Finding the right temperature and time for cooking sous-vide can be confusing, as many sources (both online and in the few books that cover sous-vide cooking) state different ‘optimal’ temperatures. One of the reasons for these differences is personal preference. Although most foodies agree that medium-rare is the best way to serve a steak, there are those who prefer their steak well done (which in my book means ruining it). Sous-vide is a cooking technique for those of you that prefer medium-rare, because if you like everything well done you could simple boil and cook everything to death and be done with it. This reduces your risk of getting sick, but it also reduces the pleasure you get from eating!
Sous-vide gives you perfect control over the temperature regardless of the cooking time, allowing you to serve medium-rare or medium meat that otherwise would not be safe (poultry or hamburgers) or tender (shortribs, pork shoulder, or lamb shank). It is not only the precision of the temperature that makes the difference, but also that with sous-vide cooking, the temperature does not necessarily increase with the cooking time!
Read that last sentence again, because it is very important for understanding what is so different about sous-vide. If for example you cook a leg of lamb, a ham, or a whole chicken in the oven at 180C/350F, the core temperature will increase with time. The longer you leave it in, the hotter the core will become. This is why many recipes tell you to roast something until the core temperature reaches a certain value. At that time, the air around the roast will be 180C/350F, the outer layer of the roast will be close to 100C/212F, and the core will be whatever temperature you were aiming for (for example, 55C/131F), and the rest of the roast will be a ‘gradient’ between 55C/131F and 100C/212F. This means that the core of the meat will be perfectly cooked, but that the outer layers will be overcooked (and thus dry and less tender).
There are two reasons for cooking until the core reaches a certain temperature: to make sure that the meat is pasteurized and safe to eat, and to make it tender. For both of those things to take place, a temperature of 55C/131F (if held for sufficiently long) would be enough. However, if you pull the roast from the oven once the core reaches 55C/131F, the core may not have been at that temperature long enough to be considered safe to eat and/or to become tender. If you leave it in longer, the core temperature will keep increasing, as the oven around the roast is at 180C/350F. And so to get the roast safe to eat and/or tender, you have to overcook it.
With sous-vide cooking, the ‘roast’ will be inside a plastic bag in water that is the same temperature as the desired core tempeture, e.g. 55C/131F. This means that no matter how long you leave the bag in the water, the temperature will never rise above that of the water, e.g. 55C/131F. This means that you can keep it at 55C/131F for as long as it takes to become safe to eat and/or tender, without overcooking!
What does this all have to do with turkey breast? Well, if cooked the traditional way in an oven (or on the grill or on the stovetop), turkey breast is cooked to a core temperature 74C/165F to be considered safe to eat by FDA guidelines. And thus people are used to eating overcooked turkey breast and think it is undercooked and unsafe to eat when it is still slightly pink and juicy rather than white and dry.
With sous-vide cooking however, it is possible to cook turkey breast at 56C/133F that is safe to eat, by keeping the core at that temperature for 35 minutes or longer as that will pasteurize it. Taking into account the time it takes for the core of the turkey breast to reach 56C/133F, the actual cooking time will need to be longer (from 1 hour for a slice of turkey breast that is 2 cm/.8 inch thick, up to 3 hours if it is 5 cm/2 inches thick).
To find out the temperature for cooking turkey breast sous-vide that I like best, I performed a side-by-side experiment.
I started with a nice piece of turkey breast.
I sliced it into 1.25 cm (1/2 inch) slices, and seasoned them with salt and freshly ground black pepper. Then I vacuum sealed them.
I cooked one of those slices sous-vide for an hour at 56C/133F, and another slice for an hour at 64C/147F, as those are two temperature most commonly suggested for turkey breast sous-vide. Both time and temperature combinations are safe to eat for such thin slices (but a longer time would be needed at 56C/133F for a thicker slice).
This is what they looked like after an hour in the sous-vide.
You can see the difference more clearly with the turkey taken out of the bag: the turkey breast cooked sous-vide at 64C/147F has lost considerably more juice than the turkey breast cooked sous-vide at 56C/133F (hardly any visible loss of juices). This is because a higher cooking temperature will make the proteins contract more, and squeeze more juice out of the meat.
When cutting into the meat, you can see that the turkey breast cooked sous-vide at 56C/133F (on the left-hand side) is slightly pink and less contracted than the turkey breast cooked at 64C/147F (on the right-hand side), which is lighter in color and more contracted.
When tasting, I preferred the turkey breast cooked sous-vide at 56C/133F, which can be characterized as ‘medium-rare’. It is more juicy and more tender, and different from what you are used to from eating turkey breast. It is a whole new experience compared to traditional turkey breast, and a better one for my tastes. This is the temperature I prefer.
The turkey breast cooked sous-vide at 64C/147F is still nice, but not as tender and definitely not as juicy. I would characterize is as ‘medium-well’. This is more like traditionally cooked turkey breast, albeit still more tender and juicy and definitely not as overcooked as it sometimes can be. If you or your guests are not adventurous when it comes to food, are afraid of pink-colored poultry and prefer steaks well done, this may be a good option that is still superior to turkey breast prepared traditionally. But it is definitely not my preference.