I'm going to assume that "country style ribs" are the ones where you cut them apart first before cooking ... I'd wager a guess that everything is near bone, and a thermometer might have problems with this particular dish. If nothing else, as you can't insert it deeply enough into the thing you're taking a measurement of, there might be enough conduction along the probe for the oven temperature to throw off the reading.
Could you tell us how far the probe was in the meat? I'd assume anything less than about 1/3 the probe might be problematic, with 1/2 or more being better.
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All of that being said, are you sure it's an issue with the placement of the probe, and not a problem with the probe itself?
I've had a number of them go out over the years. I've actually given up on them, and gone back to an instant read thermometer, as I'm up to 4 of the bases (can still use 'em as a timer), and no working probes. (if anyone knows any brands that sell the replacement probes individually, or even better in multi-packs, I'd be willing to go back to using them)
To calibrate -- mix some ice water, and put the probe in there. It should read 32F or 0C. (if it even goes that low, not all do). Boil water, and read the temperature of it, and it should read near 100C or 212F (possibly lower, if you're above sea level). Compare it to another room thermometer after it's been sitting for a bit ... they should read the same.
Don't try to put it into the oven directly ... you could melt the probe ... that's how I lost the first one, so you can't try to compare it to your oven thermometer.
It sounds as if you have meat that has been cooked past the point of well done, so that all of the proteins as as contracted and tough as they are going to be, without the couner-veiling benefit of having collagen conversion.
Your only recourse, which may or may not give you results you find acceptable, is to resort to mechanical tenderization. Your best bet is to grind it in the food processor.
Since you mention making dumplings, a healthy portion of cooked cabbage, mushroom, or other vegetables in the filling will also help get a more appropriate texture.
Best Answer
The only thing that gets the connective tissue in tough cuts to loosen is heat. With the lid on, you've got more insulation. I'd bet you a shiny nickle that the meat towards the bottom of the pot was a touch more cooked than the meat at the top of the pot— you're losing a lot of heat where all of that liquid is hitting room-temperature air. With my immersion circulators, for example, I can't keep the water bath much above 70c without covering them, but the second I cover it, the temperature shoots right up. So sure, the lid likely made it cook a little more quickly and evenly. That said, allowing your cooking liquid to evaporate and intensify as you stew your meat can be a good thing too.