mixing our own cocktails. Back then, we hadn’t even split off from
the ancestors of chimpanzees. But that adaptation could have been helpful
for our early primate ancestors by allowing them to eat fermented fruit without getting
sick. Evolving humans must have enjoyed what they
felt when they ate fermented fruits, because figuring out how to create our own fermented
beverages quickly became a centerpiece of human culture. In fact, there are some researchers who believe
that our desire for alcohol is what drove us to develop agriculture, which would have
given us constant access to the grains and starches needed to produce our own booze. The earliest known evidence of the deliberate
creation of an alcoholic beverage is 9,000 years old, discovered in some pottery in the
Yellow River Valley in China. This drink was some sort of wine, and contained
rice, honey, and grapes. In 2005, researchers actually recreated the
drink based on a chemical analysis, and apparently it tasted, quote, “very intriguing.” Archaeologists think that around the same
time people were originally making this stuff, barley beers and grape wines were being produced
in the Middle East. People probably made those early drinks by
leaving fruits and grains in covered containers for long periods of time. Eventually, they’d open the containers,
and the liquid inside would be alcoholic — but for thousands of years, no one knew exactly
why this was happening. Thanks to modern science, we’ve got it pretty
much figured out. Beers are produced by fermentation, which
comes from the Latin fervere, meaning “to boil.” Which makes sense, because the mixture of
grains and water does bubble during the process. And a beer really only needs four basic components:
grain, water, yeast, and hops. Different varieties of these components mixed
in different ratios can give each beer a distinct flavor. There are also different ways to do the beer-brewing
itself. But here’s how the process generally works: The first step in making beer involves cooking
grains in water, which produces a mix called the mash. The heat activates enzymes within the grains
and begins to break the starches down into simple sugars. Different grains are used for different kinds
of beer; dark roasted grains are used for darker, heavier beers like stouts while light
grains are used for light beers, like wits and pilsners. Once they’ve all been cooked down, the grains
are removed from the pot and the remaining liquid is boiled. At this point, the liquid is called the wort,
and it’s during this step that the primary flavoring element of the beer is added — hops. Hops are actually flowers, harvested from
a climbing vine called Humulus lupulus. Beers have always been flavored with herbal
mixtures, and we’re not sure when or why hops became the herb of choice — but it was
first noted as being part of brewing sometime in the ninth century CE. Adding hops to beer helped balance the sweet
flavors from the grains with an acidic kick, but more importantly, the hops kept it from
spoiling, so the beer lasted longer. We now know that hops produce antibacterial
compounds called alpha and beta acids, which help keep the beer free of bacteria and support
the growth and survival of the yeast. These acids mainly give the beer its distinctive
bitterness, but different varieties of hops can also give beers citrusy, floral, and even
piney notes. After the boil, the liquid is rapidly cooled
to prevent bacterial contamination and oxidation, which can change the taste of the beer. Once the wort is cooled, the yeast is added
to begin the fermentation process. Yeast — in this case, a particular variety
called Saccharomyces cerevisiae — is a microscopic, single-celled fungus. Yeast rely on sugars for energy, so they eat
up the sugars in the wort and spit out carbon dioxide and ethanol as waste products. The carbon dioxide is why the liquid bubbles,
and the ethanol is why there’s alcohol in beer. During the first phase — the primary fermentation
— there’s a lot of yeast hard at work. All that waste carbon dioxide is allowed to
escape the container, while the ethanol is left behind. After a while — usually a minimum of two
weeks — most of the sugar has been consumed and most of the yeast is dead. In some cases, the beer is transferred to
bottles with a small amount of sugar, to help fuel the remaining yeast through the last
step: secondary fermentation. The beer is then tightly capped, and the carbon
dioxide and ethanol produced within the container are preserved, finally turning the liquid
inside into the fizzy, intoxicating beverage so many of us love. Wine production is similar to beer-making
in a lot of ways. It’s just that, instead of grains, wines
use fruit to produce alcohol. And as you probably know if you’ve ever
tasted a $3 bottle of wine, different varieties of grapes, and how they’re prepared, can
dramatically affect the flavor of the wine. First, the grapes are crushed. Back in the
day, people used to stomp on the grapes in big tubs, but now it’s generally done with
specialized mechanical crushers. The resulting mixture of skins, pulp, and
juices is called the must. Whether the wine is a red or a white usually
depends on this step. White wines are often made from green grapes,
and red wines are generally made from purple grapes — but the color of the grape doesn’t
automatically determine what type of wine it will be. In fact, purple grapes can be used to produce
both kinds of wine. Leaving the dark grape skins sitting in the
must will lead to a red wine, while separating the juices from the skins and pulp quickly
will lead to a white wine. Those dark grape skins also contain tannins
— compounds that a chemist would call polyphenols. They’re made of lots of connected rings
of carbons attached to an oxygen and a hydrogen. These compounds give red wine its characteristic
dryness, and help red wines age well, smoothing and mellowing the flavor over time. As with beer, the key component in turning
the grapes into wine is the presence of yeast. In the old days, naturally-occurring wild
yeast on the grapes, mashed into the must by winemakers’ feet, would kickstart the
process. These days, winemakers sterilize the must
and add their own specially-selected yeast for better control over the wine’s flavor. Just like with beer, the yeast converts the
grape’s sugars into ethanol and carbon dioxide. After fermentation, the yeast is killed off
or filtered out and the liquid is clarified to remove particles that might affect the
taste or appearance of the wine. The wine may then be aged in wooden barrels
for a few months to a few years, which gives the drink more flavors. Finally, it’s bottled and shipped off for
consumption, ready to be sipped by vinophiles everywhere. So those soft alcohols, as it turns out, are
pretty easy to make by mistake – but what if you want throw a really crazy party? How do we make hard liquor? High-alcohol-content beverages like vodka
and whiskey require an additional step: distillation. Distillation is a process of deliberate evaporation,
cooling, and condensation that produces purified liquids. Creating hard liquors this way takes advantage
of the fact that ethanol has a lower boiling point than water, so i t turns into a gas
at a lower temperature than water does. Just like with beer and wine, hard liquors
begin with a fermentation step. Different fruits, grains, and starches can
be used to create this initial brew, depending on the liquor. For example, potatoes are generally used for
vodka, while bourbon is made from corn, rum comes from sugar cane, and tequila is made
from agave. The yeast gobbles up all of those sugars and
produces ethanol and carbon dioxide, but the liquid has a relatively low alcohol content
— around 10-15%. So, to make the liquor truly hard, we have
to purify some of that liquid to give it a higher alcohol content. The liquid is transferred to the still, where
it’s heated inside the pot until the components with lower boiling points begin to boil off. As the solution vaporizes, the temperature
is increased very slowly, pushing other compounds to boil at the appropriate temperatures. The boiled–off vapor rises to the top of
the pot and passes into the distillation column, where specialized plates cool the vapor and
cause it to condense and drop back into the pot. This gives distillers precise control over
the spirits as they pass up through the column, allowing them to make adjustments to the contents
and flavor of the drink. The compounds with the lowest boiling point
are able reach the top of the column and pass into the lyne arm, a horizontal pipe that
condenses the vapor back into liquid so it can be collected. This distillate is collected in stages, with
each stage kept separated by its boiling points. The first portion of the distillate, called
the heads, contains the most volatile compounds – the liquids with the lowest boiling point. These include acetone and esters, and small
amounts of these compounds are saved to add flavor to the final product. The second portion of the distillate is called
the heart, and it’s the most important part, because it contains all of that intoxicating
ethanol. The heart is collected, mixed with some of
the heads, and usually further modified until it reaches the desired flavor profile. Which … sounds really strange out of context. Some of these modifications involve flavoring
the liquid directly, like by adding juniper berries to gin. They can also involve redistillation — passing
the distillate through the process all over again. And of course, hard liquors can be modified
through aging. Like wine, the type of container a spirit
is aged in can have a significant effect on its behavior. Bourbon is aged in newly cut and freshly-charred
oak barrels, imparting a rich, smoky flavor to the drink. Scotch, on the other hand, is aged in used
barrels — usually in barrels that have been previously used for aging bourbon or sherry. Different varieties of the same kind of spirit
can age for different amounts of time, too – like how white, or blanco tequila isn’t
aged, but reposado, or rested tequilas have been aged in oak for at least two months. So there are a lot of ways to turn that distilled
ethanol into the many different kinds of liquors available around the world. Scientists are working in breweries and distilleries
every day to combine these scientific techniques in new and interesting ways, creating super-bitter
beers and unusual kinds of liquors. And all of these beverages are a part our
culture and our history, from the earliest beers to the latest development in distillation
technology. Thanks for watching this episode of SciShow,
which was brought to you by our patrons on Patreon. If you want to help support this
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