As BluDawg says - "You can not cook your pork butt/pork shoulder to a specific temperature and call it done!!!!"
There are a couple of ways to know when pork is done:
The first being the poke test; When you stick it with a thermometer, skewer, fork or whatever, and it goes in without little to no resistance, almost like warm knife goes into cold butter, then it is done.
The second being the bone pull test; When you pull on the bone and it wiggles / slightly twists a little bit, like a loose tooth, then it is done.
The third being the tug test; When you have a boneless pork butt, grab a piece of meat with your thumb and index finger and you are able to pull a piece of meat off with minor resistance, it is done.
Pork butt / shoulder is a very forgiving cut of meat due of the fat content and the amount of connective tissue it contains. If your pork is tough to pull then it wasn't completely done. If the pork simply falls apart when pulling, it is slightly overdone. Even when slightly under-cooked or slightly over-cooked the pulled pork will still be great, however it will never match the taste and texture of perfectly done pork as indicated above.
Every piece of meat is different, and therefore each will cook differently in some manner. I have had many pork butts done as low as 185 degrees, while others do not indicate being done until they reach 200 degrees or more. So temperature is simply a guide to test, not an indicator of being done.
Because of this variance in temperatures, I usually start checking for being done when my internal probe says 180 degrees, after that I don't pay any attention to what the internal temperature is, except for personal reference. The bone is a much better predictor of being done than temperature of the meat, simply put When the bone wiggles like a loose tooth it's done.
The rest after the cook is also an integral part of the final stages of the cook, helping to convert the remaining connective tissue into collagen. When removed from the cooker let it cool for a few minutes then wrap it in foil, then wrap the foiled butt in a towel, and let it rest in an insulated cooler. A rest of 2 to 4 hours will insure the connective tissue is converted into tender, juicy strands of meat. Always plan on the rest when calculating cooking times.
The only exception to use temperature as a guide to reference when pork is done is; If you are looking for sliced pork, you'll want the pork to be a bit more firm for slicing. I would remove the pork from the cooker at about 185 degrees, this is the only case I would use temperature only to dictate when when the pork is ready for slicing.
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