Killing bacteria is always a matter of temperature and time. So, the exact same level of food safety can be achieved by cooking the meat to a lower temperature and ensuring that it stays at that temperature for a prescribed length of time. The lower the temp, the longer the time necessary to kill off any potential pathogens.
The Food Safety and Inspection Service of the USDA has published complete tables of times and temperatures for safe cooking. So, if we prefer the much juicier texture of a chicken breast that’s cooked no hotter than 150 degrees, a glance at the chart (on page 37 of that PDF) tells us that it’s necessary to hold the chicken at 150 degrees for just under 3 minutes in order to make it safe. (If we were cooking a chicken thigh, which contains more fat, we’d need to hold it for an additional minute, since fatty meat heats through more slowly than leaner meat.)
If we want to cook chicken to just 140 degrees, that’s safe too: this ultra-juicy temp, inside a crisped skin, is not uncommon in restaurant preparations! Safe, says the USDA, as long as it stays at that temp for a full 28 minutes. Sous vide is the easiest way to achieve that sort of long, low-temp preparation.
For beef, the idea is the same, but the numbers are different (see page 35). The standard USDA recommendation of 145 degrees actually assumes that the beef will stay at 145 for 4 minutes. If we want an instantaneously safe temperature, we have to go up to 158, where beef becomes dry and crumbly. A 135-degree steak is food-safe after its center has been at that temperature for 36 minutes—again, that’s optimally achieved with sous vide.
