The "immortal" yogurt has been keeping one family – and their friends – in yogurt for more than 4 decades.
Humans have been intrigued by immortality probably ever since we started dying, but as hard as we try, the secret to eternal life eludes us. Not so for a few lucky creatures on this planet. Immortality, of sorts, has graced the immortal jellyfish and the wee little hydra that can live forever; and the even wee-er organisms that constitute the bacteria domain. Although calling bacteria immortal is a bit slippery – they can die – but as they reproduce by splitting, they essentially clone themselves over and over, giving us "biological immortality," the closest thing to eternal existance that we know.
And as it turns out, yogurt can be immortal too, in a way. As Eliza Barclay points out on NPR, in the process that turns milk into yogurt, bacteria grow and feed on the sugar in milk and can procreate indefinitely in new generations of yogurt. This is why you can use an “heirloom” yogurt starter over and over to make an enduring parade of yogurt, all started with, and comprised of, the same bacteria. Many heirloom starters come from places like Finland and Bulgaria which have a long tradition of yogurt-making; these starters are different from store-bought yogurts that only have a few strains of bacteria isolated by scientists and will only go forth for a generation or two.
In the United States most of our experience with yogurt is the sweetened and flavored versions lining the supermarket shelves, although we’re slowly developing a more adventurous streak with other styles making a play for some of the market. But in other places, like India and Scandinavia, yogurt is made at home daily and it tastes distinctly different from our commercial ones; it’s thicker and has more tang.
Which is what led Veena Mehra, who emigrated to the U.S. from India in 1970, to start making her own here. American store-bought yogurt was just not her cup of tea.
"It just did not taste the same," she tells NPR. "I tried buttermilk, and then I tried to use the yogurt I found at the store [as a starter] to make my own, but it just didn't work."
Homesick for homemade yogurt, she decided to bring some yogurt starter back with her during a visit to Mumbai in 1975. She put it in a container and then in her purse; it survived the 21-hour journey back to Tennessee, and in two days she was making tart, thick yogurt like that from her homeland.
Fast forward 40 years, and Mehra is using yogurt from each round as a starter for the next; all originating from the initial batch she brought back from Mumbai. She has been sharing it with other families, and brings it with her when she moves.
Biologically, Mehra’s yogurt is likely very close to its former self circa 1975. Some evolution may have occurred, but since most of the microbes in milk are killed by heat prior to making yogurt, the only active microbes in Mehra’s starter would be the same ones that immigrated by purse to America four decades ago. With a little TLC, they could easily last another 40 years … or 400.