I often cook chicken thighs in my InstantPot pressure cooker, 12 minutes on high with a marinade and it turns out tender and perfect each time.
This time, however, the thighs were still a little frozen. I had let them thaw for 2 days in the fridge, but I could tell when I squeezed them that they weren't thawed all the way through.
I put them in the InstantPot for the same amount of time with the same settings, and they came out quite tougher than usual (but still done all the way through).
My theory is that it took the Instant Pot longer to get to pressure due to the temperature of the chicken thighs, and so ended up cooking them longer…
What could be the cause of the dramatic difference in toughness?
Best Answer
I'm assuming since you said "this time... still a little frozen" that you were starting from frozen Thighs the times you had success, and that the only real difference is that these particular thighs were not fully thawed. If that's not the case you could have another issue entirely.
In these kinds of situations I think the best we can do is use the information available to try and guess at the cause. Rather than the issue being that the thighs were overcooked and thus tough, I think the issue was likely that the thighs were less cooked than the tender ones you're used to. If you're leaving the Instant Pot for the same amount of time, the internal temperature of the chicken thighs would not effect the overall temperature of the device much at all since it is insulated by the surrounding meat.
Starting from a cooler interior of the chicken thighs (frozen vs refrigerated) could mean that the thawed thighs were cooked past the threshold of toughness and into the point of being soft/tender again, whereas the frozen thighs wouldn't have yet reached that point due to the temperature difference.
This is, however, just a guess. The only thing you could really do if this happens again, to try and test this, would be to put the thighs back in and cook them for a proportionately longer time.
Best of luck!