I'm using a leave in temperature probe for my Thanksgiving turkey. How deep should the probe go into the turkey (I usually put it in the breast) if I am cooking a 18-20 pound bird?
The leave in thermometer can be as deep as you like- just make sure that its not touching the bone for an accurate reading.
A temperature probe is a good idea, but honestly it belongs in the thicker portion of the thigh and not the breast. Breast meat cooks faster than the darker thigh, and if you rely on the breast temperature to decide doneness you could end up with under cooked or raw meat on the leg and thigh. When you insert a probe into the thigh, it normally goes in about 2 inches or so, and kept away from the bones To help prevent a dry overdone breast, start the roasting with the breast side down in the rack, and flip the bird half way through the cook time. It can be scary, but I use a wide spatula and wear an oven mitt to perform the task. If you plan to stuff your bird, it's even more critical to put the probe into the thigh, and to be sure to check the temperature of the stuffing inside before declaring it done. There are plenty of sites on the web, and videos, to show you how and where to place your temperature probe, if you need help with that. If you really, really want to put it in the breast, you need to aim for the thickest part, going in from the front near where the neck and head used to be and parallel to the center breast cartilage. You would still want to double check the thigh though, before declaring the bird finished. If the thigh hasn't reached 165, your bird isn't done roasting yet- even if the breast is. In that case, you'll need a foil breast shield. I fit mine to the raw turkey, before putting it in the oven, so I don't have to wrestle with fitting foil on a hot turkey. It just sits there waiting, until I need it.