This video about wild yeast is sponsored by Skillshare. Want to bake some bread but don't
have access to commercial yeast? No problem. You just mix some flour with some water, let
it sit at room temperature and wait for it to grow some yeast all by itself. Yeah, seriously,
it works. It's called making a sourdough starter. There's a million different recipes and procedures
that you can find online that are all very different from each other and they'd all probably
work. I'm going to show you a good procedure right now, but it's important to understand
that scientists don't really know which way of doing this is the best. I mean, bakers
will tell you with a hundred percent certainty that you have to use distilled water or you
have to use organic whole wheat flour, but few of those claims are proven by science.
Indeed, there is shockingly little research about this simple bread making process that
goes back to at least ancient Egypt and I think there's a reason for that.
I've noticed that there's two things that tend to be the focus of food science research
— things with major commercial applications, and things with major public health implications.
And a wild yeast sourdough starter is neither of those two things. It's probably not going
to kill you and it's probably not going to make you rich, so there aren't a lot of research
dollars for it, but that's not stopping the Rob Dunn lab at North Carolina State University
from getting into this. They want you to make sourdough for science. As of this recording,
in the year 2020, researchers are actively recruiting home bakers like you and me to
make a starter using their procedure and then to gather some basic data that can help them
understand just what in blazes is actually going on in here. If you do this, you'll be
adding to the sum of human knowledge and you'll probably make some pretty tasty bread in the
process — or pizza. Managing the Wild Sourdough Project at NC State is Lauren Nichols who
says that they were planning this long before the global pandemic of 2020 created a shortage
of commercial yeast leading to a sudden spike of interest in growing wild yeast. Indeed,
that's the only reason I'm interested. Can't find this at the store anymore.
"We're trying to figure out how where you live and what flour you use affects the rise
and the aroma of the starter you end up with. Common knowledge is that where you are is
going to determine the kind of sourdough you have. So if you're in San Francisco, you're
going to have a very specific starter. And so far what we're seeing from preliminary
data is that isn't true. That specific bacteria shows up in starters all over the world. So
it's not necessarily where you are or necessarily how you keep your starter, but it might actually
be the interactions that are happening between the different microbes in your starter."
This is key to understanding sourdough generally. A normal bread baked with commercial yeast
isn't really defined by its bacterial content. The yeast pretty much do the whole job and
yeast are fungi, not bacteria.
"Basically what they're doing is they're kind of a machine that's breaking down the starches
and the sugars and pooping out these, or farting out actually, these like gases that are creating
the rise of the dough and some aromas that create sort of that, that flavor."
Sounds gross, but without the carbon dioxide created by yeast, bread just wouldn't have
any bubbles in it. And without bubbles, it wouldn't be soft and fluffy. Commercial yeast
is so powerful that it rises a dough with bubbles and just a couple hours — long before
bacteria have had much of a chance to grow inside the dough. In contrast, making a sourdough
starter with wild yeast takes about a week and a half at least, which leaves plenty of
time for bacterial action that will put the sour in sourdough. The first step in this
procedure from NC State is to mix together a couple of tablespoons of flour with a couple
of tablespoons of water in a mason jar or another narrow glass container. The conventional
wisdom among bakers is that you have to use distilled water or water that's gone through
a charcoal filter like the one in my fridge door.
This gets out the chlorine that's used to sterilize tap water and could kill the microbes
you want. It probably depends on what your city water supply is like, but anyway, the
folks at the university recommended dechlorinated water too, just to be safe. If you don't have
a filter, you can just leave tap water standing for a day. The chlorine should evaporate.
Now with the water in, you just cover your starter with something porous like a towel.
The googly eyes are optional, but I'm calling my starter Gary. This will keep big things
like hair from floating into your starter, but it will allow microbes from the air to
pass through and yes, there is yeast in the air. Bakers always used to say that the yeast
are in the air. Then some of them started doing some experiments where they got starters
going inside sealed containers and the starters grew anyway.
This led them to conclude that the yeast and the bacteria are already in the flour, and
indeed, flour definitely does contain yeast and bacteria. Prior research from the Dunn
Lab proves that, but it also proves that there's microbes in sourdoughs that do not come from
the flour. They did a study where they controlled for the microbes already present in the flour
and they still found all kinds of additional and different microbes in sourdoughs baked
by different people in different places. Yeast are ubiquitous in our environment and especially
in our homes. Another study they did involved swabbing the inside and outside of the doors
to people's houses. The inside of the door had way more yeast. There's yeast in the air,
on our tools and on our hands. We do not know the extent to which microbes in the environment
versus microbes in the flour are responsible for sourdough, but we know environmental microbes
do play a role. What those microbes do once they get in the starter is a little bit better
understood.
"Flour is loaded with sugar and starch and everything on the planet can digest sugar
and starch."
This is Dr. Erin McKenney, a microbial ecologist at NC State who's also working on the Wild
Sourdough Project.
"So at first, everything that makes it into that jar is going to do really well."
Indeed, after my starter sat in a warm place in my kitchen for a day or two, it blew up
like a balloon. It looked like it was done.
"But then you have these lactic acid producing bacteria that are actually what we might consider
to be environmental engineers, right? So they're producing acid when they digest all these
sugars and that acid lowers the pH, which selects against a lot of those original fungi,
including some potential mold producers."
And that acid tastes really good. That's the sour in sourdough. There's a battle going
on in the jar between the various microbes and we need to give the desirable bacteria
time to win that battle. Here's one starter I did on day three. It's pink and smells disgusting.
That's an indication that some undesirable microbes are winning. I got kind of freaked
out and threw it down the sink, but the folks at NC State said I probably should have stuck
with it. The acid producing bacteria might have won if given time. And how do you stick
with it? By feeding your starter. There's a really specific procedure that you can follow
on this NC State website, but the basic idea is this. Once a day, you dump and throw away
half of your starter. You then put in enough fresh flour and water to double the mass of
what you have left and to keep it the texture of thick pancake batter.
After you do that for a few days, you should start to notice some clear liquid accumulating
in the jar. Bakers called that hooch. It's literally alcohol created by the yeast and
it's an indication that they are hungry. Once you start getting a lot of hooch after half
a day, that means you can start feeding it twice a day. After about 14 feedings, you
should have a starter that reliably doubles in size between feedings. That means you've
got a vigorous community of yeast and desirable bacteria that can reproduce perpetually as
long as you keep feeding it. If you put it in the fridge at this point, you can get away
with only feeding it about once a week. Cold slows down the metabolic rate. You then use
about half a cup of starter to replace a teaspoon of yeast in a recipe. You just got to account
for all the extra flour and water you're adding to the process and be aware that wild sourdough
usually takes more time to rise — four hours, a day, it depends on the starter.
Now you no doubt have many questions — one of them being, why do I have to throw away
half my starter every single time I feed it? Well, the conventional wisdom is that if you
don't throw away half your starter as you go, you're pretty quickly going to accumulate
way more starter than a home baker could possibly actually need, simply because you have to
double its mass every single time you feed it. It's exponential growth. You can cut down
on this waste by starting with a very small amount of flour and water to begin with. That's
why the NC State recipe calls for just a couple of tablespoons. You probably have to start
with a dough of some minimal size because if it was too little, it would spread really
thin at the bottom of your glass and it would be exposed to too much air. Anyway. Dr. McKenney
says there may be another benefit to discarding half your starter when you feed: It's going
to select for the more powerful yeast.
"Some of them are really good at out-competing other yeasts or bacteria for food. Some of
them might be really good at growing faster, right? That discard process that we do every
day is kind of like mowing your lawn. You select for grass and fast-growing weedy species
and you're not letting many trees or slow growing species grow. Right? So the same kind
of thing is happening in our starters every day. We are a clockwork disturbance force."
OK, another question that I bet you're pondering: What kind of flour do I have to use? Lots
of bakers say you have to use organic because conventional flour has chemicals in it that
will kill the microbes. Lots of people say you have to use whole wheat flour because
the bran and germ contain lots of the microbes and enzymes that we want. Well, "lived experience"
tells us that you can make a sourdough starter out of just about any flour, but some might
work better than others. That's one of the things that the folks at NC State are hoping
you can help them figure out. You'll tell them exactly what kind of flour you used and
simple measurements you take will help quantify how well your starter did. But Nichols and
McKenny already did one experiment where they put the same starter in with some white, wheat
and rye flours, and look what happened.
"All-purpose flour, which has the milling and the processing — there's not a lot of
bran, which would be your fiber source. There's not a lot of germ, which would be your proteins
and lipids. So it is pretty much a starch bomb. And those microbes have a sugar rush
and then a crash. They rise the fastest and then they crash. They can't sustain it, because
they run out of nutrients. But then whole wheat, it's kind of slower, steadier and then
more sustained over time. So it's like your best balanced diet."
This is of course exactly why whole wheat flour is also better for us humans.
"The rye has a lot of sugar because there's amylase — that digestive enzyme that breaks
down starches into sugars. So you see a rapid rise in the rye flour but then you see it
sustained a bit more, because there's still the fiber and the proteins and lipids. Right?
It's like your long distance — your endurance runner."
OK, last thing I bet you're wondering: You're worried that your starter is going to contain
some bacteria or fungus that could make you sick. Well, here's what Nichols says, and
I think this is pretty much what nearly any scientist would say in response to that question.
"Since we're baking bread, you are killing almost everything in it. And so, there's no
health risk there that we know of. But we don't — I'm not going to make any other
claims about sourdough starter itself."
Yeah, she's being careful because she doesn't want to get her university sued. I don't want
to get sued, but I don't think anybody is going out on a limb when they say that cooking
generally kills pathogens in food. People have been baking bread like this for thousands
of years. And when was the last time you read about a major foodborne illness outbreak coming
from sourdough? It is possible that molds could create toxins that wouldn't be destroyed
in the oven. So Dr. McKenney says, don't bake with anything fuzzy that's growing in your
jar. The parts that are most likely to mold are the dry bits around the edge. You want
to try to keep the walls of your container as clean as possible, which I found very hard
to do. But then Nichols slapped me over the head and said, just transfer it to a fresh
container, you ding dong.
Actually she was way nicer than that. But anyway, the link to the Wild Sourdough Project
is down in the description. Follow their recipe, take a few measurements and send them your
data. The instructions are very easy to follow. They especially need bakers from places outside
the U.S. to participate, but they'll take data from anyone. And when you email them
your data, forward it to me at this address (aragusea at gmail). Put "sourdough project"
in the subject line and I will thank you by name in an upcoming video, just as I will
now thank the sponsor of this video: Skillshare. Lauren Nichols and I were talking about how
she went to school to be a scientist, but life has recently taken some weird turns to
where she's now having to be a videographer and a lighting technician and all that. Well,
Skillshare is a place where you can augment your skillset as needed.
It's an online learning community with thousands of classes on things like video photography,
illustration, design. Whether you need to build an app or make a film, there's a class
here for you — a real class, not a haphazard video tutorial. A structured flow — even
homework assignments. Whether you need to make a video or you just need to make your
video chats look better, consider Ryan Booth's DIY Cinematography class. "We'll look at the
light as it kind of falls on the room. We'll talk about how to position our subject and
how best to, kind of, take away a handful of things to make it feel like we've created
this intentional world." Indeed, I have found out the hard way that lighting is just about
the most important thing in any kind of video. Hit my link in the description and the first
thousand of you will get a free two month trial of Skillshare premium. After that, it's
less than $10 a month for an annual membership — a steal compared to most other kinds of
education. Thank you, Skillshare, and thank you for baking sourdough for science. Seriously,
go to the NC State website linked in the description, follow their directions, and if you want,
you can forward me the data that you send them. Put "sourdough project" in the subject
line and I will thank you in a followup video sometime later this year. Now let's bake some
bread with bugs.