A guide to choosing quality sourdough bread

1.     WHY SOURDOUGH BREAD?

1.1  WHAT IS SOURDOUGH BREAD?

Sourdough bread is bread leavened by sourdough starter – a culture made up of a community of wild yeast, lactic acid bacteria (LAB), and acetic acid bacteria (AAB). (Bakerpedia.com)

1.2  WHY SOURDOUGH BREAD?

Sourdough bread offers a delightful combination of flavor, texture, and health benefits. It is rich in flavor, gentle on blood sugar, easy to digest, and good for gut health. It also enhances mineral bioavailability while reducing gluten and lectin content in bread. In comparison to other types of bread, sourdough bread is a preferred choice. (Petre, 2023)

1.2.1       IMPROVE THE SENSORY QUALITY OF BREAD

Sourdough stands out with its distinct taste, enticing aroma, delightful texture and visually appealing characteristics (Calvert, et al., 2021).” Its sensory quality is greatly influenced by the fermentation process driven by microorganisms, including both bacteria and yeast.

The bacteria LAB and AAB feast on the flour and spit out CO₂, dextrans, diacetyl, esters, lactic acid, acetic acid, and other organic compounds. Among them, CO₂ causes the dough to rise to give it an airy and light texture; the lactic acid and acetic acid are responsible for the tangy flavor that characterizes sourdough bread; and the other organic compounds such as dextrans, diacetyl, esters, and the enzymes create a bouquet of aroma, taste, gluten network structure, dough elasticity, and various other sensory properties. (Calvert et al., 2021; Holmes, 2020; Landis et al., 2021; Van Kerrebroeck et al., 2018).

Wild yeasts, along with LAB and AAB, also contribute to the sensory qualities of sourdough bread by producing various byproducts such as CO₂, organic acids, and various volatile compounds such as diacetyl, esters, ethanol, and higher alcohols from branched-chain amino acids. Among them, CO2 leads to the rise of the dough and the airy texture of bread; the organic acids, alongside those produced by LAB and AAB, contribute to the slightly acidic flavor of sourdough bread; and the volatile compounds contribute to the aroma of sourdough bread by adding complexity and depth. (Calvert et al., 2021; Vuyst et al., 2016)

What’s amazing about sourdough is that no two starters are the same (Bakerpedia.com). Each starter possesses its own distinct set of microbes which gives rise to a distinct range of aromatic compounds and flavor profiles. For that reason, sourdough bread from different regions and bakeries tends to exhibit a rich spectrum of aromas, tastes, and textures (Landis et al., 2021). This diversity adds an element of adventure to the world of sourdough bread, making every consumption experience truly special and nuanced.

1.2.2       ENHANCE DIGESTIBILITY

Another remarkable benefit of sourdough bread is its enhanced digestibility, thanks to the LAB and AAB in sourdough (Rizzello, 2019).

The LAB and AAB actively interact with the flour, resulting in the production of lactic acid and acetic acid. These acids have a pre-digestion effect in breaking down potential irritants and antinutrients in wheat, thus making the nutrients more accessible and easy to digest (Levie, 2020).

1.2.2.1             ENHANCE MINERAL BIOAVAILABILITY

Take minerals for instance.

Whole grains are rich in minerals such as calcium, copper, phosphorus, potassium, magnesium, iron, zinc, and phosphate. Yet the bioavailability of these minerals is limited due to the presence of phytic acid. As an anti-nutrient that is commonly found in plant-based foods, phytic acid can bind these minerals and prevent them from being absorbed (Petre, 2023).

Sourdough resolves this challenge by releasing organic acids. These acids can lower the dough’s pH which then activates the enzyme phytase (Alder, 2020; Becker, 2005; Holmes, 2020). Once this enzyme is activated, it breaks down phytic acid and turns non-usable minerals into digestible ones. Indeed, in an in vitro study, researchers found that even slight acidification of the dough (pH 5.5) can help to reduce phytic acid by over 70% of the initial flour content (Petre, 2023).

1.2.2.2             REDUCE GLUTEN

Take gluten for another instance.

Wheat contains gluten – the protein that acts as a binding agent to make the dough sticky and give it its structure and shape. Gluten is what makes bread the bread. Without it, bread dough won’t capture CO₂ and rise.

Some people, however, have gluten sensitivity and cannot enjoy bread without experiencing digestive issues.

And sourdough bread solves part of this problem. The bacteria in sourdough can pull apart those disulfide bonds between prolamins – the gliadin storage proteins, and so allow digestive enzymes to break down some gluten proteins into small amino acid fragments or peptides by about 5% (Alder, 2020; Yafa, 2015). Although this is not a complete elimination of gluten content, it does help to ease people’s gluten sensitivity.

1.2.2.3             REDUCE LECTINS

Sourdough also eases the health concern over lectins.

Lectins are carbohydrate-binding proteins – another form of “anti-nutrient” commonly found in all plants, especially in whole wheat grains.

Lectins are necessary in the sense that they are part of the defensive system plants employ to prevent themselves from being consumed. They are, however, indigestible to humans. If consumed raw, they can wreak havoc on health by causing nausea, diarrhea, vomiting, stomach ache, or even autoimmune disease (Harvard T.H. Chan School of Public Health; Wikipedia). 

Cooking can certainly inactivate most of the lectins in food. And sourdough has long existed as another solution in reducing lectins. The fermentation process can break down lectins and make them safe to consume.

1.2.2.4             REDUCE GLYCEMIC INDEX AND IMPROVE GUT HEALTH

Sourdough also helps to reduce the Glycemic Index and improve gut health.

In the realm of commonly consumed food, there exist three types of starch: rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) (Barclay, 2020).

RDS refers to the starch that can be easily broken down and digested in the small intestine. RS refers to the starch that resists digestion in the small intestine, yet ferment in the large intestine. And SDS is somewhere in between. It represents a type of starch that can be digested gradually throughout the entire length of the small intestine (Barclay, 2020).

What’s amazing about sourdough bread is that it can regulate the formation of RS and RDS. Sourdough produces organic acids and these organic acids have a dual effect on starch digestion: increase the formation of RS and decrease the formation of RDS.

An increase in RS provides a valuable source of prebiotics for microbes in the gut and a decrease in RDS limits the rapid release of glucose into the bloodstream. The former helps to boost gut health, while the latter helps to maintain stable blood sugar levels and ease the Glycemic Index (GI) (Barclay, 2020; Demirkesen-Bicak et al., 2021; Liljeberg et al., 1996).

The Glycemic Index (GI) measures how a particular food affects blood sugar levels (Valuepropositions.org on 100% whole wheat bread). While a low GI means food is less likely to spike blood sugar levels, a high GI means the opposite. Regular white flour bread has a GI of 90. Sourdough bread, in contrast, has a GI of 54. That means consuming sourdough bread results in a blood sugar spike that is approximately 54% of the spike caused by ingesting an equivalent amount of glucose over a period of two hours.

What makes sourdough bread even more remarkable is that it can potentially influence the glycemic response of other foods consumed alongside it. Consuming just one slice of sourdough bread has been shown to help reduce the overall GI of foods being consumed in conjunction with sourdough bread (Levie, 2020). That means sourdough bread can contribute to a more balanced blood sugar response to the entire meal, not just the bread itself.

2.     WHAT TO LOOK FOR?

Clearly, sourdough bread has many health benefits. The question is, what to look for when we shop for sourdough bread?

Well, here are a few factors to consider:

2.1  LOOK FOR SOURDOUGH BREAD MADE WITH NATURAL LEAVENING

There are three types of leavening agents for bread: chemicals, baker’s yeast, and sourdough (Rizzello et al., 2019). While chemicals and baker’s yeast are commonly used in commercial baking, sourdough is the natural leavening agent used most often for artisan bread.

Sourdough, also known as natural leavening, real yeast, wild yeast, or sourdough starter, is a living mixture of microorganisms, including natural yeast, LAB, and AAB. These microorganisms are naturally present in the flour and in the surrounding environment such as vessels, bakers, home kitchens, and commercial bakeries (Dunn, 2018).

Given the fact that there exist several hundred species of yeast and several hundred species of acid-producing bacteria in nature (Dunn, 2018), a mature starter can contain a diverse set of yeast species, acid-producing bacteria species, and strains of those species (Calvert et al., 2021).  These bacteria secrete acids and these acids such as lactic acid and acetic acid can lower the starter’s pH to about 3.4 to 4.6 (Modernist Cuisine, 2018). This degree of acidity creates an environment that promotes the growth of acid-tolerant wild yeast while inhibiting the growth of acid-intolerant organisms (Alder, 2020; Calvert et al., 2021; Modernist Cuisine, 2018). To further consolidate their dominance in the starter, LAB also produces antimicrobial compounds such as bacteriocins and antifungal peptides – the natural preservatives – that can inhibit the growth of other microorganisms (Vuyst and Leroy, 2007).

In the meanwhile, the activated wild yeast also produces ethanol to promote the growth of acid-producing bacteria while releasing antimicrobial substances to inhibit the growth of unwanted bacteria (Hatoum, Labrie, and Fliss, 2012; Modernist Cuisine, 2018).

As both the acid-producing bacteria and wild yeast grow in synergy, they evolve into a mature stage upon which the bacterial cells outnumber yeast cells by a ratio of approximately 100 to 1 (Modernist Cuisine, 2018). With this 100 to 1 ratio, the mature starter will then be able to produce the desired shapes, textures, and depth of flavor in bread making.

Commercial baker’s yeast, on the other hand, relies solely on a single species of yeast. It has no bacteria working in tandem to break down anything irritable to the digestive tract (Holmes, 2020). That means there would be no bacteria in place to produce organic acids that can materialize the depth of flavor and the unique characteristics that can only be found in sourdough bread. And that explains why, when only baker’s yeast gets involved in gas production and leavening, the bread will lack flavor and texture profile (Van Kerrebroeck et al., 2018).

So, what to look for when it comes to sourdough bread?

Check for the leavening agent in the ingredient list.

This may not be an easy task for consumers given that the bakers and food manufacturers employ multiple labels to describe sourdough starters. To help consumers to minimize their guesswork, we, therefore, researched 128 sourdough bread products and compiled the following list of labels for consumers’ reference:

In practice, though, some brands would let flour and water ferment naturally over 48 hours without employing any sourdough bread, or some brands would add baker’s yeast on top of sourdough starter to gain some control over the production process. If that’s the case, make sure that the sourdough starter is still listed as the primary ferment, while the baker’s yeast is mentioned as a supplementing ferment.

2.2  LOOK FOR SOURDOUGH BREAD MADE WITH REAL WHEAT

The second factor to consider is the choice of flour

The quality of sourdough bread depends not just on the starter, but also on the choice of flour.

Different types of flour have different concentrations of amylase, lipid profiles, and mix of sugars. These differences can lead to different microbial communities, diverse compositions of lipid-based volatiles, distinct biochemical features, and a range of sensory attributes in sourdough bread (Calvert et al., 2021; Holmes, 2020; Minervini et al. 2012).

For example, using amaranth flour can contribute to the development of starters with a meaty and toasty aroma. Teff and sorghum flours are likely to produce starters with a fermented smell. And emmer and buckwheat flours are known for their potential to yield starters with a vinegary character.

The bottom line is, sourdough is better made with real flour – flour that is unbleached, unbromated, and unfortified (Levie, 2020).

Bleached flour undergoes a process that involves the use of chemical bleaching agents such as chlorine dioxide, benzoyl dioxide, chlorine gas, nitrogen dioxide, calcium and benzoyl peroxides, or Azodicarbonamide. These agents are detrimental to the microbes in sourdough (Bakerpedia.com; Sheehan, 2023); and not surprisingly they are banned in the E.U. and other countries such as Canada and China (Bakerpedia.com on levain; Bakerpedia.com on bleaching).

Bromated flour contains potassium bromate, an oxidizing agent widely used in commercial baking to strengthen the dough and improve its rising capabilities. This agent is classified as “possibly carcinogenic to humans” by the International Agency for Research on Cancer, thus being banned in the E.U., Canada, Brazil, Peru, and China (Weil, 2012).

Fortified flour refers to flour supplemented with added zinc, copper, and iron. The problem with these additives is that they are not plant-based minerals – they are metals and metals are hardly digestible for humans (Hari, 2019).

Of course, ideally, sourdough bread should be made with organic whole grains such as organic whole wheat or organic rye (Yafa, 2015). These types of flours contain not only rich nutrients but also a vibrant array of enzymes and microbes. They can enhance the overall quality of bread and establish a deeper and more pronounced flavor profile.   

2.3  LOOK FOR SOURDOUGH BREAD MADE WITH CLEAN AND SIMPLE INGREDIENTS

The third factor to consider is the clean ingredient.

Sourdough bread is considered one of the least processed and simplest bread options available on the market (Bakerpedia.com on sourdough bread). 

It contains a simple blend of flour, water, and salt while allowing the natural process takes care of the rest.  

Unlike commercial bread, sourdough bread doesn’t require the use of commercial baker’s yeast or dough conditioners. The sourdough starter itself serves as the natural leavening agent.

Besides, sourdough needs no preservatives because the acids produced by the bacteria, along with antimicrobial and antifungal compounds, act as natural preservatives. These compounds eliminate unwanted yeast and bacterial growth, thus preventing bread defects and extending shelf life (Alder, 2020).

Sourdough also eliminates the need for gluten-free substitutes. The fermentation process can help to break down some gluten and reduce its content. For that reason, individuals can safely consume sourdough bread without resorting to gluten-free alternatives, which often contain gluten-free starches, dough conditioners, and excessive added sugar to compensate for their bland taste.

Furthermore, sourdough doesn’t require flavor-enhancing additives such as ascorbic acid, vinegar, or oil. The sourdough starter itself can ferment the flour and generate unique sensory qualities.

By eliminating additives such as dough conditioners, preservatives, gluten-free substitutes, and other unnecessary ingredients, authentic sourdough bread offers a clean and simple product with sophisticated flavors.

Thus, when choosing sourdough bread, it is advisable to look for options that contain simple, recognizable ingredients. Ideally, the bread should consist of flour, water, salt, and a naturally occurring sourdough starter. It is best to avoid bread that contains additives, preservatives, or artificial ingredients.

2.4  LOOK FOR SOURDOUGH BREAD MADE WITH SUFFICIENT FERMENTATION TIME

The last factor to consider: time!

Sourdough bread takes time. It involves a lengthy, multi-stage process that can take several days to complete.

Growing a strong sourdough starter alone takes about 2 to 7 days, and the fermentation of sourdough bread requires an additional 8 to 12 hours (Levie, 2020). In the case of starters with higher populations of acid-producing bacteria, the fermentation process can take an even longer time (Alder, 2020; Petre, 2023).

On the other hand, commercial baker’s yeast is much faster in digesting starch and producing carbon dioxide. It only takes about 30 to 60 minutes to double the size of the dough. And from start to finish, it would take 3 hours with the use of chemical additives and 5 to 6 hours without the use of chemical additives.

The problem, however, is that when speed is prioritized, certain qualities are lost. Quick fermentation does not produce the same depth of flavor found in sourdough bread. It also does not allow sufficient time for organic acids to grow and aid in breaking down phytic acid, reducing rapidly digestible starch (RDS), increasing resistant starch (RS), and transforming gluten into amino acids. Why? Well, for one thing, naturally occurring enzymes, acids, and yeasts require overnight fermentation to break down starches and make them more digestible.

For another, acid-producing bacteria need 2 to 3 days to break down gluten into amino acids (Alder, 2020). Time is essential in allowing wild yeast and bacteria to work synergistically and produce the characteristic digestibility, flavor, texture, and nutritional benefits that would otherwise be lost in a shorter fermentation period.  

It’s thus recommended to look for bread that has undergone a substantial fermentation period, preferably 12 hours or more. This prolonged fermentation allows for the development of desirable qualities in the bread.