Having written up the ‘how-to’ of starting a sourdough culture, and the beginnings of a recipe set for it, I was asked about the nature of the sourdough starter. What’s going on in that jar of oozing, smelling, wonderful stuff? How does it work? Is it safe? And why did we stop using sourdough except rarely as a novelty flavor? I found it was time to do some research to answer some of those questions, others I thought I knew, but have you ever known me to pass up a research opportunity? That last is not a question I’m going to attempt to answer in this post, but the others I have every intention of addressing. I never quite know just where to start in posts like this, how much base knowledge to assume. I’d love to hear in the comments what you think.
Why, I was asked, does the sourdough starter begin thick, and thin out as the culture builds in the jar? The quick answer is that the microbial activity in the culture is breaking down the long glutens in the flour, which means that you have something more the consistency of pancake batter or even crepe batter – thin, almost runny. The longer answer, when I dove into articles questioning my own assumptions, is that what’s going on in your sourdough jar is not simply a yeast overgrowth, fostered by warmth, food from the flour you give it, and water for the safe healthy environment a yeast needs. No, it’s much more complex than that.
Broadly speaking, the culture in your sourdough jar has yeast and Lactic Acid Bacteria (LAB). From a microbiologist’s viewpoint, this is like looking at a city and saying ‘oh, there are people living here’ and by people, you mean humans, cats, dogs, budgerigars, and all the myriad other life forms in and among the buildings.
All this activity in your jar! What we think of as sourdough, and use for our own purposes, serves very different purposes to the colony, of course. But we know that the proteins are digested, and science has found that not all of the LAB break down glutens, which means that you could have a culture where that wasn’t happening as much, which would lead to a potentially very different loaf than a culture where this was happening more consistently. Which is, in part, the beauty of sourdough, and it’s downfall.
Commercial yeasts are selected for their efficiency in reproducing, which means there is more gas production, which inflates the springy, stretchy network of gluten proteins that have been hydrated by the water added to the flour. When I make a loaf of bread in my kitchen, even with my stubbornly old-fashioned and mostly unnecessary step of ‘blooming’ the yeast, I can manage a loaf of bread inside two hours. Sourdough is a process of days. The yeasts aren’t bred to reproduce fast, you may have to coax them along a bit, so they simply aren’t as favorable to the baking process – in particular commercially – when speed is necessary. That, and as you may have guessed from the list above, sourdoughs are not consistent in their flavor or results. This could be maddening, or it can be delightfully quirky and individual in a way the hundred loaves of white bread in plastic sacks can never be.
The sour in sourdough isn’t from the yeasts at all. The commensal bacteria culture is responsible for this, and the sourness is responsible also for what makes having a live culture simmering away on your counter safe. The reduced pH of the acid mean that your sourdough is a hostile environment to the kinds of pathogens who would also like to inhabit this nutrient-rich space. This not only means you’re perfectly safe in eating this food that’s been sitting around for days, weeks, even years at room temperature, but it’s good tasting, too. You can trick this flavor – and commercial bakeries totally do – by adding ‘sour’ to a dough. But the origin of sourdough, not only as a food preservative, but a leavening agent that made risen breads possible, is truly an ancient taste. Besides which, how ‘sour’ your starter is will depend on the amount of lactic acid it contains, which relies on the strain of bacterias in it, and that can be highly variable, making your sourdough from a wild start unique to you. It’s very special, and it’s worth the effort, in my opinion, not that I always have the time for a sourdough starter.
The LAB offer something else, beyond protective acid to the starter. They are found to have antifungal properties that persist into the baked bread, meaning that a sourdough leavened loaf could last five days longer than a loaf baked without the sourdough. Commercially baked bread uses added chemicals for this antifungal property. I’ve surprised people unused to fresh homemade bread by cautioning them to eat a loaf I’m giving them within three days, or it will spoil. You can delay this by refrigerating or freezing, but those change the properties of the bread. There’s nothing like a fresh loaf of bread! You can have that longer with sourdough.
Making your own bread is somewhat more common than it was just a few years ago, courtesy of a strange quarantine where you could get foodstuffs, and had youtube to help you learn skills that your parents might never even have known. Still, as life speeds back up to normal again, it would be good to keep this particular skill alive. I don’t anticipate needing to make my own bread, but then again three years ago I’d have looked at you funny if you predicted trips to the grocery would yield empty shelves where the cheap bread used to be… and you’d have been right. This isn’t why I have my starter going. It is why I’ve gone back to having no less than 25lbs of flour in the pantry at all times, and if I can come up with a satisfactory long-term storage of more (yes, I know I could ‘prep’ but frankly that is another post about what’s wrong with that approach) I’ll put aside more. In the meantime, I am going to pamper my DoughBaby, and tinker with recipes to use the discard because I hate waste. It’s safe, it’s tasty, and it’s just so much fun to do this kitchen science when I know what’s going on in that jar!