Sudeep Agarwala is a program director at Ginkgo Bioworks, a synthetic biology company based in Boston.

Millions of Americans have rediscovered their connection with yeast during the coronavirus pandemic. By some estimates, grocery stores have seen yeast sales increase anywhere from 300 to 600 percent as the entire nation began sheltering in place. Its sold-out status is causing visceral alarm.

As a scientist who studies yeast genetics and who loves baking, I’ve always maintained that the history of human civilization is yoked to our ability to cultivate and manipulate these tiny organisms, and our future is, too.

Luckily, yeast isn’t gone — it’s still all around us.

Maybe it’s best to start at the beginning: What is yeast? As far as we can tell, a few hundred million years ago, a microscopic fungal cell somehow duplicated its own genome. This started the lineage of cells that could eat multiple different sugars and produce carbon dioxide and alcohol as byproducts, killing off any microbial competitors in the vicinity. It’s a powerful tactic: These proto-yeasts conquer the microbial world, finding harbor on practically every fruit, grain or sugar-rich surface available to them. They evolved and adapted to their local niches until humans decided to exploit the power of these alcohol-producing, carbon-dioxide-belching microbes to brew and bake. Voila, our mighty bakers’ yeast: Saccharomyces cerevisiae.

Wild yeast really is everywhere, and you can harvest and propagate it at home. Scour your cupboards for old dried fruit (raisins, apricots, prunes) and add them to a few tablespoons of water. As you mix everything around, you’ll notice the water getting slightly cloudy — that’s your yeast. But it needs something to eat. Add an equal amount of flour to form a loose paste, and store it in a warm corner of your kitchen until you see bubbles: That’s your yeast waking up and starting to grow. Within 24 hours, there should be a healthy, vigorous soupy mix — your very own wild yeast and bacterial culture, ready to be transformed into your favorite bread!

Nurturing this culture is a hobby in itself: I find taking small portions of the living dough and diluting it into equal parts flour and water oddly relaxing; fretting over the health or vigor of my starter is a useful way to pass the long hours spent sheltered at home. My starter rewards me generously by bringing all my baking projects to life. Yours will, too; tending to the puddle of flour and water in a jar on your kitchen counter, folding dough and baking bread — it somehow works comfortably into a new pattern of daily life, a comfort at a time when our usual patterns have been disrupted by a pandemic.

Of course, the experiment you are doing with the dried fruit in your cupboards is the same one humans have been doing from time immemorial. Our earliest evidence of beer-brewing with yeast comes from the Near East almost 10,000 years ago. In the Epic of Gilgamesh, written in the second millennium B.C., the wildman Enkidu becomes civilized only after he eats bread and becomes drunk on beer. And yeast is still at the heart of our civilization in the 21st century. In biomedical research, we have used yeast as a model to understand what happens when our bodies manifest cancer, or what changes in a cell when we develop myriad diseases.

In my current role as a biological engineer, I view yeast as a canvas for creativity. I think about the future of food as we know it: How can we develop yeast to produce components in our food chain that are otherwise resource-intensive or unsustainable? Other companies have made major contributions to human health, developing yeast to produce antimalarials such as artemisinic acid, or life-saving proteins including insulin.

Although yeast shapes how we understand the world and how we will live in the future, I still maintain that its most visceral connection is to bread and fermentation. It is yeast that provides the nooks and crannies in our English muffins, that slowly swells the loaves we proof on our countertops while sheltering in place. Yeast will make hot cross buns rise at Easter.

And its absence marks a time of sorrow or concern: In less than a week, Jews around the world will commemorate Passover, the rushed escape from Egypt, by eating matzoh, the unleavened Bread of Affliction. Millions of Americans are feeling this now as they wander down empty baking aisles.

Especially now, any yeast we find will be a source of celebration and reprieve from an exhausting news cycle and our constant anxiety. Our leaven gives us levity in our bread, effervescence in our beer, sparkle in our champagne — all we need do is reach out and cultivate it.

Catching yeast at home
30g (roughly 1 heaping tablespoon) dried fruit (raisins, apricots, dates, cherries)
40g (roughly 3 or 4 tablespoons) drinking water
40g (roughly 4 or 5 tablespoons) white flour (wheat or rye flour produce more vigorous results)
1. Combine fruit and water in a jar or bowl. Stir fruit around to release some of the yeast.
2. Add flour to the mixture and stir to create a thick paste
3. Cover the container loosely so nothing can fall in, and store in a warm (not hot) part of your kitchen: Above the refrigerator or in the oven with the light on work great.
4. Allow the mixture to sit for 24 to 48 hours, depending on the temperature of your kitchen. Small bubbles should form in the first 12 hours; these should grow considerably as you let the mixture sit.
5. To cut back, take ½ teaspoon of the bubbly mixture, and add it to a new container with roughly 40g water and 40g flour and let it sit until bubbly again. You don’t need to transfer any fruit at this point. Repeat this step three or four times before your first bake with your starter. Always use newly cut-back, vigorous starter for your baking.
Notes: This method is incredibly versatile. Don’t have dried fruit? Try it with some fresh grapes or plums you have around. Short of that, try any dal you have (chana, urad or masoor work well). Or try boiling cut potatoes in some water, let the water cool, and mix it with an equal part flour. In a pinch, just mixing equal parts water and flour, or equal parts water with rye flour will work too. This will take much longer but should produce active starters.
Don’t have flour? Try using other sources: fine cornmeal or semolina flour. Or, blend some oats to replace the flour. You can try experimenting with any number of things here.
Safety: Young starters — before the yeast can really get its footing — are the most vulnerable to infection by the wrong sort of bacteria, including possibly E. coli. A pinkish or orange-ish tint may indicate bad bacteria. Discard and start again if you see this color change, or mold.
Sudeep Agarwala, 2020

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