There are a lot of reasons to be careful while doing science at home, especially if you're culturing bacteria: you might just be trying to see how gross your phone with a swab and a petri dish, and unwittingly grow a bunch of staph and strep. Or you might think you've made yogurt from cultures found in your vagina, only for a Dutch microbiologist to conclude that the wooden spoon you used for "collection" is probably responsible for the milk's thick and tangy transformation.
In February, Janet Jay wrote an article for Motherboard about her friend Cecilia Westbrook, who decided to make the "ultimate in locally-sourced cuisine": Westbrook made yogurt at home, using bacteria collected from her own vagina.
Rosanne Hertzberger studies vaginal bacteria at Washington University in St. Louis, and writes a column for NRC Handelsblad, a newspaper in her native Netherlands. She came across Westbrook's experiment and decided to explore vagina-based yogurt cultures herself in a laboratory setting, only to find just how difficult it is to make yogurt from the bacteria found in a healthy vagina.
In her column (paywalled and in Dutch), Hertzberger outlines how internal human bacterial flora is a growing, exciting, and often dirty area of study: The study of gut flora has led to fecal transplants being used to treat intestinal infections. The study of vaginal flora being transmitted from mother to child during birth has led some to treat babies born via Caesarean with the mother's vaginal fluids. Biomedical companies are already trying to figure out how to hack microbiomes to protect against UTIs and, hey, why not, make our genitals taste like diet cola.
"The hypothesis was nice," Hertzberger wrote of Westbrook's experiment, but, "the implementation shabby."
Talking with Science Alert, Hertzberger explains that yogurt is made from a collection of subspecies of Streptococcus thermophilus and Lactobacillus bulgaricus, the latter coming from the same genus as the dominant vaginal bacteria.
When Hertzberger tried to make yogurt in the lab, using Lactobacilli collected from different pregnant women, only one of the eight bacterial strains she tried successfully made the milk it was placed in sour. And even that one was sort of grainy, sour milk, not yogurt.
"The experiment showed that the vaginal Lactobacilli are worthless melkverzuurders," Hertzberger wrote. The Lactobacilli need to work in tandem with a Streptococcus to take milk all the way to yogurt.
She concludes that, in addition to whatever vaginal bacteria was in there, Westbrook's yogurt was probably cultured by something else—likely the wooden spoon Westbrook used for collection, which would be hard to sanitize completely. Whatever bacteria was at work in Westbrook's yogurt could've also come from "the air, or the kitchen sink, or under [Westbrook's] fingernail."
All the same, and with a reminder that you shouldn't try this at home, Hertzberger found that Westbrook's insight was solid, even if the execution could've gotten Westbrook sick. We're going to be seeing more probiotic treatments, likely drawn from our bodies. Yogurt isn't really the end goal or full potential here.
"Westbrook may have gone about her work somewhat clumsily, but her story fits very well in the important trend from anti- to probiotics," Herzberger said. "And as for the unappetizing aspect? I guess we should just get over it."
At a certain point humans got over the unappetizing aspects of collecting milk from a lactating hoofed mammal, getting it all thick and sour, and mass producing it under the name "Go-gurt," so probiotic medicine should probably be a cinch. I mean, bacteria's all over us and our phones already anyway.