Case Study 1 — Maya, Her Grandmother, and the Millet Drink She Never Met

In 1987, when Maya Okonkwo's mother boarded a plane in Lagos to begin nursing school in Atlanta, she packed two suitcases and a list. The list was things she would not be able to find in America: dried egusi seeds, palm oil from a particular brand her own mother trusted, three small cassava-leaf bundles wrapped in waxed paper. She did not pack a starter culture for kunu, the slightly fizzy fermented millet drink her family had been making in some form for as long as anyone could remember. She did not consider it. Kunu was made from millet, and millet had to be soaked, and the soaking water had to be left out overnight to do its slow work, and Maya's mother understood — correctly — that the spaces she would be living in for the next decade were not designed for that kind of patience.

She switched to milk.

Maya, born in Atlanta in 1993, grew up on cereal and milk. American milk: cold, high-fat, in cardboard cartons in the school cafeteria. She drank a glass with breakfast every day until middle school. She drank milkshakes after soccer games. She put cream in her coffee.

She also, around age fourteen, started experiencing a phenomenon she did not yet have a word for. It happened maybe an hour after she ate ice cream, or had a particularly creamy bowl of cereal. It was a soft, low-grade discomfort — bloating, a vague rumbling, sometimes more than that. Her mother told her it was nerves, school-related. Her pediatrician told her it might be irritable bowel syndrome and to try a high-fiber diet. Nobody in her early life used the word lactose.

She had a roommate her sophomore year of college from Hong Kong, a chemistry major named Ruoxi, who one day looked at Maya pouring milk on her cereal and said, oh, you can drink that? Maya looked up. Ruoxi explained, mildly, that almost nobody she knew from home could drink milk, and that this was a known thing about adult bodies, and that it had to do with an enzyme. Maya, who was a software engineering student and not yet thinking about food chemistry, googled "lactose" that night. By the end of the week, she had read enough Wikipedia and enough peer-reviewed sources to realize her body had been telling her something for ten years that she did not understand, and that the something was not pathology — it was the default mammalian state. She had simply not known. It is not the kind of thing American pediatric care reliably catches in non-immigrant families, and her mother had quietly assumed Maya would inherit her own mother's milk tolerance, which she had not.

Maya is methodical. She is an engineer by training. Her response to "I have just learned a new fact about my biology" was to design experiments. She bought lactose-free milk and noticed she felt fine. She bought regular milk and noticed she felt bad. She tried hard cheese (extensive aging) and felt fine. She tried fresh ricotta (high lactose) and felt bad. She started reading more carefully about the cuisines of regions where lactase non-persistence is the population norm.

That was the year she started reading about kunu.

The first time Maya made kunu — properly, not as a curiosity — was in the small kitchen of her apartment in the Atlanta neighborhood she shares with her partner Aisha. She had spent two months reading. She had bought a pound of dried millet from an East African grocery in southwest Atlanta. She had read three different recipes from Nigerian food bloggers and one from a food-science journal article in Comprehensive Reviews in Food Science and Food Safety that traced the microbial ecology of West African fermented cereal beverages. She had made charts.

The fundamental procedure for kunu is approximately this. Millet is washed and soaked overnight at room temperature. The soaking water (and, depending on tradition, sometimes a starter from a previous batch) develops a population of lactic acid bacteria and yeasts. The next day the millet is wet-ground with water and sometimes a few additions — ginger, cloves, sweet potato, in different regional traditions. The slurry is strained, sometimes simmered briefly, sometimes not, then sweetened (often with a small amount of sugar) and left to ferment another few hours to overnight. The result is a slightly tart, slightly fizzy, mildly sweet beverage — a non-dairy drink with the kind of fullness and complexity that comes from a microbial culture having had time to do its work.

What Maya understood from her reading, and what she explained to me when I called her about this case study, is that the bacterial culture in kunu and similar beverages is doing several things at once. First, it is converting some of the soluble carbohydrates in the millet to lactic acid, which lowers the pH of the drink to around 3.5–4.0 and gives it its characteristic mild sourness. Second, it is producing trace amounts of carbon dioxide and ethanol — usually well under 1% alcohol, more like a kombucha than a beer — which gives the slight effervescence. Third, the lactic acid bacteria's enzymes break down some of the starch and protein in the millet into shorter, more digestible fragments, including some pre-digestion of carbohydrates that might otherwise cause discomfort.

Fourth, and this is the part that mattered most to Maya, the bacteria's metabolism does not produce lactose. There is no lactose in millet. Millet is a grain. Kunu is, by composition, a non-dairy drink, and an adult body that doesn't produce lactase will go through it without incident.

The first batch she made was thin and slightly off-balance. The second batch was better. By the fifth batch she had developed a feel for the soak time, and her kunu was, as far as she could tell from videos of Nigerian women making it, recognizable as kunu. She called her mother, who tasted it and said: yes, this is what your grandmother made. Where did you learn this?

Maya said: I learned it from a Wikipedia page and a food-science journal.

Her mother laughed. Then, quieter, she said something about how strange it was that the path to her own grandmother's drink had to go through American higher education and an internet article. The drink had skipped a generation; the route back to it had run through chemistry.

The reason this case study lives in the enzyme chapter — and not in the fermentation chapter — is that Maya's experience touches several enzyme stories at once.

First story: lactase. Maya's body stopped producing lactase sometime in early childhood, like most adult mammals. Her cuisine of origin had always known how to feed her. She just hadn't grown up with that cuisine.

Second story: bacterial enzymes. The fermentation that turns soaked millet into kunu is performed by lactic acid bacteria (and some yeasts) deploying their own enzymes — amylases that cut the millet's starch into fermentable sugars, proteases that release amino acids and contribute to flavor, lactic dehydrogenase that produces lactic acid as a metabolic waste. The drink that results is, in a sense, the visible product of millions of microbial enzyme reactions running in parallel.

Third story: pre-digestion. Lactic acid bacteria have, in effect, partly digested the millet for Maya. Compounds that her own digestive enzymes might struggle with (phytic acid in the millet bran; resistant starches; certain bound minerals) have been somewhat broken down by the bacterial metabolism. This is not a unique trick of kunu; it is a general feature of fermented grain drinks across cuisines, from Russian kvass to Korean makgeolli to Mexican atole agrio. The microbe pre-cooks the grain, biochemically.

When I asked Maya whether learning the chemistry had changed how she tasted kunu, she paused for a long time. She said: I don't think it changed how it tastes. I think it changed what I'm doing when I drink it. She said the drink had become, for her, a kind of biological inheritance she had not known was hers — a millennia-old technology her body recognized as friendly, that the American food system her mother had switched her into hadn't included. The chemistry hadn't made the drink magical. The drink had always been chemistry. The chemistry had just made it visible.

There are a few details of Maya's story worth pulling out for analysis.

First, it matters that she was not raised on kunu but had to find her way back to it. This is a common pattern for first- and second-generation immigrant kids whose parents made reasonable choices about what to bring across an ocean and what to leave behind. Some traditional foods come along; some don't. Kunu did not, and Maya rediscovered it in her twenties through a path that went through a roommate's offhand observation, a Wikipedia rabbit hole, and a peer-reviewed paper. Food traditions are sometimes preserved by chemistry as much as by family.

Second, it matters that kunu's benefit to Maya is biochemical, not symbolic. The drink is not just a cultural connection (although it is that). It is an actual non-dairy fermented beverage that her body processes comfortably, that contains B vitamins from the bacterial culture, that delivers slightly sour and slightly fizzy refreshment that hits some of the same comfort notes that dairy hits for other people. The traditional beverage is, viewed through a chemistry lens, a finely-tuned solution to a biological situation. Cuisines optimize themselves to their populations over millennia, even when no one knows the chemistry yet.

Third, it matters that the same logic generalizes. Mongolian airag (fermented mare's milk, the dairy that is not technically dairy because the bacteria ate the lactose). Indian lassi and dahi (fermented milk where bacterial culture reduces lactose). Caucasian kefir. Korean sikhye. Mexican tepache. Russian kvass. The world of fermented grain and milk drinks is enormous, and a substantial fraction of them evolved in populations where lactase non-persistence is the norm. Each one is a biological-and-cultural workaround that predates the chemistry that explains it.

Fourth, it matters that Maya's story is not a story of personal failure or pathology. Her body is doing exactly what an adult mammalian body is supposed to do. Her cuisine had a solution waiting for her. The only reason it was missing was that her family had had to migrate fast, and kunu had not made the trip. Now it has. Her partner Aisha drinks it now too, although Aisha doesn't strictly need to (Aisha is Black-Caribbean and her own family has a different lactose-tolerance distribution, plus she likes dairy, plus the drink is just genuinely good). It tastes nice.

Analyze This

For students or readers who want to engage with this case study analytically:

1. Identify each of the enzyme-related processes happening in a glass of well-fermented kunu. List as many as you can — you should be able to name at least five, between bacterial metabolism, the millet's own enzymes during soaking, and the way the drink interacts with Maya's digestive enzymes.

2. Compare kunu to lassi (fermented milk drink, often consumed in South Asia by populations with widely variable lactase persistence). What chemistry do they share? Where do they differ?

3. Discuss the framing of "lactose intolerance" in light of this case study. Why is the term sometimes considered Eurocentric? What is at stake culturally in choosing between "intolerance" language and "non-persistence" language?

4. Maya describes the chemistry as not changing how the drink tastes but changing "what I'm doing when I drink it." What does she mean? How does food science change a cook's relationship with their own cuisine, even when it doesn't change the recipe?

5. Suggest a kitchen experiment. Design a small experiment in which a reader could compare a homemade kunu-style fermented grain drink against an unfermented millet beverage, holding everything else constant, and detect the differences in flavor, pH, and (if equipment is available) lactose content. What would you measure? What would you predict?

This case study connects to themes #3 (the same reactions appear everywhere), #4 (food traditions are accumulated scientific knowledge), and to the broader argument of the book that the kitchen is a chemistry laboratory whether or not the cook is naming the chemistry.