Is there such a thing called overcooked with APC? EXAMPLE: cooking chicken at 154.4°F for 3 hrs. What if I cooked it at same temp but for 5 hrs? Will there be difference? Will the chicken be overcooked???
Thanks
Of course there will be some difference, Snowy.
Why all the question marks?
Chicken legs cooked at your specified temperature for 3 hours wouldn’t likely be considered overcooked, but they’ll be done. 5 hours will get you very done and heading along the road to confit-ville.
What do you consider to be overcooked?
Where i live folks consider chicken falling-off-the-bone and almost cooked dry just right.
I don’t. I like tender and juicy chicken.
Therefore it is up to you to decide. That’s why you should use the precise temperatures and cooking times to cook food exactly the way you like it.
Now with chicken breasts it’s another matter altogether. Chicken breasts cooked at 154.4F for 3 hours will be edible, but a little more solid than i enjoy them. It’s all a matter of personal taste. After 5 hours at 154.4F chicken breasts are going to have that definitely unpleasant mouthfeel of being overcooked, but still moist.
With sous vide cooking, overcooked is a somewhat different thing to the normal understanding of it. Your temperature setting for the water bath determines the end temperature of your food. Time, essentially, gives you the mouth feel and texture that you desire. The collagen that holds the muscle fibres together needs time to convert into gelatin giving that lovely tenderness and mouth feel.
Now, lets have another look at your chicken, and select a boneless breast. If you were to cook it at say, 140F (chicken can safely be cooked at temperatures as low as 130F if taken to pasteurisation but most people find the pink flesh and texture unappealing).
That chicken breast, let’s make it a big one and say it’s 2" thick at the thickest point. In 2 hours the chicken will be hot all the way through, it will have reached temperature equilibrium. At 3.5 hours is will reach pasteurisation point, where any bacteria residing on or in it will be rendered safe. This would be the normal time to pull your chicken out and eat it. The chicken will be beautifully moist and tender but firm enough to slice, and there’ll be no sign of stringiness.
If you leave it longer the collagen will continue to convert to gelatin and the breast will get more and more tender, until it reaches a point many many hours down the track where all of the collagen in the breast has been converted into gelatin and you’re left with a fall apart, mushy blob.
The point is that this happens very slowly with sous vide. If the ideal time for cooking a chicken is 3.5 hours there will be very little noticeable change at 4 hours. You’ll probably notice no real difference at 5 hours, just that it’ll be softer. At 6 hours it will probably still be recognizable and even edible.
I don’t really know where that tipping point is. I’ve not yet been tempted to cook a chicken breast into oblivion to find out. 
But the window for perfection, or near perfection, is very wide.
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Thanks for all the reply!