Cooking Time and Temperature

Ingesting the wrong E. Coli bacteria can ruin your picnic. And your kidneys.

As the food we cook is generally meant to be fed to humans, making sure it is safe for consumption is important. Heating food to destroy harmful bacteria is a common way to reduce risk for foodborne illness. Controlling cooking time and temperature allow a cook to maintain acceptable safety while causing minimum damage to food texture and taste.

Background

There are two types of foodborne illness: infection and food poisoning.

Infection occurs when microorganisms directly penetrate the body and grow. Sometimes these organisms can also secrete toxins. Examples include salmonella, trichinella spiralis, E. coli (certain strands), Listeria monocytogenes, and prions like BSE (mad cow). Noninvasive infection primarily involve organisms such as the tapeworm that live inside humans and, while there, secrete toxins that do damage.

Food poisoning is caused by toxins already in the food. This causes the most rapid onset of symptoms (1-6 hours) as toxins are already present and no infection needs to happen. Examples include C. botulinum, Salmonella and Staphyloccus aureus.

The possibility of symptoms from both bacteria and their toxins is why we cannot leave meat sitting in our refrigerator for too long, cook it to a "recommended temperature", and then still eat it. We could kill the active microorganisms but their toxins wouldn't go away. Foodborne illness happens on many different foods, but most people don't cook things like vegetables to make them safe. As a result, this entire guide will focus on the other problem of killing bacteria before they have already contaminated meats.

Time and Temperature

Pasteurization depends on time and temperature. As temperature increases from freezing, bacteria thrive and multiply more rapidly up to a point where they start dying. For example, each 15.2 minutes at 130 degrees Fahrenheit kills 90% of intact Salmonella bacteria. At 140 degrees Fahrenheit, this happens every 2.76 minutes. Each time this 90% killing happens is called a decade reduction. So a 2D reduction is 99%, a 99.99% reduction is 4D, and so on. If that 15.2 minute reduction is 1D, then a 5D reduction would take 15.2x5 or 76 minutes, killing off 99.999% of bacteria.

General FDA recommendations for fresh food are to reach a reduction level of 6.5D, or 99.99997% of pathogens present. When we're cooking on the stovetop or in the oven, there is no way to have this level of control over keeping the food at a particular temperature throughout much less time its holding for pathogen reduction against the guidelines. When we cook sous vide, however, we can estimate the time it takes even the center of the food to reach a temperature, and hold it at a pasteurization temperature to achieve the recommended guidelines.

See Also

• Is it done yet? a food safety guide from the USDA.

References

• Mhyrvold, Nathan et al. Modernist Cuisine: The Art and Science of Cooking. Bellevue, Wash.: Cooking Lab, 2011. ISBN 9780982761007. Vol. I pages 110-112, 192-194.
• Baldwin, Douglas E. Sous Vide For the Home Cook. Incline Village, Nev.: Paradox Press, 2010. ISBN 978-0-9844936-0-9