Why does cook time in Sous Vide Toolbox differ from other references?

Using this Time and Temperature Reference Guide the Time to Core Temperature of 130°F for 1 inch salmon filets is 15 minutes. Using the Toolbox the Time to Core Temperature of 130°F for 1 inch salmon filets is 1 hour 39 minutes. Increasing the Toolbox water temperature by 1° C only reduces the cooking time to 57 minutes. Can you help me to understand why there is such a large variance?

The difference is created by the chef’s decision. The app performs a thermodynamic simulation, which is precise to the point. A chef can decide that a shorter cooking time works perfectly well from the perspective of taste, texture and temperature. When looking at the temperature curve in the app, you’ll recognize that a large portion of the cook time is used to reach the final 1-2 degrees of the core. When a chef decides to cook this piece of salmon for 15 minutes, a quick look at the temperature curve will tell that after approximately 15 minutes, the surface has reached 130°F. The core is very close to 130°F at about 50 minutes. So in the case of 15 minutes cook time, the chef is actually accepting that the center of the salmon is two, three, or even five degrees lower than the cooking temperature. The larger this gap is the more clear can one detect it in form of a gradient.

What did PolyScience use to determine the appropriate time and temp to get the desired log reduction?

Here are some of the most relevant sources we used in creating the app. Note that we don’t use their numbers directly, but rather we use the mathematical techniques they describe and model them dynamically for each unique cooking scenario a user enters.

• A. H. Geeraerd, C. H. Herremans, and J. F. Van Impe. Structural model requirements to describe microbial inactivation during a mild heat treatment. International Journal of Food Microbiology, 59:185–209, 2000.

• Lihan Huang. Computer simulation of heat transfer during in-package pasteurization of beef frankfurters by hot water immersion. Journal of Food Engineering, 80:839–849, 2007.

• FSIS. Time-temperature tables for cooking ready-to-eat poultry products. Notice 16-05, Food Safety and Inspection Service, 2005.

Much of the early work in the field was for fixed temperature pasteurization, but but the D_ref and T_ref approach we use is more and more common these days.

The mathematical technique we used is also presented very concisely at the end of Appendix A of Douglas Baldwin’s seminal work at http://www.douglasbaldwin.com/sous-vide.html.