Many people assume that sourdough must be more nutritious than regular bread. But is there any science to support that assumption?
A listener writes with questions about sourdough.
I use homemade whole-grain sourdough daily. I am convinced it has exceptional health benefits but I can't find any nutritional info on it. It seems to me that it has to have probiotics, for instance.
With so many people stuck at home over the last year, bread baking in general, and sourdough in particular, have seen a big rise in popularity. And I think many people share this listener's conviction that sourdough must be somehow more nutritious than regular bread. But are these beliefs backed up by any science?
What is sourdough?
Sourdough is a traditional method of making bread that's a bit more time- and labor-intensive than modern methods. (Perhaps that's why we assume it must also be better for us.) A lot of bread these days is made with dried baking yeast, which is reanimated by combining it with warm water. When mixed with flour, the yeast start to digest the sugars in the flour, releasing carbon dioxide gas. This gas gets trapped in pockets in the dough and causes the dough to rise.
Sourdough starter is a living, breathing colony that requires ongoing care.
Sourdough bread also uses micro-organisms to generate the gas that makes bread rise. But in this case, lactobacillus bacteria are doing the heavy lifting. These bacteria, along with some uncultivated (or "wild") yeasts, are naturally present in the flour as well as in the air. To make a sourdough starter, you combine flour and water and let it sit loosely covered for several days in a warm room and let nature do its thing. As the bacteria in the flour start to reproduce, they give off carbon dioxide and lactic acid. Eventually, you end up with a tangy, bubbly mixture with enough oomph to leaven a loaf of bread.
Sourdough bakers will typically take a cup or two of starter out of the batch and then replace it with fresh flour and water. Unlike a packet of dried yeast, which you can store in the fridge for years before using, a sourdough starter is a living, breathing colony that requires ongoing care. If you don't periodically add more flour, the yeast will run out of food and die. (And this is how people end up hiring sourdough babysitters when they go on extended trips.)
What makes sourdough bread unique?
Bread made with sourdough, as opposed to baking yeast, has a characteristically sour or tangy taste that is one of its chief attractions. The texture of the bread is also usually a little denser, moister, and chewier than yeast-risen bread, which adds to its charms. The lactic acid also acts as a natural preservative, meaning that sourdough breads keep well without added preservatives.
Because the specific micro-organisms present in a sourdough depend on the type of flour used and the kind of yeast that happen to live in your kitchen, each batch of sourdough has a unique personality—even a terroir—and one that is constantly evolving. This can be a source of frustration as well as joy.
Talk to a sourdough baker about his starter and you'll soon get the feeling that they are talking about a member of the family (or at least a pet) with a variety of quirky traits and preferences. It's not uncommon for bakers to name their sourdough. An opera-singer friend of mine named his Brunhil-dough, for example.
Really good sourdough starters are valuable. Not like GameStop stock, but still.
If you somehow get lucky and get a really good batch—one that produces a nice springy loaf with the perfect balance of tanginess—you get even more neurotic about it. (Or so I'm told.) Really good sourdough starters are valuable. Not like GameStop stock, but still ... you can divide it and give it as gifts or even sell it.
I was once on a hiking vacation in Wyoming and one day we had breakfast in a diner where the pancakes and breads were made with a famous 100-year-old sourdough starter that had been continuously cultivated since pioneer days. Obviously, we had to buy some of that starter.
For the rest of the vacation, we carted this stuff around in a Tupperware container, carefully keeping it out of drafts and direct sun, occasionally adding flour and water to keep it going. Somehow, we managed to get it all they way home to Maryland without it leaking out in our luggage. Although I'm afraid I no longer have my 100-year-old starter, I did keep ol' Jedediah going for several years before the relationship fizzled out. He was just too needy.
I did keep ol' Jedediah going for several years before the relationship fizzled out. He was just too needy.
In any case, you can see why sourdough lovers might assume that it has "exceptional health benefits"—the same way we just know that our poodle (or 4-year-old) is smarter than the average ninth grader. You can just feel these things.
Is sourdough bread more nutritious than other bread?
Although I'm not sure they rise to the level of "exceptional health benefits," sourdough bread does offer a few advantages. Most of these stem from the lactic acid left over from the bacterial fermentation, and not from the bacteria themselves.
Whatever beneficial bacteria are present in the starter, they will probably be destroyed by cooking. Most lactobacillus bacteria are only viable to about 112 degrees F. So while sourdough starter could be considered a probiotic food, sourdough bread would not.
Although I'm not sure they rise to the level of "exceptional health benefits," sourdough bread does offer a few advantages.
However, the lactic acid may render some of the nutrients in the bread more absorbable and reduce the presence of compounds that sometimes irritate sensitive guts. Although sourdough wheat bread would still be off-limits for those with celiac disease, many people with non-celiac wheat sensitivities find sourdough easier to digest.
Some data suggest that sourdough bread might be less likely to spike your blood sugar than a non-sourdough bread. But at least one recent study found no difference between sourdough and regular bread on average. However, they noted a huge variation in the subjects' blood sugar responses to both sourdough and regular bread. The effect of bread on blood sugar appears to depend more on the individual (and perhaps their microbiome) than it does on the type of bread.
The biggest factor in the nutritional value of sourdough bread is whether it's made with refined or whole-grain flour. Whole grain sourdough will be higher in fiber and certain nutrients than white sourdough. And both maybe slightly more digestible than their non-sourdough counterparts. But regular whole grain bread is usually going to be higher in fiber or nutrients thanwhite sourdough.
Regular whole grain bread is usually going to be higher in fiber or nutrients than white sourdough.
Whole grain sourdough may be one of the healthiest choices in the bread category, but that's not a license to abandon all restraint. Sourdough bread is still bread. Although it may be one of the culinary highlights of your meal, it's unlikely to be the nutritional superstar. You'll still want to consume sourdough in moderation and not at the expense of other more nutrient dense foods.
Is store-bought sourdough healthy?
If you're hoping to get the benefits of sourdough without all the labor involved in tending your own starter and baking your own bread, you can purchase your sourdough ready made. But be aware that a lot of what's sold in supermarkets as sourdough is actually sour-faux.
A lot of what's sold in supermarkets as sourdough is actually sour-faux. True sourdough bread will usually contain just flour, water, and salt.
There's no legal definition for the use of the word sourdough on a label. Breads made with regular yeast may include small amounts of sourdough for flavor but still be leavened primarily with yeast and contain little if any lactic acid. Even more frequently, they'll use vinegar or lemon juice to mimic the sourdough flavor ... without providing any of the benefits.
Check the ingredient list. A true sourdough bread will usually contain just flour, water, and salt. The ingredient list may or may not include the word "starter," "culture," or "levain," as these are also just flour, water, and salt. If it lists yeast, that's a pretty good tip-off that you're not dealing with a true sourdough bread. A long list of chemical preservatives is another clue that it's not the real thing.
If you've been fermenting or baking up a storm lately, post pictures of your favorite starter or the stuff you're making with it on the Nutrition Diva Facebook page!