Blood, chocolate, MacConkey, Miller, and Sabouraud are only some of the types of agar used today. Agar is a polymer of agarose and agaropectin and is found in the cells of red algae of the genera Gelidium and Gracilaria. Nowadays, agar is one of the most important nutrient media in microbiology, and we have a housewife to thank for its discovery.

The beginnings of Fanny Hesse

Fanny Hesse, born Angelina Fanny Eilshemius, was born in 1850 in New York and was raised in New Jersey, the eldest of ten children. She learned to cook and take care of the household from an early age. Aged 15 she was sent to Switzerland, where she studied French and home economics. In 1872, on a trip to Germany, she met Walter Hesse, a microbiologist whom she married shortly after.

Walter Hesse worked at an institute in Berlin, under the mentorship of Robert Koch, where he researched air quality and firmly believed that microorganisms are all around us. He used a series of filters to isolate and study bacteria but soon discovered that he could not grow these microorganisms. Upon consulting with Koch and other scientists, he realized that no one had an ideal solution. Some scientists used potato slices on which, according to some sources, the bacterium Bacillus anthracis was isolated for the first time. This method was crude and ineffective for many bacteria. An alternative method was to use gelatin. This was a much better option, but it had major drawbacks – many bacteria contained enzymes that could break down the proteins in gelatin consequently destroying the substrate, plus gelatin would melt in high summer temperatures.

An addition to pudding or a microbiological discovery?

Fanny, in addition to being a housewife, was also Walter’s assistant in the laboratory, where she cleaned equipment and made illustrations. One summer afternoon, while they were having a break, Fanny brought a pudding for dessert. As they ate, Walter noticed that the pudding was not melting. He asked Fanny how this was possible, to which she replied that she used agar-agar, a substance she learned about from her neighbor who had migrated from Indonesia where agar was commonly used in food.

The discovery of agar was revolutionary. It had high thermal stability, resistance to bacterial enzymes, remained sterile for longer and was suitable for long-term storage. For comparison, agar remains solid at temperatures of up to 90°C, while gelatin melts at 37°C.

Mrs. Hesse’s medium

Thanks to this discovery, Robert Koch was able to grow and identify the causative agent of tuberculosis, Bacillus tuberculosis, which is why some consider him the father of bacteriology. In his paper from 1882, he stated that he used agar as a nutrient medium and listed its advantages, but he never once in the entire paper mentioned or gave credit to Walter and Fanny Hesse.

But Fanny’s contribution did not go unnoticed. In 1939, two medical historians, Arthur Hitchens and Morris Leikind wrote an article about the implementation of agar as a nutrient medium. They contacted surgeon Francis Hesse, Walter and Fanny’s son, who gave them information about the life and work of his parents. Given that her contribution forever marked microbiology Hitchens and Leikind ended their article with the wish that agar would be named Mrs. Hesse’s medium/substrate, thus perpetuating her name. Sadly, this did not happen and her name remained relatively unknown in the world of microbiology.

Translated by: Josipa Radeljak


Literature sources

1. Fanny Hesse, the Mother of Bacterial Cultures, 2002,, pristupljeno 8.11.2022.

2. The Forgotten Woman Who Made Microbiology Possible, 2014,, pristupljeno 8.11.2022.

3. Why is agar used in microbiology?, 2020,, pristupljeno 8.11.2022.

Photography sources

1. Representative structure of agarose and agaropectin,, prisupljeno 8.11.2022.

2. ©[Anna Shvets] via