The amount of time it takes to cook your tenderloin using the sous vide method depends on the thickness of the thickest part of the loin. Typically a loin will be about 4 inches thick at the thickness part. I like to allow for an hour of cooking per inch, with an hour 'wiggle room'. Traditionally, beef tenderloin is seared in a high heat pan to give it a crust and to set the fibers of the meat followed by a lower temperature cook. By pre-searing the beef in a cast iron pan before placing it in the sous vide bag, you are not only setting the fibers of the beef but caramelizing the meat to bring out its natural flavors giving the tenderloin flavors to self baste in as it cooks. Searing it a second time on the grill or back in the cast iron pan will give the beef tenderloin an amazing crust and a full mouth texture experience.