A Pioneer in Thermal Death-Time Standards

It may be common knowledge today that heat administered over time kills germs, including bacteria in food. But until the early 1900s, it was anyone’s guess for how long and at what temperature food needed to be cooked to make sure it was safe to eat.

That changed in the early 1920s, when several key discoveries were made, among them Charles Olin Ball’s (1893-1970) significant thermal death-time calculations. His formula methods to determine how long it takes to kill specific bacteria at a specific temperature brought such accuracy to food processing that even today his work remains a U.S. Food and Drug Administration (FDA) standard for calculating thermal processes in food preparation.

At around the same time, related research, aimed at producing a calculated lethal effect in bacteria, was performed by Willard D. Bigelow (1866-1939) and James R. Esty (1893-1954), who discovered the relationship of pH in food safety while Ball studied the function of pH in food process calculations. In addition, Dr. Esty and Karl F. Meyer, DVM, PhD (1884-1974), both of the University of California at Berkeley, studied the spores of bacteria and made important discoveries related to safe food processes.

“Ball was a true pioneer in developing organized microbial control in canned foods,” said Irving Pflug, PhD, emeritus professor of food science and nutrition at the University of Minnesota in St. Paul. “In 1920, his original work related to the amount of heat required for canning was certainly a quantum leap in the design and delivery of sterilization processes. In many ways, we haven’t done much to improve things since 1930 or 1935 as far as canning technology is concerned.”

Dr. Pflug described Ball, whom he knew, as a soft-spoken World War I veteran who was fairly conservative but had a lot of ability as a scientist. “When he came out of World War I, someone encouraged him to help solve some of the processes issues,” said Dr. Pflug. “In 1920, when he did all the calculations, all he had was a slide rule. It was before computers and calculators. Someone once said the advance he made in canning in the 1920s [under those conditions] would have won a Nobel Prize today.”

Getting Accurate Numbers

Ball’s discoveries continued earlier work by Nicolas Appert, a French confectioner who in 1810 developed a method for canning (see Food Quality, February/March 2011, “The Father of Food Preservation: Nicolas Appert invented techniques for long-term food storage”). But Appert’s work was in the early days of food preservation, when the details for canning still had to be worked out.

“Appert’s canning method was more of an art,” said Dr. Pflug. “People continued to experiment on how long to cook the food. And they became convinced they needed a more accurate way to handle processes and microbiology.”

A major advance came in 1895, when the William Underwood Company of Boston, America’s first canning company, noticed losses related to swollen and burst cans and asked the Massachusetts Institute of Technology (MIT) for assistance. Working on the problem, Samuel Cate Prescott, a chemist at MIT, focused on canned clams and discovered that they contained heat-resistant bacterial spores that had survived the canning process but that could be killed if they were processed at 250ºF for 10 minutes. The research, which was not patented, paved the way for Ball’s thermal death-time work; Bigelow’s work focused on Clostridium botulinum.

Until Ball came up with his formulae, scientists used graph paper to show thermal death time, reading numbers of temperature versus the time, typically in minutes, to kill organisms off of a paper chart, said Aaron Brody, PhD, president and CEO of Packaging/Brody Inc., a Duluth, Ga., consultancy. “Dr. Ball converted the chart into mathematical formulae. So it was possible to plug numbers into the formulae instead of reading them off a graph. He made it more accurate,” Dr. Brody said. Ball’s formulae turned Appert’s art of canning into a science.