A Kitchen Accident that Rewrote Microbiology
Corrado Nai, writing for Asimov Press, traces the history of agar from a 17th-century Japanese kitchen mishap to its current status as one of the most quietly indispensable substances in modern science. The article, which will appear in the forthcoming book "Making the Modern Laboratory," covers roughly 350 years of agar's journey through cuisine, colonialism, wartime mobilization, and the daily work of microbiology labs worldwide.
The scope is ambitious. Nai moves from the legend of a Japanese innkeeper who accidentally freeze-dried leftover tokoroten soup to the 2024 crisis in which researchers discovered toxic batches of agar disrupting experiments across multiple labs. Along the way, he makes a compelling case that this seaweed-derived jelly is not just useful but irreplaceable.
The Woman Koch Forgot
The article's strongest section recovers the contribution of Fanny Angelina Hesse, the woman who introduced agar to Robert Koch's laboratory in 1881. Nai is blunt about how scientific history has treated her. She is, he writes, often unflattering referred to as merely a housewife or technician.
Her foundational contribution to the nascent field of microbiology is often omitted from textbooks. In other cases, she is unflatteringly referred to as a "German housewife" or as "Frau Hesse," or dismissed as an unnamed technician.
Hesse grew up in Kearny, New Jersey, where her Dutch family learned about agar from a neighbor familiar with Indonesian cooking. She married bacteriologist Walther Hesse and supported his research while raising three children, creating detailed scientific illustrations of bacterial and fungal colonies. When her husband struggled with gelatine media during the hot summer of 1881, she suggested agar based on her cooking experience.
Koch never credited the Hesses. Nai notes that Koch mentioned agar for the first time in his landmark 1882 paper on the tuberculosis bacillus, but the acknowledgment stopped there. Even more damning, Koch continued using gelatine for years afterward, failing during his 1883-84 cholera expedition in Egypt's heat despite having the solution in hand. He only succeeded in colder Calcutta.
Koch never credited the Hesses for their discovery of bacteriological agar, perhaps because, at the time, he failed to recognize its importance.
It is a familiar pattern in the history of science: the person closest to the practical problem sees the solution first, and the person with institutional authority gets the credit.
A War Material Alongside Copper and Rubber
The wartime section is where Nai's research shines most vividly. In 1942, an unlikely coalition of lighthouse keepers, Scouts, schoolteachers, and Royal Air Force members scoured Britain's coastline for seaweed. The United States War Production Board classified agar alongside copper, nickel, and rubber as a critical war material, restricting its civilian use in jellies, desserts, and laxatives.
The most important service that agar renders to mankind, in war or in peace, is as a bacteriological culture medium.
That quote comes from oceanographer C.K. Tseng's wonderfully titled 1944 essay, "A Seaweed Goes to War." The stakes were not abstract. Without agar, countries could not produce vaccines or penicillin. Lieutenant-General Ernest Bradfield warned of a potential breakdown of public health services with "far-reaching and serious results."
The geopolitics were equally tangled. Japan controlled the richest natural agar sources. Nazi Germany relied on submarine shipments through the Indian Ocean from its ally. Japan had halted exports to other nations, fearing agar would support the development of biological weapons. Meanwhile, British volunteers were damming streams to wash seaweed and using hot air from bakeries to dry it.
Why Nothing Else Works
The second half of the article methodically dismantles every proposed agar alternative. Nai walks through carrageenan, bacterial cellulose, guar gum, xanthan, alginate, and gellan gum, each failing on at least one critical dimension. The litany reads like a dating profile of substances that are almost good enough but never quite right.
Agar's advantage is cumulative rather than singular. It dissolves in boiling water for easy sterilization. It sets firmly without refrigeration. It resists digestion by nearly all microbes. It stays transparent for observation. It has low syneresis, meaning plates do not sweat and colonies stay put. It allows chemical diffusion for antibiotic testing.
These new methods proved so helpful...that one could regard them as the keys for the further investigation of microorganisms...Discoveries fell into our laps like ripe fruits.
Koch said that in 1909, though it took him nearly three decades to fully appreciate what the Hesses had handed him.
There is a reasonable counterpoint that Nai does not fully explore. The very dominance of agar creates a kind of methodological lock-in. He acknowledges that scientists are reluctant to abandon established protocols and that switching media would make results incomparable with decades of published literature. But this conservatism cuts both ways. It may be protecting reliability, or it may be blinding researchers to genuinely superior approaches that require a larger upfront investment to validate.
The Gelidium Problem
The article's most forward-looking concern is the fragility of the agar supply chain. Lab-grade agar depends on Gelidium seaweed, which cannot be farmed. It grows slowly in cold, turbulent waters over rocky seabeds, conditions that defy aquaculture. Morocco has been the primary source for at least two decades, and when the country reduced exports in 2015, wholesale prices tripled.
To speak of agar as a single substance of certain (if known) chemical structure is probably a mistake.
That observation from phycologist Harold Humm in 1947 hints at why replacement is so difficult. Agar is not one thing but a variable mixture of complex, poorly characterized polysaccharides. Reproducing its properties synthetically would require understanding a chemistry that scientists still have not fully mapped.
Global consumption of bacteriological agar has grown from 250 tons in 1993 to an estimated 1,200-1,800 tons per year today. Demand continues to rise while supply depends on wild-harvested seaweed from a single dominant source country. The 2024 toxic batch incident adds another layer of vulnerability that Nai wisely highlights without overstating.
The Great Plate Count Anomaly
One of the article's most fascinating detours concerns a phenomenon that baffled early 20th-century researchers: the number of cells visible under a microscope did not match the colonies growing on agar plates. The culprit turned out to be agar itself. When nutrient broths are heated with agar during boiling, harmful byproducts form from the reaction of agar with phosphate minerals in the media.
This points to a broader challenge that Nai frames as microbial "unculturability," the difficulty of recreating on a plate the complex, multi-variable environments in which microbes grow naturally. Agar is the best available tool, but it remains an approximation. The gap between what grows in the wild and what grows in the lab is a standing reminder that laboratory science always involves a degree of simplification that may distort results.
Bottom Line
Nai has written an exemplary piece of science history that gives agar its due as a material every bit as consequential as the discoveries it enabled. The recovery of Fanny Angelina Hesse's story is long overdue, and the wartime narrative is gripping. The article's central insight is that the most important technologies are often the least glamorous. Koch won the Nobel Prize. Hesse got a footnote. The jelly that made it all possible got even less.
Today, the most important product obtained from seaweeds is agar, a widely-used commodity but one that is not well known to the general public.
Humm wrote that in 1947. Nearly eighty years later, the obscurity persists, but this article goes a long way toward correcting it.