Just like any form of life, microbes need energy. To get it, they consume molecules they come into contact with for sustenance. No metabolism is perfect, though, and even the smallest meals produce waste products, a process known as fermentation. A microbe’s trash can be a treasure to us, though—these waste molecules are key ingredients in the fermented foods and drinks that are cornerstones of cuisine around the world.

Fermentation works by feeding sugars to microbes like yeast, a fungus, or a bacteria such as Lactobacillus. The two types of microbes have different means of processing the carbohydrates they dine on. For bacteria, the end product of fermenting sugar is a simple molecule called lactic acid, a weak acid with a rather sour taste. Yeast, one the other hand, produces a molecule called ethanol, the inebriating agent in alcohol. Humans figured out early on that both of these waste products could create tasty dishes while also helping food keep longer, as demonstrated in the three recipes below.


Fermenting vegetable matter with bacteria (specifically strains of Lactobacillus) produces sour-flavored, long-lasting treats. Better known as “pickling,” this process is used in cuisines all around the world to crafts foods from kosher dills to kimchi. The process is thought to have originated thousands of years ago in Egyptian society.



Fermenting grains or fruits with yeast is a tradition at least as old as pickling, and one that’s also known around the world. Luckily for folks who enjoy a beer or glass of wine with dinner, yeast converts sugars into alcohol instead of lactic acid. While the two substances have similar chemical formulas (lactic acid consists of six hydrogen molecules, teamed with three carbon and three oxygen atoms, while alcohol binds six hydrogen atoms to a pair of carbon atoms and a single oxygen atom) they do very different things when they come in contact with our bodies and communicate with our brains—hence the difference between sour-tasting pickles and inebriating beer.

Sourdough Bread


But what happens when a concoction combines Lactobacillus and yeast? Sourdough bread is a good example of this forced symbiosis. Bakers have taken advantage of a wide array of Lactobacillus species and their close relatives to produce three kinds of sourdough bread. The lactic acid from the bacteria and carbon dioxide produced by the fermentation of yeast give this bread its distinctive tangy taste and fluffy texture. The fermentation process also converts the linoleic acid in bread flour into fatty acids that resist the growth of mold and help the loaf stay edible longer, a quality that made this food a favorite among gold surveyors in California. In addition, the presence of yeast means that sourdough freshly out of the oven will have some alcohol in it, although this content evaporates as time goes by.

Discover the importance of microbes in the Musuem’s new exhibition, The Secret World Inside You, now open.


Images: AMNH/M.Fearon