Day to day, I teach people to make slow fermented sourdough bread at home. There are many reasons to make your own sourdough bread. It’s inexpensive, delicious and if you choose to use local or organic flour, then it is also a wonderfully sustainable way to bake. The question I am asked most, however, is about the digestibility of sourdough, and more specifically, why is it that some people find they can digest some sourdough bread with ease, but not all sourdough?
The first thing I need to stress is that I am not a scientist. I am a baker with a passion for sourdough. But my teaching has caused me to read and research further into the question of digestibility. I’ve discovered that not all sourdough is created equal. Why might some people find genuine sourdough more easily digestible?
No artificial additives
I understand genuine sourdough to be bread made with just flour, salt, water and a wild yeast culture (a mixture of naturally occurring yeasts and lactic acid bacteria). There are none of the processing aids so often found in commercially produced loaves, such as flour treatment agents, emulsifiers, added gluten, preservatives or added enzymes. For some people simply removing this chemical cocktail from their diets and eating traditionally made slow fermented breads may be enough to eliminate digestive problems.
In grain, the principal store of phosphorus is found in the bran part of wheat; this is called phytic acid. Some naturopaths believe that phytic acid causes bloating and flatulence in people suffering from irritable bowel syndrome. During the long, slow fermentation of sourdough, phytic acid is broken down. This may well help with digestibility, especially because, unlike cows who have a compartment in their stomach for fermenting grass, we don’t have a built-in fermentation process in our stomach to break down the acid. Phytic acid also acts to inhibit enzymes that are needed to break down the proteins and starch in our stomachs, and the lack of enzymes results in digestive difficulties.
In sourdough, the lactic acid bacteria produce an enzyme called phytase, which effectively ‘pre-digests’ the phytic acid during the extended fermentation. This partially neutralises the effects of the phytic acid and makes the bread easy for us to digest.
Phytic acid also binds with minerals, such as calcium, magnesium, iron and zinc. This means that our body is unable to absorb and make use of these important nutrients. As the phytase produced during sourdough fermentation breaks down the phytic acid, the minerals remain bioavailable, which is to say our bodies can use them. Simply put, sourdough can be more nutritious because of this. It should be noted, however, that although difficult to square with such evidence, at least one study appears to have found a health benefit to phytic acid, with those on a low phytic acid diet having a greater risk of osteoporosis.
There were some very positive indications in a study published in 2004 that long, slow sourdough fermentation modifies parts of the gliadin protein and the glutenin protein in wheat flour that are toxic to individuals with coeliac disease. Another study that used a mixture of selected sourdough lactobacilli and fungal proteases to eliminate the toxicity of wheat flour during long fermentation reported that “Food processing by selected sourdough lactobacilli and fungal proteases may be considered an efficient approach to eliminate gluten toxicity.”
I must stress that mentioning a laboratory controlled experiment under medical supervision does not give a green light to people suffering from coeliac disease or genuine allergies to wheat or gluten to start eating sourdough bread. It is also important to remember that, increasingly, what is sold as sourdough commercially may not be made with a long fermentation process.
Sourdough may help regulate blood sugar levels
Terry Graham, a professor in human health and nutritional sciences at the University of Guelph in Canada explained to me that his team of researchers studied four kinds of breads to determine which had the most positive health effects when it came to carbohydrate metabolism, blood sugar and insulin levels. The results were remarkable.
The team initially set out to compare the way different types of bread were digested and assimilated into the body. Their results found that the kind of grains used, the way they were milled and the way in which the bread was made, all affect the digestibility properties of a loaf. More importantly for aficionados of sourdough bread, they discovered that fermentation using natural yeasts and lactic acid bacteria resulted in a loaf that was digested more slowly and caused less of a spike in blood sugar levels when it was eaten.
In a second study the team looked at hormonal responses and included other breads in their trials. The results consistently showed sourdough to be associated with more moderate blood sugar responses. So why might sourdough breads show these health benefits? One possibility is that the sourdough fermentation process alters the structure of the bread. These changes mean that the starch could be digested and assimilated into the body more slowly, resulting in less pronounced responses in terms of blood glucose and insulin. Research from Finland has also supported this.
The need to define slow fermented bread
Given that long, slow fermented bread has this potential for human health, especially for diabetics, it seems to me unbelievable that there is no regulation specific to sourdough that stipulates the process of its fermentation. If consumers can’t determine how long a loaf has been fermented, how can they make an informed choice? More importantly how can they identify a bread that can help regulate blood sugar?
Chris Young of The Real Bread Campaign believes that genuine sourdough is made using a dough or batter of water and cereal flour containing a culture of naturally occurring yeasts and lactic acid bacteria. Importantly it is not made using commercial yeast, dried sourdough powder, artificial additives or other acidifiers, such as yoghurt or industrial acetic acid, that merely give a sour flavour without the benefits. There is currently no legal definition of what long, slow fermented bread is in Britain. Does long and slow mean an hour or three or eighteen? The process of making sourdough is an artisanal one because the length of the fermentation process is determined by many factors, including the kind of flour you use, the ambient temperature, the water temperature and the amount of starter used. As a baker I can tell if a sourdough has fermented long enough by the look and touch and feel. Finding an exact definition for long slow fermentation may well be the key to change.
What I do know is that after decades of bland, virtually indistinguishable white sliced factory loaves, there has been a huge resurgence of interest in artisan breads. Britain’s taste buds are being reawakened by a cornucopia of flavours and textures in real bread, crafted by small, local bakeries. In their quest to offer customers a broader choice, their baking has escaped the limitations of typical baker’s yeast and roller-milled, white wheat flour. Customers can now enjoy the added depth and complexity of flavour in the wide array of breads that are now being baked, and perhaps a range of other benefits that only genuine sourdough, slowly leavened with a live culture, can create.
It is maddening that manufacturers are capitalising on the benefits of sourdough and manufacturing cheap, effectively ‘fake’ sourdough bread. For a variety of reasons, increasing numbers of people are prepared to pay a premium for genuine sourdough. That’s why now more than ever, as the Real Bread Campaign has argued, we need an ‘Honest Crust Act’ that includes a legally binding definition for ‘sourdough bread’ and other defining terms including ‘artisan’, ‘fresh’, and ‘traditional’. Some progress has been made in this respect in France, where the pH (acidity) and acetic acid content of sourdough is regulated. Shoppers have a right to know what they are buying and ‘real’ bread bakers, who use these terms legitimately, must be able to distinguish their baking from commercially produced loaves.
In the end the best advice I can offer to anyone is talk to your baker and ask how long the bread is fermented for – or make your own.