Baking sourdough bread has become a cliché of non-essential privilege in the social isolation era. It’s a time-consuming stay-at-home endeavour that somehow every blogger on my news feed has decided to post about, and I’ve mocked it. But after baking a loaf based solely on advice from a viral tweet and its tweeter, I realise that maybe these bakers are doing something right. After all, they’re the ones enjoying the fresh-baked bread, and the process wasn’t as difficult as I thought it would be.
If you’ve visited a grocery store in any large city, you’ve likely found some missing staples as our doomsday prepper instincts kick in—no toilet paper, no soap and curiously, no yeast. Last month, a tweet thread by biologist and self-proclaimed viking Sudeep Agarwala went viral scoffing at such a predicament—”THERE IS NEVER A SHORTAGE OF YEAST,” he tweet-shouted. If you have some dried fruit, flour (also impossible to find in many supermarkets these days, but let’s forget that for the purposes of this story since you won’t be baking bread without it anyway) and water, you’ve got all the yeast you need.
Friends, I learned last night over Zoom drinks that ya'll're baking so much that there's a shortage of yeast?! I, your local frumpy yeast geneticist have come here to tell you this: THERE IS NEVER A SHORTAGE OF YEAST. Here's where I'm a viking. Instructions below.— shoelaces3 (@shoelaces3) March 29, 2020
As a biologist at the well-known synthetic biology company Ginkgo Bioworks, Agarwala had the authority to make such a claim. And I’m a sucker for low-effort kitchen projects. So, I wondered: if there really wasn’t any packaged yeast left, could I create a delicious loaf of bread with a sourdough starter I grew based on a tweet alone?
Before we start, I should tell you that I’m not a total neophyte when it comes to kitchen experiments. I’ve long had an interest in food science, and I have written about fermentation, gluten and molecular gastronomy. I’ll occasionally experiment with pickling or weird chemicals in my own kitchen. But growing and raising yeast is something I’ve never done before—in fact, I’ve only baked with yeast three times in my life, always with the packaged active dry stuff, and one of those times yielded a loaf so bad that I had to throw it away.
Take your fruit (or, if using fresh fruit skins–please use your judgmenet), pop it into a jar, and add a little bit of water to it. 2 or 3 tablespoons (30-40 mL) is more than enough. If you stir the fruit around, you'll notice the water gets slightly cloudy. That's the yeast!— shoelaces3 (@shoelaces3) March 29, 2020
I found a container—a Solo cup, a signifier of how seriously I was planning on taking this endeavour—and went to work, following Agarwala’s instructions. I mixed some ancient raisins I found in the cupboard with two tablespoons of water and stirred. The water did not get cloudy as it was supposed to, but I forged onward. I added the same amount of flour (by mass) as I had water, stirred, and put the cup in the sun to warm. I figured the process would be done in a day and I’d be baking by the end of the week.
Why did I choose raisins? “There’s yeast in wheat, so you can mix it with water and a week later you’ll get something. But I’m not a patient man,” Agarwala told me. “What’s lovely about adding raisins is that you’re adding a source of sugar to the starter and spiking it with a little bit of yeast.” He said that this system had grown him a usable starter in 24 to 48 hours.
It took me several weeks. But we’ll get back to that.
It’s true that yeasts are everywhere—they’re actually a vast group of single-celled organisms in the fungus kingdom. Our relationship with yeast’s fermentation process probably started via beer brewing: Wild yeast cells from the surrounding environment ate the carbohydrates in a grain infusion, releasing carbon dioxide to produce bubbles and alcohol that prevented more dangerous microorganisms from growing. At some point, ancient flatbread bakers probably noticed that their dough was bubbling from yeast eating the sugars in the flour, causing the dough to rise and change the bread’s texture.
Today, we’ve tamed yeast to the point that you can buy it in stores and mostly expect it to do your bidding in a matter of a few hours, exploiting its fermenting behaviour to leaven your bread. The expelled carbon dioxide produces bubbles in the dough that are held in place by the network of gluten proteins in the flour. Baking the dough locks the bubbles in place and also induces the browning, or Maillard reaction, that gives the bread a flavorful exterior crust. You can still get these effects from wild yeast—it just takes longer, and you have to do the taming yourself.
A day after first mixing the raisins, flour, and water, I looked into the Solo cup—it had produced a single bubble. Proud of my progress, I took some of the flour-water-raisin paste, mixed in more flour and water, and waited. After two days, the mixture formed a brown liquid with a crust on top, but no new bubbles. I took this to mean that I was doing something wrong. (More likely, the raisins were washed at some point, and I was not patient enough to let yeast from elsewhere infiltrate the paste.)
Determined to grow a yeast-powered monster of my own, I started over, now with a bread crust instead of raisins. I fed the yeast beast daily, discarding all but some of the paste and adding an equal amount of flour and water. I learned from A.A. Newton that could keep my starter in the microwave with a bowl of hot water to give it the welcoming environment it needed to thrive. The Solo cup smelled a bit like vomit, but a quick Google search told me that vomit isn’t such a bad smell during the first few days of your sourdough starter. It also grew a crust on top each night, which I eventually learned was because I’d been leaving it uncovered. And after a few days continuing this way, my starter began to thrive—it wasn’t foamy yet, but at least there were actually visible bubbles.
With April holidays fast approaching, I pressed on, knowing that my new hobby represented the exact antithesis of a holiday during which I’d be forbidden from eating leavened bread for eight days. I hoped to raise the yeast through the holiday, and when it was over, have a large and active-enough starter that I could bake a loaf the night the holiday ended.
But then, disaster struck: My beautiful baby starter stopped bubbling.
Sourdough starters are kind of like “a brutal microscopic eugenics program,” as Seamus Blackley, creator of the XBox and also a bread baker, once tweeted. As the overlord of the sourdough starter, it’s your job to produce an environment where the yeast cells beat out all of their tiny competitors. By discarding some of the starter, mixing it with flour and water, letting it sit, discarding some, mixing in flour, letting it sit, et cetera, you’re amplifying the yeast in the mixture each time. Meanwhile, another friendly microorganism—a bacteria called lactobacillus—produces lactic acid through its own fermentation process that ultimately lends sourdough its titular flavour. You must continue maintaining the proper environment to get the microorganisms to do what you want.
It’s unclear what happened to my starter. I thought that maybe I killed it by cooking food beneath the microwave where I’d been storing the yeast, making the starter too hot. Agarwala speculated that the temperature didn’t kill it, but that perhaps the environment had caused the yeast to eat all of the sugar and resort to consuming the alcohol byproduct instead, slowing its bubbling.
Regardless, I was not giving up easily. While rinsing some brown rice before cooking it, I noticed that the runoff was cloudy. Huh, I thought, I should just pour some of this into the bubble-less starter. Within two days, my starter had regenerated. Each new morning, I woke up to a fluffy paste that looked exactly like the sourdough starters I’d seen at friends’ houses or online. It was finally time to bake the bread.
During all of this, I tried my best to make the process as unscientific as possible. Sure, you can treat bread as a science, but I was just trying to think like a regular person who wanted to bake based on a viral tweet. So, for the bread recipe, I once again put blind faith in Agarwala—this time securing said advice on the phone—asking him to suggest a recipe. Then I embarked on the baking process, which itself spanned three days.
First, I mixed 20 grams of my starter with 150 grams of water and 200 grams of a flour mixture that was three parts all-purpose, one part whole wheat. I let the creature sit in its now permanent microwave home overnight. The next morning, I mixed 600 more grams of that flour mixture with 400 grams of water and let it sit for a half hour. This is the autolyse step; the pause allows the enzymes in the flour to break down the proteins so that gluten protein network can form more easily, and turn some of the flour’s starch to sugar for a yeast feast. Then I mixed in the microwave gremlin, added 15 grams of salt (which is for flavour and for strengthening the gluten protein network, I learned), gently kneaded the sticky mass every few hours, and put the dough into the fridge overnight to really let the flavour develop.
After a sleepless night in anticipation of my bake, I set the oven as hot as it could go, popped in a cast iron skillet, and then put a smaller skillet filled with ice cubes beneath it. The ice generates steam to produce a really moist oven environment. This slows the development of the crust and allows the bread to rise even more—which is incidentally why people bake in Dutch ovens, but I don’t have a Dutch oven. Then I sliced the top of the bread with a knife, put it on a floured piece of parchment paper and into the top skillet, lowered the oven to 450 degrees Fahrenheit, and baked for 20 minutes. After that, I took the smaller skillet out, let the bread bake for 20 more minutes, removed it from the oven and let it cool for an hour.
How was it? Folks, it wasn’t perfect, but it tasted damn good. The bread definitely had a crust, it rose, and it was as sour as a loaf you might buy at a famous San Francisco bakery. Obviously some things went wrong—the crust wasn’t quite as crusty as it could have been, I’m sure it could have risen more, and I had a blowout—basically, the gas couldn’t escape through the cuts in the top of the loaf, so it just burst out of the sides. Perhaps my cuts weren’t deep enough, or there was some other issue with heating. But I don’t care: I did it, and now I have a loaf of bread I really enjoy.
I learned a few things from this endeavour: First, baking sourdough bread is highly scientific; mixing chemistry and biology is a huge experiment with many variables that meticulous bakers must control in order to make the perfect loaf. Second, I learned that sourdough bread is a chaotic, seemingly impossible-to-control monster where things sort of just happen and you fly by the seat of your pants and Google searches and cross your fingers hoping that this thing you wasted several pounds of flour on won’t be a disaster. Things go wrong throughout, and you just keep going.
But most importantly, I learned that yes, if the world ran out of packaged yeast, I could make a dank loaf of bread from knowledge I gleaned from viral tweet. It would probably still take a long time, but it wouldn’t be quite as difficult as I thought it would be.