It may surprise you that sourdough bread is not a trendy product invented by ‘foodies’. It is the way bread has always been made, and if anything, modern yeast bread is ‘trendy’.
The name came from the American gold fields to identify bread made without baker’s yeast… or Bakers. Most don’t realise that until recently, commercial yeast didn’t exist. Various types of leavening agents were used either from ale yeast (barm) or Leaven (or levain or sourdough otherwise levain/sourdough)) - all made by the baker, not purchased. Somebody on the goldfields from the old country knew about this and just did it, to satisfy the demand for the staple food …bread.
It became well known as ‘sourdough’ from San Francisco, because many miners settled there when the gold ran out, and the bread kept being made. But it was still only a miner’s reproduction of what skilled bakers did. As such, it was/is pretty rustic. When I visited in the late 70`s, having just tried Flemish artisan “sourdough”, I was unimpressed by the S.F. sourdough: it was very sour and lacking in technique. But the terminology has stuck.
The art of making good bread without yeast was perfected in many cultures in antiquity. The French claim to be the best and have been the most influential in the baking industry. Hence most modern bakers look to French terminology and methods in an attempt to describe and label their products. Classically, the French call bread made without yeast (ale or otherwise), ‘pain au levain’ ie: bread with leaven. The leaven is understood to be made from flour and water, and this is cultured to capture wild yeasts and bacteria which come from the air and from the flour itself. A symbiotic culture of yeasts and bacteria results, which is then maintained under careful criteria to eventually produce a viable active agent capable of properly leavening bread.
Microbiologically, this culture does not ever contain saccharomyces cerevisiae, which is an ale yeast, now known as bakers yeast. And this is the significant difference between a sourdough and a yeasted bread. Among other criteria, Sourdough is actually defined by the absence of this sacc cerevisiae.
A genuine sourdough is a polyculture of various yeasts and a significant amount of lactobacillus-type bacteria. These yeasts vary depending on the region, and the type of culture maintenance, which depends on the skill of the baker. The leavening of the bread is achieved by both the yeasts and the bacteria, but apart from leavening, a sourdough is a complex fermentation in which the flour matrix is considerably modified, making the minerals and other nutrients in the bread more assimilable and digestible. New nutrients are created in the process also, as proteins are decomplexed, and as the yeasts proliferate, the important protein lysine, deficient in cereals, is increased. The bacteria synthesize some vitamins also, as in yoghurt. Noteworthy is vit B12 (not its analog), which as the S.A. govt analyst noted, is unknown in bread, but is in my sourdough in good quantity.
What I am trying to establish here, is the clear difference between genuine sourdough bread and modern yeast bread, and the difference between a genuine sourdough and a sourdough with added yeast. All of the microbiology I have just mentioned does not happen in regular yeast bread. If the fermentation of yeast bread is extended considerably, even to 8-12 hrs, acidity does develop, which provides some flavour, but that’s all. Nutritionally, its still quite different from sourdough, and all good bakers used to extend this fermentation to ripeness, and those older bakers are disapproving of modern “green” doughs.
In the case of a sourdough/yeast hybrid, there is still a difference in the fermentation, and consequently, flavour and nutrition are still not the same as a genuine sourdough. Sourdoughs often have yeast added, and even the old time bakers did this, but they added a polyculture of ale barm, not the modern (in some cases GMO) baker’s yeast. Some add yeast to reduce sourness, but this can be done with skilled technique.
The yeasts in a sourdough do not digest the carbohydrate maltose, a natural component of a dough. This is done by the bacteria in a sourdough. But baker’s yeast (sacc cerevisiae) does digest maltose. Consequently, when baker’s yeast is added to a sourdough, it competes with the bacteria, and they do not develop as much, which reduces flavour, complexity and nutrition. Some bakers yeasts can’t handle the acidity, and die off quickly, but usually they simply reduce the bacterial component of the fermentation. A result of this can be the formation of more acetic acid in the dough, rather than the organic acids characteristic of sourdough. These organic acids have much to do with flavour, and the flavour of a hybrid is always less complex, with key notes missing and with a compromised crust.
I’m not denying that a sourdough/yeast hybrid can’t be a good bread, they certainly can be. But its not sourdough, and should not be labeled as such. It IS different. Recently I judged the ‘traditional sourdough’ section of a bread competition. Not one got over 50 out of 100, although a few were really excellent long ferment yeast breads, they were not even faintly a genuine sourdough. It is unfortunate that we don’t have regulations covering the name ‘sourdough’, because it allows, quite simply, a deception of the customer. It also prevents any willing baker from making the real thing, because there are no standards to guide them, and many indiscriminate modern texts, including supposedly authoritative ones (Calvel for example) recommend adding yeast. This is making yeast bread, not sourdough.
Americans and Europeans have often commented to me, when they taste my bread, and recognise it as genuine: “Why do Australian bakers put yeast in their sourdoughs?” I`m always at a loss to explain. Is it due to our “she`ll be right” attitude, and we just don’t care? It certainly betrays a lack of skill, because as is well known, a cement worker can make modern bread, and profit highly from it. Why has this skill base disappeared?
Australian bakers once made excellent bread, the equal of any, and sourdoughs were common until WW2. In the UK, our “bloomery” wheats were prized for blending. As the bread industry was lamenting plummeting bread sales in the 1980-90’s, I was gleeful because my sales were soaring…customers vote with their feet. And more customers now know what a good sourdough tastes like, and how good their tummies feel after eating it.
Its time for us to call a spade a spade, and work on our skill levels to provide our customers with a better food. Its not good enough to just call oneself an “artisan”….there’s a meaning there.
The Natural Tucker Bread Book 
by John Downes
Hyland House Melb. 1983.
Artisan Baker Association (ABA)
Email. firstname.lastname@example.org 
Web. www.artisanbaker.com.au