Its catapult to popularity may have been triggered by the pandemic-induced yeast shortages, but even months later, when instant yeast is once again available at most grocery stores, sourdough鈥檚 contemporary stardom is barely starting to fade. Sure, many of us turned to making a sourdough starter to simultaneously combat yeast scarcity and our newfound fear of going to the grocery store. But lots of us have kept up with our strange new hobby of mixing water with flour and leaving it on the counter for reasons beyond just the practical.
Taking care of a sourdough starter takes time, especially when it鈥檚 first coming to life, and we have lots of it now. If you had asked me to add a new daily task to my routine 7 months ago, I think I鈥檇 have answered with a big sigh and a polite 鈥渘o thank you鈥�. But now, amid a global pandemic, when time seems to simultaneously move lightning-fast and terrifically slow, taking a few minutes a day to care for a little jar of microbes seems like a great idea to me.
North Carolina State University professor led that saw 560 samples of sourdough starters from around the world sent to and analyzed by his lab. They found tremendous variation in what species of microbes inhabited sourdough starters, but they also found that people treated their starters as so much more than just ingredients. 鈥淧eople talked about them like they were pets,鈥� , 鈥淢ost starters had names鈥�.
Personally, I named my starter ReeRee. I made her from scratch with just flour and water by following . She lives in a mason jar covered by a cloth, and now that I鈥檝e returned to my usual schedule of going to the lab every day and don鈥檛 have time to bake bread so often, she lives in the fridge. She gets one meal a week of 50 grams of white flour, 50 grams of whole wheat flour and 100 grams of water.
If you don鈥檛 have a sourdough starter of your own, the personification of our lumps of gluten can seem pretty strange. But once you dig a bit into the science of sourdough, and what that lump is actually made of, treating it like a pet starts to make more and more sense. After all, a sourdough starter is essentially a colony of microbes.
While most breads are baked using yeast (specifically bakers鈥� yeast, S. cerevisiae), sourdough starters contain more bacteria than yeast, sometimes up to . are overwhelmingly dominant in starters, and accordingly, it鈥檚 mostly lactic acid that makes a sourdough starter sour!
There are some fungi in most starters, but they鈥檙e different species than bakers鈥� yeast. They have to be since they need to be tolerant of extremely acidic conditions (a sourdough starters鈥� pH can anywhere from ).
Just like bakers鈥� yeast, the microbes in sourdough starters consume sugars from the flour and produce carbon dioxide gas. This gas becomes trapped in the dough, forming little bubbles and producing the airy bread texture we know and love. But where do these CO颅2-producing machines come from?
A better question may be where don鈥檛 they come from. It seems that almost every process of making and maintaining a sourdough starter contributes some microbes to the mix. Some bacteria and fungi come from the flour itself, some from the water, some from the air in our home, and many from our hands when we knead the dough. Because no microbes are purposefully added, the process of a starter coming to life is called spontaneous fermentation.
With such a wide variety of potential microorganism-sources, it鈥檚 easy to see why sourdough starters can vary so wildly. Even though most of the bacteria that thrive in a starter are lactic acid-producing, that only narrows it down to several hundred different species. The previously mentioned led by Rob Dunn found several hundred different species of both yeast and lactic acid-producing bacteria in starters around the world.
It also found that certain microbes were confined to certain parts of the world, giving credence to the idea that sourdoughs from different places truly do taste different. But even within a certain region or country, no two sourdough starters are liable to be exactly the same. The type of flour, where that wheat was grown, the history of the soil, the type of water, the microbes present on the baker鈥檚 hands and in their kitchens, all change the delicate balance of the sourdough starter colony.
Rob Dunn鈥檚 lab did where they sent 15 different bakers in different homes identical sourdough starter ingredients and instructions, and after several weeks characterized the microbes present. The starters all had some species of bacteria and fungi in common, specifically the ones that were also found in the flour itself. However, they all also had microbes unique to each starter. In an attempt to help solve the case of the spontaneous fermentation, the researchers swabbed the 15 baker鈥檚 hands, and found some really interesting results!
Many of the microbes present in the starters but not in the flour indeed seemed to have come from the bakers鈥� hands. More interesting, however, were the microbes that appeared to have jumped not from the bakers鈥� hands to the starter, but vice-versa! While that Lactobacillus made up between 2 and 8% of the bacteria on human hands, the bacteria on the hands of these bakers were on average (and up to 80% in one case). Similarly, almost all of the fungi on their hands common in sourdough starters.
It seems that even while our sourdough starters are colonized by the microbes in our environments and on our bodies, the inverse is true as well. If you鈥檙e worried about getting sourdough starter microbes on you when baking bread, you shouldn鈥檛 be. For one, the vast majority of bacteria and fungi found in starters are non-pathogenic. But more importantly, you are already covered in billions of microbes of your own!
As Rob Dunn explained, 鈥淚f you sample the microbes on someone鈥檚 hands, have them wash them, and then sample the microbes again, no change in the overall composition of the microbes occurs.鈥� We are covered in so many microbes that washing our hands can鈥檛 even meaningfully impact the population, so I highly doubt that a few more or less from your sourdough starter will make any impact. Though I guess you could always wear gloves.
Whether you make it yourself or buy it at a bakery, sourdough bread is undeniably unique tasting and delicious. But did you know that it may also spoil slower than bread made with bakers鈥� yeast? Research has that the bacteria in a sourdough starter produce a variety of chemicals (such as various organic acids and hydrogen peroxide) that can inhibit the growth of other microorganisms like moulds.
I tested the preservation power of sourdough bread for myself, by baking two loaves of bread (one made with ReeRee, one made with bakers鈥� yeast) and leaving a slice of each in a container in my kitchen. The conventionally made bread showed its first spot of mould after three days, and while it didn鈥檛 take the sourdough bread much longer to mould, only about 24 hours longer actually, the sourdough did last slightly longer. This is obviously far from a properly designed and controlled study, but if you鈥檙e looking for something to do while at home in quarantine, why not try it out for yourself! I鈥檝e included photos of my loaves when I made them and three days later.
As if you needed more reason to switch to sourdough bread, studies have also shown that it , and it may even like , magnesium and zinc, although it doesn鈥檛 seem like this last assertion has been tested in humans yet.
If you don鈥檛 have a sourdough starter of your very own yet, doubles as a handy guide, and a citizen science project from the Rob Dunn lab that you can take part in! Just follow the instructions to make your own starter, and report on its characteristics in the linked webform. If you鈥檙e feeling really ambitious, you can even create more than one starter to compare either different types of flour, or what happens if you keep your starter inside or outside. Personally, I think I鈥檒l be making ReeRee a friend, all in the name of science of course.
