Kitchen Adventures

Two cereal grain products: The microbiology of sourdough and brewing beer

Bread and beer are as old as recorded history, and likely older. Infact brewing beer arguably pre-dates bread. While the first cereal grain uses were an edible porridge from collected wild grass seeds, the first brewer of beer likely left saturated grains in a container to be rained on then spontaneously fermented by wild yeasts. From then on, mankind’s insatiable appetite for alcohol was ignited. Some historians even argue that the desire for alcohol, not food, is what triggered mankind to first domesticate wild plants and invent the practice of agriculture.

In the beginning…

…both breads and beer were mysteriously transformed into airy and alcohol containing products by an unknown force. Inadvertently, mankind and the microbes responsible for fermentation greatly influenced each others’ futures as they co-evolved. By another chance discovery, the mash paddle, an item used to stir beer in the brewing process, was found to consistently produce beer if it was left uncleaned between batches. Even though the living microbes that caused this magical phenomenon were not yet discovered, humans were unknowling selecting and genetically engineering Saccharomyces cerevisiae for as long as beer has been brewed.

While this artificial selection had been occurring unwittingly, the discovery of fermenting yeasts and subsequent patenting of pasteurization by Louis Pasteur in 1865 in an attempt to fight the souring of wines marked the first time in human history that specific microbes could be targeted for fermentation and conversely, be targeted for destruction by pasteurization.


Natural yeasts have an alcohol tolerance around 5%. Many, many examples in nature of animals getting drunk in nature but not to much of a negative effect may be explained by this limiting factor. In fact ethanol is a potent energy source that humans developed a detoxification mechanism in the liver in order to tap into to gain an evolutionary advantage. Humans both intentionally and unintentionally have selected strains of yeast to tolerate increasingly high alcohol levels. Many varieties of Saccharomyces cerevisiae now exists with very distinct flavor characteristics. With the advent of pasteurization and sanitation techniques, beer is now a sterile and carefully controlled environment to ensure only the desired varieties colonize the wort (unfermented beer).


Initially, the microbe responsible for sourdough was thought to only exists in San Francisco, despite sourdough having existed all around the world for all of recorded history. Thus the bacteria was named Lactobacillus sanfranciscensis  and has amazingly only ever been found in sourdough but not nature despite all sourdough being inoculated by wild microbes.

Anyone just about anywhere in the world can capture wild microbes to start a sourdough culture. Like beer, the yeasts produce ethanol and carbon dioxide. What separates sourdough from normal bread baking is the inclusion of bacteria that produces lactic acid. All that is needed is a yeast that doesn’t care for maltose and a bacteria that thrives on maltose. The latter is what provides the lactic tang to sourdough. Compared to the carefully controlled environment provided by brewers of beer, sourdough is uncontrolled and wild.

My mother is fascinated that my loaves of bread are risen by nothing more than some wild microbes I captured from the barnyard. My recipe only contains flour, water, salt and the wild microbes!


Both processes involve inoculating cereal grains with yeast to produce carbon dioxide and ethanol. Of those byproducts, beer releases the carbon dioxide while retaining the ethanol. The exact opposite is true in bread baking: the alcohol is cooked off while the carbon dioxide is trapped within the elastic gluten yielding the bubbles in the crumb of bread.  Sourdough microbes are relatively uncontrolled when contrasted to carefully selected inoculation of sterile microbe-food in beer wort.

To be fair, spontaneous fermentation is also used in a very small proportion of beer styles referred to as sour beers like belgian lambics. It is certainly an acquired taste and one that I’ve acquired fiercely.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s