Lower Glycemic Index
The glycemic index (GI) is a value assigned to foods (ranked on a scale of 1 to 100) based on how slowly or how quickly those foods cause increases in blood glucose levels.
Many modern bread products, especially white bread and highly processed bread, produce a high glycemic response (a quick spike in blood sugar) as the starches are quickly digested.
In sourdough, the fermentation process appears to lowers the GI of bread.
During fermentation the yeast and bacteria in the culture consume some of the starches and sugars in the flour, but it also appears that the acids produced during the fermentation process slows down the rate at which glucose enters the bloodstream. Further, a 2009 study from the University of Guelph suggested not only that naturally fermented bread had lower GI than whole-wheat bread made with commercial yeast, but also that the body’s glycemic response remained lower hours later.
Complex flavor development and robust texture
The metabolic by-products of various microbes is what is the key to the transformation of flour into bread.
Carbon dioxide produced by yeast and bacteria leaven (rise) the bread, while ethanol excreted by the yeasts contribute to aromas. The acids produced by the bacteria have a whole range of crucial effects. They contribute to flavor, strengthen the dough and as discussed earlier, increase the digestibility of grains. There is a fifth powerful flavor category the Japanese call umami (besides sweet, sour, salt and bitter) and natural fermentation is one way to bring out a broad range of umami flavors.
Lactobacilli bacteria outnumber yeasts in sourdough by as many as 100 to one, and it is the acid produced by these bacteria that produce aromatic compounds that infuses the bread with flavor, i.e. the flavors in bread are created by the microorganisms that ferment the flour, not the flour itself.
In contrast, bread made with commercial yeast contains a single strain of yeast and therefore the flavor profile that is developed is nowhere near as complex. To counter this, industrially produced bread contains a slew of additional ingredients to add flavor to the bread, most notably sugar.
Highly processed bread made with modern production methods have a very different texture to bread that has undergone traditional fermentation. Roll up a ball of processed bread and it sticks together into a tight ball and almost returns to its dough form. Sourdough bread on the other hand has a very robust structure. See for example this video demonstrating how a sourdough loaf behaves after having been squashed flat. Try the same thing with a loaf of Wonder Bread and it most certainly will not bounce back and retain its structure in the same manner. This structure is what gives sourdough bread it’s satisfying, chewy texture.
Production of natural preservatives
The lactobacilli bacteria in sourdough produces organic acids and antibiotic compounds that prevent competing microbes (non-sourdough microbes) from colonizing the culture.
This biochemical defense extends the shelf life of bread by acting as a natural preservative.
There is a relationship between a bread’s acidity and its keeping quality. As acidity increases so does the shelf life of the bread. Historically, rural Europeans baked bread only once every two to four weeks. The only breads that could keep that long naturally were bread with high acidity, i.e. sourdough bread.
This is why, though we don’t use preservatives or anti-moulding agents in our products, our sourdough breads last longer than our regular loaf-style breads.