HOW long to cook a 20 lb prime rib roast?

It's impossible to give you an exact time without knowing more about your roast and your oven! Here's why and how to figure it out:

Factors Affecting Cooking Time:

* Roast Size & Shape: A 20 lb roast will take longer than a smaller one.

* Desired Doneness: Rare, medium-rare, or well-done? Each requires a different internal temperature and cooking time.

* Oven Temperature: Lower temperatures (250-325°F) produce a more evenly cooked roast, but take longer. Higher temperatures (400°F and up) are faster but can lead to overcooked edges.

* Bone-In vs. Boneless: Bone-in roasts take slightly longer as the bone retains heat.

* Type of Oven: Ovens vary in their ability to maintain temperature.

Here's how to calculate a general cooking time:

1. Target Internal Temperature:

* Rare: 125-130°F

* Medium-Rare: 130-135°F

* Medium: 135-140°F

* Medium-Well: 140-145°F

* Well-Done: 145°F and above

2. Cooking Time Estimate:

* Slow and Low: At 250°F, plan for about 15-20 minutes per pound (300-400 minutes for your 20 lb roast).

* Medium Heat: At 325°F, plan for about 12-15 minutes per pound (240-300 minutes for your 20 lb roast).

* Higher Heat: At 400°F, plan for about 10-12 minutes per pound (200-240 minutes for your 20 lb roast).

Important Tips:

* Use a Meat Thermometer: The most accurate way to check doneness is with a meat thermometer. Insert it into the thickest part of the roast, avoiding bone.

* Rest Time: Let your roast rest for at least 15 minutes after cooking to allow the juices to redistribute. This makes for a juicier, more flavorful roast.

For the most precise cooking time, consult a recipe specifically for a 20 lb prime rib roast that aligns with your desired doneness and oven temperature.