The FAQ says that “The device will continue to run at the desired set temperature until you decide you are ready to turn it off. Also remember Sous Vide allows you to leave your food warming without overcooking, so keep that chicken hot if the rest of your meal isn’t ready yet.”
How does it achieve continued cooking (at the preset temp) without overcooking? Can I set it at lower temperature to keep warm, say 145F which is still higher than the FDA food safety recommendation?
The beauty of sous vide is that time is less important than with other cooking methods. This is because the temperature at which you’re cooking (the temperature you’ve set the device) is the temperature you wish your finished product to be. As your product will not go over this temperature it doesn’t overcook.
Think of a piece of steak as an example. You like your steak on the rarer side of medium rare. The ‘doneness’ of a steak is determined by its internal temperature, so to achieve the desired finish you would set your APC to heat the water bath to 53C (127.4F). When the bath reaches temperature you add your bagged steak and let the magic happen. The time that the middle of the steak takes to reach the desired temperature is dependant on the thickness of the steak, so you might choose to leave it for 2 hours.
Again, because the bath is set to the same temperature as you want your steak to be when it is cooked, there is no concern if you don’t get back to the cooker until 3 hours later. There will be no difference in the ‘doneness’ because it can’t go past the temperature of the bath in which it is cooking. Leave it for 4 hours or more and there will still be no change in the internal temperature of the steak.
However, what will happen is that the collagen in the steak will start to break down (as happens with all cooking) and the texture of the steak will change. Given long enough your medium rare steak will go through tender and into the fibres starting to come apart and then beyond that into mushiness.
Now, the food safety aspect comes into things beyond the 4 hours cooking time or for poultry and a few other goodies. The temperatures given in food safety tables as absolutes are actually high enough for instant pasteurisation, that is the product only needs to spend moments at the given internal temperature to be safe. But pasteurisation is a product of both temperature and time. By decreasing the temperature the time must be increased to eliminate harmful pathogens. This is why sous vide is safe at lower temperatures than those normally recommended by food safety agencies.
For a full explanation it is well worth reading the following:
Fully understand. Thanks for the explanation! Cheers!
Another newbie question arises from preparing steak, given that temperature determines directly the degree of doneness, does it mean the level of doneness from 200g of striploin is exactly the same as a 600g , assuming both are cooked in the same bath?
The suggested cooking time and temperature shown in the app specifies the quantity of beef, so I am a bit curious will the cooking time be shortened if the qty is lesser. Thanks
Yes, they can both cook at the same temperature for the same doneness. However, thickness will play a part for time. The thicker meat will need to cook for longer. @Yh_Lee