There’s something new in the neighborhood. It’s not strange, but businesswise, it’s scary. For the first time ever, bakers must validate that their ovens actually do kill off harmful microbes. Authentication of the kill step in food processing is front-and-center in regulations enforcing the Food Safety Modernization Act (FSMA) — and every food plant must comply.

Get the internal temperature up to 200°F, and nothing lives. That’s something every baker knows, but until now, there was no way to prove it scientifically and in a fashion that a Food and Drug Administration (FDA) inspector will accept. But AIB International, Manhattan, KS, found a means to do so.

“We had to establish the foundational research. There was zero out there,” said Brian Strouts, AIB International’s vice-president, baking and food technical services.

As FDA began discussing how it would write FSMA rules, industry concern soon centered on the need to verify that kill steps like baking dough in a hot oven really did destroy pathogenic microorganisms. Several large wholesale baking companies approached AIB International for advice, starting more than three years ago.

“FSMA rules issued earlier this year clearly stated the need for validating a kill step in the food manufacturing process,” said Lakshmikantha (Kantha) Channaiah, PhD, AIB International’s director of microbiology. Obviously, it’s the oven, but the industry lacked scientific proof of this. “We asked ourselves, what would be considered essential proof? And we decided to get into this matter,” he added.

The American Bakers Association (ABA), through its Food Technical Regulatory Affairs Committee, got involved, too. “AIB International’s kill step protocol is closely attached to ABA’s efforts,” Mr. Strouts noted. 


Led by Dr. Channaiah, the AIB team tapped the expertise of microbiologists at two universities, an emeritus statistician and a Level 2 biolab to pull together the new Kill Step Validation (KSV) protocol. It recruited Kansas State University experts, including microbiologist Randy Phebus, PhD, and Harshavardhan Thippareddi, PhD, from University of Georgia-Athens.

“We needed a top-notch team,” Dr. Channaiah said. “This is the first time that validation of this sort has been attempted.”

Microbiology provided the starting point with basic facts about temperature and microbial death rates. Different microorganisms, even different strains of the same microbe, will vary in the amount of heat it takes to kill them. In general, however, this starts to happen around 120°F and finishes at about 170°F. Buns typically bake in 425°F ovens.

“In the real world, baking usually proceeds to an internal temperature of 200°F, the temperature necessary to set the crumb structure,” Mr. Strouts explained.

Taking this knowledge, the research team inoculated live Salmonella into a bun dough. That’s something no baker ever wants to happen in a working bakery, but this was done in a Level 2 biolab under strictly controlled conditions. “We put in a known quantity of microbes,” Mr. Strouts said. “We were able to determine how much was present before and after baking. This validated what we already knew: The kill stage is well below the gelatinization temperature. The oven effectively kills them all.”

Microbial destruction is measured by x-log reduction in colony-forming units (CFU), in which x represents the decrease in numbers at a logarithmic rate. A 5-log reduction means lowering CFU by 100,000 fold.

“We noticed that FDA has used a 5-log reduction threshold in other industries,” Mr. Strouts said, noting a discussion of this approach with FDA representatives.

That 5-log reduction happens in just half the time required to bake a quality bun, he explained. By the end of the bake, the log reduction is in the thousands. “There’s a lot of safety built into the baking process,” he added. “Now, the industry will have a method that proves this.”

With the reduction rate verified, the team then turned to statistical principles to develop a microbial kinetics-based interactive model — an Excel spreadsheet known as the Baking Process Kill Step Calculator. The baker gathers oven data on time and temperature during the baking process. This information drops into the spreadsheet. The calculator generates the lethality curve, which validates the kill step.

The AIB International team employed live data to develop and test their model. It used data gathered from bakeries around the Midwest making hamburger buns.

Easily applied

Working the calculator is deliberately simple. “All the baker has to do is put in his data,” Dr. Channaiah said. “We had to make the method scientifically valid for the regulators and practical for the baker.”

Mr. Strouts noted, “Bakers are probably already doing what the protocol requires. It is very common for them to use thermal recording devices — data loggers — to look at heat flow within their ovens. It’s information they use to control the bake cycle.”

A data logger simplifies the information gathering. These instruments sit on the oven belt and record temperatures at set time intervals. Their programming not only reports the actual numbers but also provides analytical values for variables described by AIB International’s foundational study.

“Without that data, it’s more complicated,” Mr. Strouts said. “We’re prepared to help a baker go from ground zero.”

The results are a graph of internal temperature vs. time and a process lethality curve that qualifies as documentation of kill step validation, as FSMA regulations require. “Any bakery can use this,” Dr. Channaiah said. “This is the proof, the document, required to validate the process.”

Mr. Strouts added, “What we can’t answer is what the individual inspector will ask for.

“But there is nothing else out there.” he continued. “This will be a published public document for all to read and use. It is based on solid science and strong statistical principles. We didn’t want to publish this just as a research paper; we want it to be publically available.”

The hamburger bun protocol was set to be ready at the end of October, according to Katie Mayes, AIB International’s director of marketing. It will be described in a research paper currently being reviewed by the Journal of Food Protection. Several bakeries are already lined up to test the kill step protocol and calculator.

With hamburger buns now covered, the team plans to take up similar protocols for muffins, cookies and bread. “And we plan to extend this to other products,” Dr. Channaiah said. He noted that bacteria behave differently at varying moisture levels, pH, fat content and so forth.

Stakeholder benefits

Although developed specifically for bakery use, the protocol may have benefits for bakery equipment manufacturers, too, the AIB International team suggested. The group has talked to a number of vendors, particularly oven manufacturers.

“They are interested in demonstrating the uniformity of the oven’s heat profile for baking,” Mr. Strouts said. “Now, that profile can apply to food safety aspects of the oven.

“Any oven will have cool spots, and our model builds in this fact,” he added. “For example, you’ll need to identify the coolest spots in the oven and take temperature readings there, at that cool spot. Such data will also help the oven manufacturer.”

AIB International views the kill step protocol as a stakeholder initiative. “We did the research and developed the protocol so that each individual bakery doesn’t have to,” Ms. Mayes said.

Mr. Strouts added, “This comes out of AIB International’s desire to develop tools that fit within the bakers’ wheelhouse to help them operate better.”