A very cultured food

For the first couple of decades of my life, I didn’t know what yogurt was, nor could I understand why anyone would eat it.

For a large swath of the world, this probably would have marked me as a barbarian, because yogurt has been eaten and enjoyed for a very, very, very long time. In fact, there’s evidence that it—and other foods created by the bacterial fermentation of milk—were being consumed almost 5,000 years ago.

Yogurt probably just happened rather being formally invented. Nomadic shepherds often preserved milk in containers made from animal skins or stomachs. At some point, someone found milk that had been forgotten for a while had been transformed into something that was denser and tastier. Eventually, someone else figured out how to make that transformation happen reliably.

UPDATE 05/31/06: A correspondent from Turkey has pointed out that leaving out any mention of the Turks in a column on yogurt was downright negligent. So I’ve added the following paragraph:

Those someones may well have lived in what eventually became Turkey; yogurt is an essential part of Turkish cuisine, and Turks like to claim yogurt as their invention. Certainly the word is Turkish; in fact, the oldest known lexicon of the Turkish language has an entry for the same word, with the same meaning.

Yogurt spread across India, Central and Western Asia and Southeastern and Central Europe. The very first Arab recipe books describe its use, and it features in the banquets described in the famous tales of the Arabian Nights. It was also used medicinally by many cultures, as everything from an aid to sleep to a cure for intestinal problems to a preventative for tuberculosis.

However, yogurt didn’t really make inroads into the West until the 1900s. A Russian biologist, Ilya Ilyich Mecnikov, thought eating lots of yogurt accounted for the longevity of Bulgarian peasants, and so he worked to popularize it across Europe.

A Spaniard named Isaac Carasson figured out how to industrialize yogurt production, starting the first commercial plant in 1919 in Barcelona. He named the business Danone after his son. Today Danone is the biggest yogurt producer in the world. It has about a 30 percent share of the Canadian market—a market that’s growing: Canadian yogurt production grew by almost a third just from 2001 through 2004, and Canadian per capita consumption of yogurt, just 1.61 litres back in 1980, was a whopping 6.75 litres in 2004.

Two main groups of bacteria are responsible for turning milk into yogurt: Lactobacillus bulgarius and Streptococcus thermophilus. These bacteria digest the sugars naturally present in milk and release lactic acid as waste. This increases the acidity of the milk, which causes its protein molecules to tangle up into a solid mass. The increased acidity has another important affect: it keeps disease-causing bacteria from proliferating.

Although they can grow independently, working together the two bacteria produce acid faster than they do when growing on their own. The lactic acid, plus acetaldehyde, acetic acid and diacetyl, other waste products of the bacteria, all contribute to yogurt’s unique flavor. Bacteria, in other words, are an integral part of what makes yogurt yogurt: Canadian standards dictate that yogurt must contain at least 107 CFU/g. (CFU stands for “colony forming unit,” by the way. I looked it up.)

Now scientists have discovered something very interesting about those bacteria. A team of French scientists have published the genome of Lactobacillus bulgaricus, and recently presented their research.

They found that Lactobacillus bulgaricus contains a number of genes for breaking down plant sugars, which indicates the bacteria probably originally lived on plants. Most of those genes are no longer—in fact, the microbe has 270 broken genes, or “pseudogenes,” which is rather a lot, considering it has only 1,562 working genes in total. Other genes appear to have been lost altogether.

How did it lose those genes? Milk contains the sugar lactose, but none of the other sugars the microbe would have feasted on when it lived on plants. Therefore mutations that cost the bacterium the ability to digest those sugars, which would have been detrimental or fatal when it lived on plants, had no affect on its ability to survive in milk. Over time those mutations have piled up.

The bacterium has apparently also lost the ability to make certain amino acids (the building blocks of proteins): instead, it breaks down milk proteins into amino acids and absorbs the ones it needs.

But the bacterium has also gained some genes over the millennia: large portion of its genome, the researchers say, apparently came from a completely different species of bacteria, although they’re not sure yet what those genes do.

It’s something to keep in mind when next you eat yogurt: you’re not just eating a tasty treat—you’re eating evolution in action.

Oh, yeah, and a whole bunch of bacteria.

Enjoy!