The Reason Sourdough Bread Takes So Long To Go Stale

If you love to sink your teeth into a great slice of bread, chances are your bread box contents range beyond plain ol' sliced wheat, white, and cinnamon raisin to include heartier varieties such as rye, pumpernickel, and, of course, sourdough. Although sourdough bread soared to new levels of trendiness during the COVID-19 pandemic, when many cooks staying at home decided to try their hands at the baking technique, NPR explains that it's actually the most ancient method of preparing leavened bread, dating back at least as far as ancient Egypt.

If you've never made the hearty, tangy, typically robustly-crusted bread at home, then you might not know that sourdough is actually sour due to the natural fermentation process that creates it. And as it turns out, that same fermentation process is the one responsible for sourdough's long shelf life when compared with unfermented, commercial types of other loaves of bread.

If you like to keep sourdough on hand — whether homemade or storebought — then you may have noticed it seems to stay fresh for an extraordinarily long time. Sure, you might have to cut away a thin slice where the exposed bread has hardened, but often, after doing so, you'll notice that the bread within is still fresh. According to Consumer Reports, true sourdough indeed has a longer shelf life than packaged bread, which doesn't go through a fermentation process. And that's because, the outlet explains, of the natural acids present in sourdough, which keeps mold at bay.

The site writes that the bacteria and yeasts that sourdough doughs incorporate from the flour and air as they ferment pre-baking produce acids and other compounds, which leaven the bread and also lend it its distinctive tang. Those acids are naturally antifungal and antibacterial, which is the reason why properly maintained sourdough starters (the flour-and-water slurries used to make sourdough) can last for centuries. The Italian chef and cookbook author Sara Papa, for example, claims to bake her loaves from a Milanese starter dating to 1848 (via BBC). Those acids stay intact after baking, Consumer Reports notes, warding off mold and keeping the bread from staling. So the next time you buy or bake a loaf, plan to have it on hand for a while — if you can resist polishing off the fresh bread in one sitting, that is.