how long should an 18 lb prime rib roast cook for if i want it well done?

First let me say that if you are going to roast this expensive cut of meat to well done then you might want to save your money and go with a less expensive cut...Prime rib should be served medium to rare...

Here is how to cook it......

There are two ways you can roast: At a low temperature for a long time, or at a high temperature for a shorter time.

Your roast will shrink less if you cook it low and slow, but you won't get the same flavorful, well-browned exterior that a high roasting temperature gives you.

You can also combine the two methods by starting at a high temperature to sear the outside, then turning down the oven after 30 to 45 minutes to finish. If you're roasting at 325 degrees the meat will take about 17 to 20 minutes per pound. If you start the roast at 450 degrees for the first 30 minutes and then reduce the temperature to 325 degrees.. allow about 13 to 15 minutes per pound.

Which I recommend...

A thermometer is the absolute best way to guarantee the roast turns out exactly the way you want it.... For medium rare, roast to 130-140 degrees... for medium, 145-155 degrees... Remember that the roasts temperature will rise at least 5 degrees after you remove it from the oven. Let the roast stand for 15 or 20 minutes before carving to let the juices return to the center.

The slices taken from the ends of the roast will be the most done, and the middle will be the least done, so you should be able to suit the preferences of everyone .

Enjoy

don't waste your money on a prime rib roast if your going to ruin by cooking it well done.

I'm having ham. Anything with pink showing, I won't eat, so why waste the money?