#8 High Heating, Low Heating
Professor Emeritus at Hokkaido University
Advisor at Japan Food Research Laboratories
As I mentioned in my column #2, there are various methods for food microbiological control. Among them, heating is widely used around the world as an effective way.
1. Napoleon's bounty
In 18th century, French Army was carrying on wars all around Europe under the command of Napoleon Bonaparte (1769-1821, Figure1). The army had a lot of trouble in getting food. Napoleon found it important to supply safe, delicious, and nutritious food in necessary quantity even in battlefields in order to maintain the morale and combat power of the army. He encouraged technology development for preserving and distributing food by posting a large amount of prize money.
Nicolas Appert (1749-1841) created a technique to keep food in an airtight container and heat it over high temperature. He won the Napoleon’s prize with this invention. The container was made of glass bottle and cork stopper sealed with wax. Then the container was boiled and sterilized to make the inside food preservable. It was back in 1804.
Six years later, 1810, Britain’s Peter Durand (1766-1822) received a patent for using tin-plate can instead of glass bottle. This gave birth to more useful canned food.
Even though tin-can food was invented, can opener did not exist yet. How did people eat the food inside? Among different stories, most credible one is that people used hammers and chisels. Another dynamic possibility is they used axes for chopping firewood
Without Napoleon’s bounty, heated or unheated canned food might not exist in this world.
The invention of tin can advanced the food processing field and won great popularity of people. What is interesting is that filled and sealed tin cans without heat-sterilization were also created and still used habitually today. This type of cans have been widely used for confectionary such as cookies. Here, I’d like to introduce a terrific unheated canned food produced over the years in Sweden. It’s a can of salted herring called surstrommings. This smells stronger than “kusaya”, horse mackerel dipped in salt water and dried in the sun which is notorious for terrible smell in Japan. Figure1 is an emptied can of surstrommings. Students of the Hokkaido University purchased it via the internet to listen to my lecture, and daringly tried it.
Airline companies do not accept surstrommings on their flights. I suppose this is because people on board cannot escape anywhere if its offensive smell leaks out of can. Canned surstrommings can be shipped by surface mail. Since it’s not heated, the fermentation process continues even after being canned. Therefore, the inside gas pressure gets higher due to hydrogen sulfide, carbon dioxide, etc. and some cans will become deformed and physically dangerous. In case a heated can deforms, something must be wrong with it.
Thus a pressure sterilizing system was developed in Britain and enabled heating of food-filled and sealed tin cans over 100°C. This realized countermeasures against heat-resistant spores such as Clostridium botulinum. Turning 19th century, the United States and other countries started mass production of canned foods. Among them, Japan has been producing large amount of heated canned foods up until today.
2. A temple’s diary and pasteurization
In 18th and 19th centuries, as I mentioned above, people were trying to preserve foods by strongly heating them. Even developed countries of the time had not figured out why foods fermented or decayed. The existence of microorganisms had not been revealed, and people believed there were “good air” and “bad air”.
Louis Pasteur (1822-1895) was born in France and engaged in the research of tartaric acid crystals as a chemist. Then he got interested in the stories of people bothered by decay of wine and undertook researches on microbiology. Now he is called “the founder of modern bacteriology” together with Robert Koch whom I covered in my column #7.
In 1861, Pasteur experimented on heated gravy using a well-known “Swan Neck Flask” with a narrow neck and denied the conventional abiogenesis. In 1862, he began developing a method for decay prevention by heating and succeeded in the invention of low temperature microbiocide on which he wrote a scientific paper. In this method, liquid body such as wine and milk are heated at low temperature around 60°C for tens of minutes to kill microorganisms like food spoilage bacteria. This method is called “pasteurization” (Figure2) and still used all over the world.
In Japan, sake (Japanese rice wine) has been sterilized by heat (“hi-ire” in Japanese) since old times. A temple in Nara named Tamon-in has been handed down a diary which describes “boil sake and put it in a barrel” as of the year 1568. Sake was heated to prevent decay and rancidification (“hi-ochi”). At least 300 years before Pasteur’s invention, low temperature microbiocide called hi-ire was conducted in Japan. Early Japanese people used to pass on skills through non-verbal communication without a custom to write them down in papers. Western people, on the other hand, were accustomed to record skills and techniques in scientific papers and this is why low temperature microbiocide is internationally acknowledged as Pasteur’s achievement. If Japanese ancestors had recorded hi-ire in a paper, the term “pasteurization” would have not existed.
References (all in Japanese)
Japan Canners Association. “200-year History of Canned Foods.”
Shimizu, U. (2012). Shokuhin Biseibutsu no Kagaku (Science of Food Microorganism) --- Shokuhin Biseibutsu Kiso Hen (Basic of Food Microorganism). Saiwai Shobo.