It’s me – I am eating bacteria. And it is lovely.
Consider a simple and reasonably healthy breakfast of buttermilk pancakes and yogurt (all homemade). Or perhaps an afternoon nibble on bread and cheese with a glass of wine. All of these common foods were prepared using bacteria and fungi which, when allowed to grow under the right conditions, transform unpalatable flour into bread, quickly-spoiled milk into long-lasting yogurt, butter, and cheese, and humble grapes into complex wines.
Fermentation of milk into yogurt is a simple and direct example of bacterial intervention in our food. To put it in slightly more scientific terms, we first prepare the substrate (heat the milk to break-up the proteins), inoculate (add bacteria), and incubate (let the bacteria grow).
The heating is done to denature the whey protein lactoglobulin, allowing it to bond to other milk molecules and form a matrix instead of curds. The active bacterial species are Lactobacillus bulgaricus and Streptococcus thermophilus, who work symbiotically to thicken the milk and protect it from spoilage by other micro-organisms. The bacteria acidify the milk as they grow. First S. thermophilus grows more rapidly, but is overtaken by L. bulgaricus as acid content passes 0.5%, creating the tartness of unsweetened yogurt. The finely stranded networks they and the milk proteins create thicken the final product by holding liquid whey in suspension. A higher protein to liquid ratio produces thicker yogurt.
Because low fat milk has fewer milk constituents (fat, minerals and sugars) to bind to the protein lattice, the resulting yogurt can be runny. Yogurt can be thickened by using whole milk, increasing the incubation period, or through the addition of stabilizers such as powdered milk, gelatin or agar. Yogurt can be further thickened to create Greek yogurt – which is simply regular yogurt strained to remove most of the liquid content (the whey). As a result, Greek yogurt has a higher fat and protein content.
It’s simple and cheap to make yogurt at home, just have a look at the full directions in our Lab Book. Given the wide variety of micro-organisms found in our staple foods, one might think that people wouldn’t give it a second thought, let alone shudder in fear.
However, when we think of food borne bacteria we immediately think of E. coli, Salmonella, or the toxic C. botulinum and instinctively reach for the soaps and sanitizers. It’s almost understandable when it’s revealed that even our friendly S. thermophilus is cousins with S.pharyngitis (strep throat), S. pneumoniae (bacterial pneumonia), and Streptococcus pyogenes (flesh-eating disease), the other side of the intentionally ambiguous title to this post.
It was through investigating wine and beer production that Louis Pasteur proved experimentally the role of micro-organisms in fermentation and, by extension, the germ theory of disease. Dr. Joseph Lister applied his work to surgical methods and introduced antiseptic methods to hospitals. Dr. Robert Koch isolated the bacteria responsible for anthrax, tuberculosis, and cholera, and developed Koch’s Postulates, further explaining our interactions with the invisible world.
Remember, Pasteur, Koch, and Lister only made their discoveries within the past 150 years, but the foods listed above have been produced and enjoyed by humans for millennia. It’s too easy for modern people to simplify our relationship with micro-organisms as healthy or unhealthy, good or evil, or even us and them. The reality is that bacteria are a part of us, and we depend on each other.
Some of us depend on the edible (and drinkable) outcomes of bacteria more than others…
You may have noticed a new page at the top of the screen – it’s our Lab Book! We are filling it with directions and recipes relating to our little stories and experiments. Be sure to check it out!