By Eben van Tonder, 29 April 25
Dr Karl Bernhard Lehmann (1858–1940) was a leading German physician, hygienist, and toxicologist whose work significantly contributed to the early scientific understanding of food safety and chemical hygiene. In the late 19th and early 20th centuries, the title “hygienist” referred to a specialist in public health, sanitation, bacteriology, and disease prevention, a role far broader than our modern understanding of personal hygiene. Hygienists like Lehmann were among the first to systematically investigate the hidden forces of chemistry and biology that affected everyday life, from workplace safety to food preservation.
Lehmann’s research into nitrate and nitrite chemistry, conducted alongside contemporaries like Dr Karl Kisskalt, helped establish the foundation for understanding how meat curing really works. His contributions to bacteriology and chemical safety laid critical groundwork for the modern food industry and public health regulations.
The image above is based on an actual historical photograph of Dr Lehmann from the period, capturing his dignified and determined character. He remains one of the great, often unsung, figures in the scientific story behind the foods we still enjoy today.
Introduction
This series is based on my full technical article “Nitrosamines, Cured Meats, and Human Health: A Critical Review of Risk and Physiology”.
The outline we are following is:
1. Understanding Amines and Nitrosamines (done yesterday)
2. Historical Context: The Evolution of Concern About Nitrosamines (today)
3. Mechanism of Nitrosamine Formation: The Chemistry (next)
4. Health Risks: Separating Fact from Fear
5. Mitigation Strategies
6. Regulatory Frameworks
7. Future Directions
I am retelling the story here in a way that makes it accessible to everyone interested in the real science behind cured meats and health.
When we look back at the history of meat curing, it is important to realise that for thousands of years, people cured meat without understanding what was happening on a chemical level. They knew that salt and saltpetre preserved meat and gave it a pleasant pink colour, but they did not know why.
That started to change toward the end of the 19th century. In 1899, a breakthrough came when two German scientists, Dr Kisskalt and Dr Lehmann, conducted experiments that would forever change our understanding of curing. They proved that it was not nitrate itself that preserved meat and gave it its pink colour — it was nitrite. They showed that bacteria naturally present in meat converted nitrate into nitrite, and that nitrite was the true active agent in the curing process.
This was a turning point. Instead of relying on slow, unpredictable bacterial action to create nitrite from nitrate, future scientists and butchers began adding nitrite directly in controlled amounts. It made curing faster, more reliable, and safer.
Celebrating Dr Karl Kisskalt and Dr Karl Bernhard Lehmann: Pioneers of Meat Curing Science
Dr Karl Kisskalt (1867–1933) was a German hygienist who worked in the vibrant scientific environment of Germany at the end of the 19th century. He held positions in public health and medical statistics, fields closely tied at the time to the emerging science of hygiene — a discipline that included bacteriology, sanitation, and food safety. Kisskalt worked primarily in southern Germany, alongside leading figures of the hygiene movement.
He is best remembered for his collaboration with the senior scientist Dr Karl Bernhard Lehmann (1858–1940), a renowned hygienist and toxicologist based in Munich. Together, Kisskalt and Lehmann conducted pivotal experiments that proved for the first time that nitrate (saltpetre) added to meat was biologically reduced to nitrite by bacterial action and that it was this nitrite that caused the characteristic pink colour and curing effect in meats. While Dr Eduard Polenske had earlier speculated about bacterial reduction of nitrate, it was Kisskalt and Lehmann who provided the experimental proof, forever changing the scientific understanding of meat curing.
At the time, “hygienists” were the cutting edge of public health science, investigating not just personal cleanliness but the chemical, bacteriological, and environmental factors that shaped human health — including food preservation.
No known photograph of Dr Karl Kisskalt survives. The image shown here is a modern artistic representation, capturing the spirit of the man and the era in which he worked, when careful observation and scientific curiosity began to unlock the secrets behind one of humanity’s oldest food preservation techniques.
Today we celebrate Dr Karl Kisskalt (1867–1933), a German hygienist whose careful experimental work, in collaboration with the senior scientist Dr Karl Bernhard Lehmann (1858–1940), paved the way for everything that followed in our scientific understanding of meat curing. Together, they provided the first clear experimental proof that nitrate, traditionally used in curing, was biologically reduced by bacteria into nitrite and that it was nitrite, not nitrate itself, that caused the preservation and colour development in cured meats. Their work transformed what had previously been an art guided by tradition into a science based on verifiable chemical principles, setting the stage for all modern curing methods that would follow.
While curing was becoming better understood, the 20th century brought a new challenge nobody expected. Scientists studying the chemistry of cured meats began to notice that under certain conditions — particularly at high cooking temperatures — new compounds were forming. Some of these compounds belonged to a group called nitrosamines.
In the 1950s and 60s, chemical analysis improved dramatically. For the first time, researchers were able to detect trace amounts of nitrosamines in fried bacon. Alarm bells started ringing. Nitrosamines were related to compounds known to cause cancer in laboratory animals. What had been considered a safe and noble tradition, curing meat with saltpetre and later nitrite, now had a shadow hanging over it.
The public reaction was swift and emotional. News stories warned about the dangers of cured meats. Health authorities debated banning nitrite altogether. Some scientists called for urgent action, even though the evidence at the time was incomplete. In many ways, the fear spread faster than the science.
It is important to understand the historical moment. The world had just emerged from the trauma of chemical weapons in the world wars, and there was growing mistrust of anything involving chemicals. Even though nitrite curing had been part of traditional foods for centuries, it was suddenly seen with suspicion.
This was the beginning of a long journey: to investigate the real risks, to find ways to make curing even safer, and to balance tradition with new scientific knowledge. Much of the work we will discuss in the next articles — such as blocking agents like ascorbate and regulations limiting nitrite levels — came directly out of this moment of discovery and fear.
Today we look back and honour the careful scientific work that began with men like Dr Kisskalt. Without their curiosity and commitment to understanding the hidden forces behind food, we would never have built the foundation for the safer, better meat products we enjoy today.
References:
- Van Tonder, E. (2024). Nitrosamines, Cured Meats, and Human Health – A Critical Review of Risk and Physiology. EarthwormExpress.
- Kisskalt and Lehmann (1899), historical work referenced in Van Tonder (2024) EarthwormExpress.
- Pegg, R.B. & Shahidi, F. (2000). Nitrite Curing of Meat: The N-Nitrosamine Problem and Nitrite Alternatives. Food & Nutrition Press.
Tomorrow’s article will explore the actual chemical mechanism:
“How Nitrosamines Form: The Chemistry Behind It.”
We will explain how nitrite and amines react, under what conditions nitrosamines are created, and why cooking methods matter.