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of a website or domain When you think of kombucha,
you might think of a nice, refreshing, healthy drink, one that’s
exceptionally good for your microbiome. But what we here at Journey to the
Microcosmos think of is different from that. Our first thought is of a terrarium… a place where a whole ecosystem
can exist, trapped in glass. Kombucha is an old and mysterious drink. It's thought to have originated
around 221 BCE in Korea and China, though we had a hard time
tracking down the sources for that date. There are also reports of kombucha being
consumed in Russia in the 19th century. But those two time points don’t tell
us much about how kombucha came to be. And that’s not unusual when
it comes to ancient foods. Here on Journey to the Microcosmos, we’ve ventured into the microbial world
of food like bread, yogurt, and cheese. And the processes humans have used to
make these foods go so far back and are accompanied by so much lore that it is
difficult to untangle exact histories. But no matter how murky the history is, the microbial universe buried in
these foods is somewhat consistent. There is an organism, maybe a
yeast or a bacteria or a fungus. It wants to survive, and so it
uses the resources around it— like sugar or the proteins in milk— to do that. It might even work with one or
two other organisms to accomplish its goals. So James, our Master of Microscopes, thought
kombucha was going to be a very familiar sight, something chill like brewers yeast. Or something like the feeling he gets
when looking at fermentation products like yogurt under the microscope, which to him
resemble domesticated animals in a petting zoo. There’s a stable environment and plenty of food. And the organisms within have
no predators and no competitors. But that's not what he saw
when he looked at kombucha. The word that came
to mind then was “wild.” It was so wild that at first he’d thought he
was looking at kombucha that had maybe gone bad, but he quickly realized that
this was not the case. Kombucha is just wild like this. Now if you know anything about how to make
kombucha, then you’ve probably heard about this weird thing that James is pulling
out of the top of his kombucha sample. This is the SCOBY. It’s a strange word, but it stands for something
“Symbiotic Culture Of Bacteria and Yeast”. So yes, that wiggly mass is actually the weird, wild world of bacteria and yeast
that makes kombucha possible. We’re not in the business of giving
recipes here on Journey to the Microcosmos, and besides, everyone has
their own preferences. So we’re just going to describe how
one might go about making a SCOBY. The process starts with some brewed tea, usually black or green, which
is then mixed with some sugar. A bit of some prior kombucha is added to the mix, providing a starter culture
of the bacteria and yeast. Then the container is covered with
something breathable and set aside. Over the next few weeks, bubbles begin
to form on the surface of the mixture, gathering together until they form a thin layer. That layer eventually
thickens into the solid SCOBY. While the liquid used in this fermentation
process will ultimately be too vinegar-y to drink, the SCOBY can be used in subsequent
fermentations with brewed tea and sugar. For those of you who are experienced kombucha
brewers, you might be filling in the gaps of our description with the myriad of choices that
make your kombucha taste the way it tastes, whether that’s the use of store-bought cultures
or the addition of flavorings in later steps. That’s the thing about kombucha: it is all so complicated, and again, wild. The community of bacteria and yeast that
makes up the SCOBY can vary tremendously, depending on where the
kombucha was originally made. And as fermentation progresses, the composition of
the community changes as well, evolving with the culture and responding to microbes in the air
that might try to interact with the kombucha. So this community we’re looking at might
have looked very different a few weeks prior. And the species might not be the exact same
species that make your favorite kombucha. But the underlying processes they engage
in to make that kombucha are the same. When the starter culture is mixed
with the brewed tea and sugar, the yeast use an enzyme called invertase to
break down the sugar into smaller monomers. This kicks off a whole series of
metabolic reactions, beginning with the yeast and bacteria converting those sugar
monomers into ethanol and carbon dioxide. The ethanol could be a problem, as too much
can be toxic for the residents of the mixture. Luckily, the bacteria are able to oxidize the
ethanol, producing acetic acid in the process. At the same time, the bacteria makes cellulose,
which helps form the biofilm of the SCOBY. These interactions demonstrate quite a bit of
cooperation between the bacteria and yeast, and each carries out reactions that
make each other’s survival possible. They might break down sugar or lower
ethanol levels or create the molecules that will help bind the community going forward. These are all examples of cooperation,
and a nice foundation for an ecosystem. For a drink that is as associated with
wholesomeness as kombucha often is, that is a nice image. But ecosystems aren’t marked
solely by cooperation. They’re also marked by competition, as
organisms vie for limited resources and space. There are several ways we might see this
competition taking place in kombucha. For example, not all yeast can
make invertase, that enzyme that kicks everything off by breaking down
sugar for the community to partake in. These non-invertase yeast are considered
“cheaters,” taking advantage of the resources provided by other organisms
without contributing any of their own. But one study of yeast grown with the
bacteria Escherichia coli found that cheater yeast tend to not grow as
well as the yeast with invertase. In an environment where everyone wants sugar, these cheater yeast don’t seem to survive
as well, perhaps because their non-cheating counterparts are able to consume a tiny
bit of the sugar monomers they produce. And that competition between yeasts
might carry over to the kombucha. Earlier, we mentioned that bacteria
oxidize ethanol into acetic acid, lowering the pH of the environment overall. This acid is actually one of several acids found
in kombucha, leading scientists to wonder whether acid in general serves as a protective quality
of the environment, deterring organisms that can’t survive acidic conditions and creating a
gate against invaders that’s made out of that low pH. And there’s another potential shield
against invaders: the SCOBY itself. The thickness of the biofilm acts as a
physical deterrent, further strengthened by its composition, which makes it hard for other
organisms to diffuse their way into the kombucha. Now we should note that these
deterrents aren’t always effective, and sometimes unwelcome organisms
can find their way into the SCOBY— at which point, you should
probably not drink that kombucha. It is this complex array of interactions, some
of which are better understood than others, that makes us think of kombucha like a terrarium— a glass bottle full of an environment you
can watch brewing itself an ecosystem. With every bit of SCOBY that bubbles to
the surface and attaches to each other, we get to see this untamed landscape assemble. And with every SCOBY transferred to a new culture,
we can replicate this small, wild universe. Thank you for coming on this journey with us as
we explore the unseen world that surrounds us. And thank you to Squarespace
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purchase of a website or domain. Let's crack open a cold kombucha to
cheers the people on the screen right now. They are our Patreon patrons. They're the people who make it possible for us
to continue exploring all the weird and wild ways our lives are influenced by tiny, tiny
creatures that we barely even know exist. So thank you to our patrons for
allowing us to continue this journey. If you want to join them, you can
go to Patreon.com/JourneytoMicro. If you want to see more from our
Master of Microscopes, James Weiss, you can check out Jam & Germs on Instagram. And if you want to see more from us, there's
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